Experience in a Book
Fuel System Maintenance

Tank, Sump, Pump, Lines

FUEL LINES: The fuel pump in the XJ-S (in the trunk) can put out nearly 200 psi. This is way too much for ordinary fuel hose -- do not use it anywhere in this fuel system. Most auto parts stores now carry "EFI hose." It is much more expensive, but a fuel fire is no fun.

Also, small high-pressure lines usually require special clamps; basic worm screw clamps don't always seal small hoses at these pressures. Some auto parts stores now sell "EFI hose clamps" in various sizes (these type clamps will only fit the size hose intended, you cannot just keep screwing them down smaller liken a worm screw clamp). Sometimes the special clamps are offered in a package with the hose; make sure you have suitable clamps on hand or can buy them separately before buying EFI hose without the clamps. Greg Price says, "The Series III XJ6 has some nice fuel injection hose clamps, and my local Jag tech recommends Mercedes fuel injection hose clamps."

Stefan Schulz says, "Here in the UK, Farnell offer stainless steel hi-torque hose clamps which are The Biz. Highly recommended. Farnell Industrial are on telephone [+44] 113-2636311." Schulz adds that he does not recommend the fuel injection clamps from a Volvo.

The high-pressure hose often is available only in short pieces. It may be necessary to replace a long piece of hose with a length of metal tubing (available at parts shops as hydraulic lines -- cut off the fittings) bent to shape with short pieces of fuel injection hose used at the connections. Get a tubing bender; you don't want crimps at the turns.

Many of the lines (fuel, power steering, etc.) in the Jag consist of metal tubing with threaded connectors and a short length of hose in the middle somewhere, all sold under one part number. The hose typically has a fake braided pattern in the surface, and is no better than other British non-metallic parts. The section of hose can easily be replaced with the fuel injection hose with suitable clamps. It is suggested that before you cut the original hose off, you place measured marks on the tubes on either side of the hose so that when you reassemble, the same overall length can be established. You should also put alignment marks, so the new assembly won't be twisted. Finally, if the hose is within sight of the exhaust system or other hot parts, it might be better to wrap it with some aluminum foil to prevent the radiant heat from cooking the new hose.

The threaded fittings on the ends of some of these lines have brass compression seals. The good news is that these are the very same seals that are commonly used on household plumbing, so they are available at any hardware store. The bad news is that the tubes are so soft that the compression of the seals sometimes has necked the tube, and you can't get the old seal off nondestructively. Often, reinstalling the tubes with the old seals will result in a leaktight connection. If this doesn't work, buy new tubing and use new seals and the old threaded nuts. You may have trouble finding new nuts of the same thread.

The connections on the fuel rail and injectors themselves on the XJ-S do not use clamps; the tightness of the hose on the fitting is relied upon to prevent disconnection or leaks. While this appears to work well, it makes some of us nervous, especially if we have had one of these connections apart for some reason. If you would like to secure the connection, the best way is to use some steel wire -- see below.

ENGINE FIRES: The early XJ-S H.E. had a reputation for engine fires. There has been a redesign of the fuel rail on the engine to solve this problem; the newer design is indicated by rectangular tubing rather than round. All XJ-S H.E.'s were recalled and the new system fitted -- if you still have the old, see your nearest Jag dealer. The non-H.E., on the other hand, still uses a fuel rail with round tubing.

Leaking fuel in an engine compartment is remarkably difficult to ignite. Usually there have been obvious odors and visible leakage for some time. Please do not ignore fuel odors; the XJ-S shouldn't have any.

MORE ENGINE FIRES: The later XJ-S also has a reputation for engine fires, also from the fuel lines! Peyton Gill reports on "an XJ-S that had a little pyrotechnics under bonnet. I asked the guy about it and he said that the fire was put out within 30 sec (owner had a fire extinguisher) and the estimate to repair was $2000.00. There was not that much damage. The cause of the fire was the ignition coil wire was about 1/4 inch from one of the fuel injection lines (between rail and injector). The ignition wire had been arcing to the line and eventually worked its way through. I guess the physical damage and ozone created by the arc eventually broke down the line."

Julian Mullaney adds, "There was a recall for cracked injector hoses and injector bodies. Ozone from the distributor leads causes the perished plastic. The recall replaces the lead with a shorter one, and replaces the injector. They looked up my car (vin no.) in their database and the fix had already been done a long time ago, however the problem persisted.

"The problem was ozone deteriorating the injector hose on the right bank second cyl. from the firewall. It produces a cracked surface of the rubber hose. You should look carefully for this, it's not easy to spot.

"The dealer said that they were instructed to look for visual damage to the hose and replace injector if needed. "If" is the key word here. However, if it looked good, they could get away with only changing the HT lead to a shorter one (thus not close to the injector) and leave the original injector hose. This leaves the chance that damage could be have occurred to the hose but it's not visible yet, leading to the following chain of events:

1. upon initial recall they only replace the HT lead
2. then the hose continues to deteriorate from initial ozone embrittlement;
3. then you see the damage to the hose a year or two later;
4. pyrophobia sets in;
5. then you call the dealer;
6. then they tell you sorry, the fix has already been done;
7. then you find that the recall was done sloppily;
8. then you get pissed off;
9. a) then you think about fixing the problem yourself
10. b) you call the dealer again and insist they fix it again properly
11. then dealer calls Jaguar to authorize 2nd repair
12. they say OK
13. you get it fixed for free

"Option b) worked fine with me, my local dealer was very good about it."

Ron White adds, "I checked the recall database and the recall only affects 1989-91 XJ-S models; this is a result of: "The high tension lead from the ignition coil can move from the production location closer to the #4A fuel injector hose." <snip> "Vehicle description: coupes and convertibles with Marelli ignition systems.""

White had a fire in his car, and thanks to having a fire extinguisher in the trunk and knowing how to use it, his car survived with almost no damage. "I have seen engine fires in other cars and have seen people make the mistake of flinging their hoods (these were American cars) open, only to have the fire flare up 5 or 6 feet because of the added oxygen. I opened the bonnet just enough to get the nozzle of the extinguisher in, and gave it a good squirt. I then cautiously opened the bonnet up and seeing no flames opened it up all of the way and gave it a real good squirt!" White's extinguisher happened to be a Halon type which works wonderfully and leaves no crud on the engine but is bad for the ozone layer and is in the process of being outlawed. Experts seem to feel that a common powder type fire extinguisher would probably work just as well, the only disadvantage being that you'd have to blow all the powder out of the engine compartment afterward.

One more note: White's car is an '86, meaning it's late enough to have had all the updates to correct the early fuel rail problems and too early to be covered by the recall for the later cars with the Marelli ignition. "It appears that the cause was a cracked body on an injector, and it was squirting fuel directly on the distributor!" That fire extinguisher is sounding like a better idea all the time, isn't it?

CATALYTIC CONVERTOR FIRES (MARELLI IGNITION): Might as well call it an engine fire; the level of damage is comparable. Discussed at length in the section on the Exhaust System.

STILL MORE ENGINE FIRES: Just when you think you have the situation under control, the government throws another monkey wrench in -- this time in the form of oxygenated fuels, now required in California and many metropolitan areas. Stephen Wood says, "We starting in Spring 1996 having a substance called MTBE -- methyl tutol-buytol,ethonanal, something like that -- blended with our gas to help reduce emissions. Hopefully they will be taking it out soon, as there has been a major hubbub about it here. You see, it also melts things, like fuel lines, carburetor gaskets, (especially the old rubber/cork type), fuel tanks, braising material solder, etc.

"Last summer car fires were up significantly all over the state, including my brother's '69 Camaro (it was restored). MTBE melted through the carb gaskets on his vintage Holley and poof.

"At that point it got serious, and I checked my fuel lines, and sure enough, they were going way squishy from the inside out. In other cars we have seen it also has melted injector seals.

"If you ask the insurance companies they have had a slight increase but nothing to worry about. No problem, right? Wrong! Most of the cars affected are cars that the insurance industry won't provide fire, theft and vandalism coverage on anyway. If you ask the CHP and the firemen, they know that last summer was a major problem."

So, you need a new type of fuel hose, right? "The problem with the hose issue is that the rubber manufacturers are not going to gear up for a California-only issue. However, some of the new cars have fuel lines made out of a tygon derivative, a newer plastic that is more resistant to these blended fuels (New LT1- LT4- and LS1 GM motors). I don't think there is a crossover app. as of yet, tygon is a bitch to work with and has the characteristics of polypropylene tubing, i.e., firm and not clampable. You have to use special fittings with it.

"There is supposed to be some new silicone-based flexible "rubber like" fuel line coming out soon from Gates or Goodyear but I haven't seen it. So for now, I have been keeping an eye on the situation and checking all pressurized fuel lines every month, and replacing them every 6 months (I have done this three times now). Vent lines are ok from when I replaced them 6 months ago. I have been changing fuel filters every 45-60 days (preventative mania), making sure to cut open the old filter to see if anything weird develops like little bits of rubber hose.

"I will have to take my gas tank out this summer, and have it boiled and welded or just put in a new one. The corrosion around the outlet is growing and I think it is melting through the solder. I may just J&B weld it or something."

FIRE EXTINGUISHERS: After reading the previous few pages, you have probably come down with a healthy dose of paranoia regarding fires in the XJ-S. A fire extinguisher is cheap, and may come in handy.

John Napoli suggests a built-in system like those found on race cars: "It should be a lot easier to extinguish a fire within the closed confines of the engine compartment with the bonnet closed, and you could certainly react a lot quicker than, say, opening the bonnet, saying "Oh, sh$t", running for the boot, trying to find the fire extinguisher that is underneath all your luggage, meanwhile the bonnet is open and the flames are getting higher..." Of course, keeping the extinguisher on the floor in front of the front seat may help.

Emile A. DesRoches says, "If anybody is really interested in a real "racing car" fire control system (sanctioning bodies require a system plumbed in to spray at the engine, fuel cell and driver's lap area), they can be obtained from such organizations as Racer's Wholesale in Atlanta. From experience as an SCCA tech inspector, I can say that they may make a mess, but they work and clean up is inevitably less expensive than replacing a fried V12 motor."

FUEL RAIL HOSE REPLACEMENT: This job is a cinch -- and it's highly recommended for anyone who notices aging or leaking hoses. Take the entire set of injectors off the car, which entails depressurizing the system, removing 24 nuts and disconnecting a couple of fittings. Buy some 1/4" "fuel injection" hose at any auto parts store -- if it's reasonably priced it's the wrong hose, EFI hose is quite expensive. The original hose may look like it has a cloth surface and the aftermarket looks like rubber, but don't worry about that -- the aftermarket is probably better. And you might wanna get some steel wire, about 20 gauge.

One by one, note the position of an injector (the direction the connector faces) and the length of the piece of hose. Cut the old hose loose (don't lose the dished washers), and reassemble by simply pushing the fittings into a new piece of hose cut to the same length.

Now, if you're like me, you don't trust those push-on connections. So, add considerably to your workload by tying each hose connection with the wire. Wrap two or three times around the hose, pull tight, twist, cut off, and fold the twisted part over so it doesn't stab you whenever you're fiddling around in the area. If you're concerned about appearance here, stainless steel wire will look better.

You can buy stainless steel leader wire in any store that sells fishing tackle, but it probably won't work well for this task; the alloy used for leaders is very hard and difficult to wrap. In a completely overblown sidetrack, some advice on finding suitable stainless steel wire: Gregory Price says, "I got a spool of SS wire in the Help section at Pep Boys."

Gordon Clefton suggests, "We use stainless steel safety wire in four sizes in aircraft applications: .020"; .025"; .032"; and .041". The wire comes in one pound spools. Two sources:

Sporty's Pilot Shop ($13.95 each) . . 800/543-8633
Eastwood ($10.99 each) . . . . . . . . 800/345-1178" 

Lee Walden says, "If you're really looking for lockwire, check out Harbor Freight Tools. If they sell the lockwire pliers, they'll have the wire too."

Bill Frenchu suggests:

McMaster-Carr Supply Company
PO Box 440
New Brunswick, NJ 08903-0440

"Stainless Steel "Machine Grade Wire", "Lashing Wire", "Lock Wire", "Tie Wire", "Spring Wire" and "Music Wire". Most available in 1 or 5 lb. spools, in various diameters from 0.009" to 0.125"." Note that the "spring wire" and "music wire" will be very hard, just like the fishing leader wire.

"Also Inconel Lock Wire in Silver and Black." Another note: Inconel is what was used for lock wire at P&WA on jet aircraft engines; it's really excellent and will not rust, even though it's generally not as pretty as stainless steel.

Frenchu continues:

Small Parts Inc.
PO Box 4650
Miami Lakes, FL 33014-0650

"Precision ground Type 304V Stainless Wire, in 30 or 60 inch lengths, shipped "straight," not coiled. Diameters from 0.005" to .104"." Since it's shipped uncoiled, I'm betting this is a hard alloy as well.

Michael Stanford says, "Monel is the alloy of choice for siezing wire in most situations, it has the proper combination of corrosion resistance, malleability and strength. Stainless is generally too hard to be twisted without breaking. Most stuff that is advertised as true stainless is an alloy anyway, usually monel.

"An easy source for a small quantity is West Marine, a catalog boat stuff company. 800-538-0775, a 30' roll of 20 Ga (0.037"), order #127854. They also have stores in most coastal areas of the USA. Sailboaters use siezing wire for safety rigging parts.

"Standard safety/siezing wires and the special tools to properly twist/tension it are also available from Jensen Tools, 800-426-1194. Jensen is expensive and caters to the electronics industry. http://www.jensentools.com.

"The cheapest source is Northern Hydraulics, 800-533-5545, http://www.northern-online.com. Pliers are P/N 15646-C121 and wire is P/N 156461-C121, 365' x 0.032" dia. roll of "stainless". If you don't already have the Northern catalog, get one -- it is a valuable asset."

There is, in fact, a special tool made just for making hose clamps from wire. This is not the same thing as lockwire pliers; lockwire pliers merely twist two wires together neatly. This hose clamp tool is designed to help pull the wire tight around a hose before it is twisted. It's sold under the names ClampTite or Clamp-It, and the claims include that it can use wire to make hose clamps up to ten times stronger than screw-type clamps. The Clamp-It is sold in Australia by

Super Drill Sales
P.O. Box 393
Oakey Q 4401
+61 076 913 162 Fax: +61 076 913 076
Mobile: 018 878 782

FUEL SUPPLY CHECKING: It is often useful to know if the fuel supply to the injectors is working properly. To do this, Robert Dingli suggests installing a fuel pressure gauge: "I bought a VDO fuel pressure gauge for about Aus$40 and connected it to the fuel rail where the cold start injector was once supplied. I believe any pressure gauge designed for hydrocarbons would be suitable and other brands sell for much less. My gauge is mounted in the engine bay as I am paranoid about high pressure fuel entering the cabin.

"There are a couple of things to note about connecting the gauge :

• use high pressure fuel line and fittings.
• don't mount the gauge on the engine as vibration will kill it.
• use a restrictor in the line as the pressure fluctuations will also kill the gauge."

FUEL ODORS: Jaguars seem to be prone to fuel odors; the XJ-S was even recalled to provide a more positive vapor recovery system. Please note that while Jaguars often smell like fuel, they're not supposed to; it is an indication of a problem, and should be addressed.

One excellent suggestion is to trot the car right down to your local Jaguar dealer, or anyone else with the equipment to test automotive emissions. The testing equipment includes a probe that is inserted in the tailpipe to detect unburned hydrocarbons (fuel). This probe is real handy for finding fuel leaks anywhere in the car.

There is a relay in the trunk through which the EFI controls the fuel pump. If you remove the relay and jump connectors 86 and 87, the fuel pump will run whenever the ignition is on. This is useful for searching for fuel leaks without having to leave the engine running.

There are a couple typical places to check for sources of odors. The fuel filter is the size of a Coke can and is located behind the spare tire in the trunk. When this filter is replaced, it is all too easy to spill its contents within the trunk. The nature of the foam padding under the carpet is such that once this happens, your trunk will smell of fuel for all eternity. The only suggested fix is to replace the carpeting and padding. It is recommended that before the filter is replaced, and before any repairs to the fuel system in the trunk are carried out, the carpet be removed.

Possible locations for leaks include the fuel tank itself, located over the rear axle. It is accessible by removing the spare tire and some other stuff, then pulling the carpet out. The tank sits on a thin pad. Meanwhile, on the underside of the car there are numerous lines that are held to the car with little clips and rivets. One of these rivets is in the panel the tank sits on, and sometimes the weight of the tank compresses the pad enough that the metal tank contacts the tip of the rivet. After some vibration, the contact can wear a hole in the bottom of the tank. Once the tank is drained and removed, it is a simple matter to patch the hole (there are types of epoxy sold that will work well) and find an alternate way of supporting the item under the car.

Officially, the recall supposedly was to prevent excessive pressure/vacuum cycles on the tank, resulting in stress cracks. Obviously, this is something else to check on your tank.

Chad Bolles reports that the seal around the rear windshield starts leaking, and the water soaks the sponge under the tank and causes the tank to rust.

The tank is connected to the filler cap with a short piece of hose and some clamps, accessible from within the trunk by removing some carpet. Another place to check for leaks.

As described above, there are several fuel lines that include a piece of hose in the middle of a metal tubing assembly. Despite the pressure, these hoses often weep fuel rather than burst. One of these pieces of hose is in the high-pressure line directly over the right rear wheel arch, and is difficult to see because of some heat shielding. Check all of these lines with the pump running, and replace any hose you even suspect of being the cause of odors.

Derek Hibbs says: "The answer for my fuel smell was simple, the fuel cap overflow pipe was disconnected and any spillage during refueling was draining directly into the boot/trunk instead of onto the ground. Reconnected the overflow pipe and no smells (I also take more care when refueling)."

Also check the components of the vapor recovery system -- see below.

FUEL TANK LEAK REPAIRS: If you have tank leaks due to perforations, one good solution is to coat the inside of the tank -- and it forever ends the concerns about rust scale from the tank fouling the fuel pump as well. John Whitehead says "I have used gas tank sealer from Bill Hirsch Automotive, with great success. I put it in the fuel tank of my '67 XKE which had a number of pin hole size leaks. Previous attempts to coat the outside of the tank were not as successful. The tank sealer is gasoline and alcohol resistant. A quart can is sufficient as only a thin film is coated to the inside of the tank. I am not sure of the product's chemistry, but it dries to a white Teflon-like film." Obviously, major cracks or holes will require more extensive repairs.

FUEL COOLER: Many people see that the air conditioning circuit in the Jag includes a fuel cooler, and assume that this is a high-performance trick. Dragsters often include an ice bucket in the engine compartment to cool the fuel on its way to the engine to get more horsepower.

It's a great idea, but unfortunately not the case. The fuel cooler in the Jag is in the return line going back to the tank. The pump moves much more fuel than is normally needed and most of it recirculates. The fuel being heated while passing through the engine compartment as well as the pumping energy itself would eventually heat up the fuel in the tank significantly, possibly causing vapor lock problems and problems passing EPA emission requirements -- heated fuel gives off more vapor. The cooler is to counteract the heating effect. This may help explain why the ventilation system has the A/C running during most conditions.

Why Jaguar doesn't put the cooler in the supply line and reap both benefits is anybody's guess. Perhaps it's more difficult to make a cooler to operate at the higher fuel pressure on the supply side.

FUEL COOLER - CONVERTIBLE: According to Michael Neal: "This vapor lock problem was such a problem that the convertibles were modified to keep the A/C compressor running all the time. The aerodynamics on the convertibles caused the engine compartment to run even hotter than the coupes. With the A/C compressor running the fuel cooler kept the fuel temp to a decent level."

HOT STARTING: The fuel cooler works great when the engine is running, but is worthless after the engine is shut off. The heat rising from the engine heats the fuel in the rail, which is not moving. If the engine is started about a half hour after shutoff, it may have difficulty starting.

Jaguar has provided two different fixes for this problem. Both involve a temperature sensor in the boss on the left side of the fuel rail; the boss has no opening into the fuel, but the sensor has a copper bottom that presses against the rail to sense the temperature. The boss itself seems to exist on all XJ-S's, since a recall replaced the rail after the hot fuel problems were found.

One type sensor has vacuum connections, and is connected between the intake manifold and the left side fuel pressure regulator. The other type sensor is electrical, and is connected in line with the inlet air temperature sensor for the EFI system.

FUEL COOLER - 1992-ON: Richard Mansell quotes from a Jaguar publication that was sent to him: "It is titled "Technical Guide - The New XJ-S 1992 Model Year Preliminary Information". In it there is a paragraph about the fuel cooler deletion, it says:

With the introduction of the in-tank fuel pump, the fuel cooler is deleted. This affected the characteristics of the system so that a muffler is added in the line to reduce noise and vibration.

"I wonder why adding an in-tank fuel pump should allow the deletion of the fuel cooler. It also says in another section:

As a result of the deletion of the fuel cooler, it is necessary to introduce a redesigned hot start system. The thermal vacuum valve fitted to pre-92 MY vehicles is replaced by the following components:

1. Fuel rail temperature switch. The electrically operated switch enables the fuel rail pressure to be increased when the fuel temperature exceeds 70 degrees Centigrade at hot starting.

2. 45 second timer module. The timer limits the time for which the increased fuel pressure is applied.

3. Solenoid vacuum valve. This controls the vacuum signal driven by the fuel temperature switch and the 45 second timer.

4. Vacuum delay valve. This controls the way the extra pressure is applied at hot starting to give a decayed reduction in fuel pressure over 45 seconds, after which the pressure is switched to normal.

 

 

FUEL PICKUP: The following tip was sent by Leonard Berk of Howard Beach, NY: Apparently his XJ-S would run fine when first started, but after a half hour it would start to lose power, eventually coming to a stop. After shut off, it would start and run fine for another half hour. After much head scratching, it turned out the problem was dirt in the small sump tank in the trunk. Apparently, as the engine ran, the dirt would gradually collect on the screen on the pickup and plug it. When the engine was shut off, the dirt would fall back to the bottom of the tank.

There is another potential problem with this pickup screen. It is a molded plastic item, and is installed by simply sliding it onto the metal pickup tube until it bottoms on a shoulder on the inside of the screen. The shoulder is not very big, however, and the screen has been known to get sucked on and over the shoulder until the bottom of the screen meets the end of the pickup tube. This reduces the effective area of the screen by about 80%, and the screen will clog much more easily. To prevent this, put a hose clamp or other obstruction on the tube for the base of the screen to rest against, so that it does not rely on the internal shoulder.

However, there is some experience to indicate that this problem is often accompanied by a failed fuel pump. Perhaps the plugged pickup causes the pump failure. Be aware that when you find the pickup problem you may also have to replace the pump before the car runs right again. Apparently, if you can hear the pump whining when driving, you can count on it. Perhaps the cost of this pump is enough to justify checking the pickup before you have problems.

John Goodman owns a 1989 XJR-S 6.0 litre: "I have just cleaned out my sump tank, no signs of a filter!" Who knows, maybe Jaguar decided it was more trouble than it was worth.

Goodman also came up with a neat procedure for emptying the sump so you can work on it. "What I did was to clamp the fuel hose from the tank to the sump with some vice grips, start and run the engine till it stalls which soon empties the sump." Since the sump is vented, the pump can draw out of the sump without drawing a vacuum. The pump draws the fuel out of the sump and returns it to the tank; it would empty the tank by itself if you can run the pump without starting the engine.

FUEL PUMP CONTROL: On the Digital P system anyway (I dunno about the D Jetronic), the fuel pump is controlled by the EFI ECU via a relay in the trunk. The ECU contains a circuit that determines whether or not the engine is actually running and shuts off the pump if it has been motionless for more than a coupla seconds. This is for safety reasons.

Unfortunately, this circuit is reportedly unreliable in the 6CU, and sometimes will fail to keep the pump running more than a coupla seconds regardless of whether the engine is running or not. Typically, the starter is engaged, the engine fires, the starter is released and the engine quickly dies -- misleading the mechanic to believe that the problem is related to coming off the starter circuit.

If you'd like to test this circuit to determine if this is your problem, simply remove the fuel pump relay in the trunk (the one without a red mark on it) and put a jumper between terminals 86 and 87. This will allow the pump to run whenever the ignition is on. If the car now runs perfectly, the fuel pump circuit in the ECU (or the relay itself) was the problem. AJ6 Engineering, as well as other places that repair ECU's, should be able to fix this problem for far less than the cost of a new ECU. If you're willing to risk the odds that you will be in an accident where you are knocked unconscious, a fuel line is severed, and something ignites the leaking fuel, you can leave this jumper in place permanently.

FUEL PUMP NOISE: Noisy fuel pumps are a very common complaint. Goodman suggests: "it may not be the pump causing the noise, try the hose clamps on the fuel outlet pipes from the pump vibrating against the boot floor or battery stand. Fuel filter may be blocked causing strain on the pump or the filter may be vibrating against the tank or spare wheel, steel fuel lines vibrating under the floor etc."

FUEL PUMP VARIATIONS: Goodman reports: "The latest XJ-S's had pumps inside the fuel tank, so Jaguar may have done this for noise related problems. I suspect that these pumps are lower output because the '93 model XJR-S had twin in-tank pumps, and must be ordered in a matched pair."

Hess & Eisenhardt Convertible

FUEL TANKS: This section is of no use to coupe or later convertible owners, but it is reportedly difficult for H&E owners to find information on how this system works so a description is included here. According to Mike Cogswell, "In order to make room for the folding top and its mechanism H&E had to take the standard tank and cut part of it off. It would appear they literally cut the tank and welded in a sloped section. To regain fuel capacity, they added a second tank under the parcel area, basically where the rear seat would have been in a coupe. The upper tank is about 14 US gal. and the lower is about 11.

"As you know, the standard tank has a sump from which the high pressure fuel injection pump draws its fuel. Since the second tank is lower than the first H&E added two concentric hoses. The larger outer hose allows fuel to gravity drain into the lower tank from the upper (which is where the filler neck is located.) Consequently, the lower tank is always full until the upper tank goes dry. Meanwhile, a small submerged pump constantly pumps fuel from the bottom tank to the top tank via a small tube that is located in the center of the large drain hose. The fuel is dumped into the upper tank's sump, where it is available to the main fuel pump. The submerged pump can pump fuel faster than the engine consumes it, but any in excess of the sump capacity will drain right back into the lower tank. Both pumps only run when the ignition is on and the standard pump circuit is energized, so all the regular safety interlocks still work.

"Each tank has its own fuel level sending unit. The upper unit is apparently the standard XJ-S tank unit. The lower one is similar, except the mounting plate is horizontal instead of vertical. The two gauges are wired in series. There is a small circuit board in the H&E harness that theoretically turns on the low fuel level light.

"My gauge is wildly inaccurate. Because they are in series I'm guessing that my top one basically hits bottom well before the bottom one starts to drop. As a result, my gauge is very non-linear."

Tim Blystone points out that since parking the car nose-down on an incline will cause the fuel to drain toward the forward tank and away from the sump, the auxiliary pump might not keep up when the tank is less than half full. "All of the early tank designs will stall on a sufficient incline."

"H&E went through a couple of different configurations. The main difference is the dams added in the interior of Jags original tank."

FUEL HEATING PROBLEMS: The stock Jaguar fuel pump moves far more fuel than the engine normally needs with the excess returned to the tank. Since this heats the fuel somewhat, a fuel cooler is included in the return line, using the A/C freon circuit to provide cooling. On the H&E, however, the problem is exacerbated by the fact there are two pumps running full time, coupled with the fact the car is a convertible so the top may be down and the A/C off on warm days! Tim Blystone: "Normally this presents very little problems until the A/C goes on the fritz, or you have one of H&E's earlier designs. If it is summer, the top is down... the AC system is off. No cool fuel. Vapor lock from hell."

FUEL SYSTEM MODS: Tim Blystone: "My modification puts the plastic hose from the H&E fuel cell directly into the supply for the sump tank. A new and longer piece of hose is required. Fuel is pumped by the H&E pump directly into the Jag sump tank and bypasses the need for the tank to be gravity filled. There is a return to Jags original main tank from the sump tank so there is no excess pressure in the sump. The result is a fuel system that doesn't have the H&E problem with steep inclines or die dead in the middle of a hot southern day."

GAS CAPS: The single gas filler on the H&E is the same as the two on an XJ6.

Vapor Recovery System

VAPOR RECOVERY SYSTEM: When the car is running and drawing fuel out of the tank, there must be a vent system to allow air into the tank to prevent a vacuum from being created. It is no longer acceptable to merely have a small hole in the gas cap; such methods allow fuel vapor to escape into the atmosphere all the time, whether the car is running or not, and would contribute to air pollution. Now, unless you live in California or somewhere else where they have intelligently-designed gasoline pumps, you pump 20 gallons of fuel vapor out into the air every time you pump 20 gallons of liquid gasoline into your car, and proper fuel tank venting begins to look like an inconsequential issue. But we will endeavor not to get into a discussion of the real intentions of our legislative bodies.

Nowadays, the vent system from a fuel tank is connected to a carbon canister. Air can flow freely through the canister into the fuel tank, but when vapors from the fuel tank try to escape through the canister they are absorbed by the activated charcoal.

Of course, the charcoal can only absorb so much fuel. Therefore, whenever the engine is running, there is a system by which the engine draws fresh air through the canister. This draws the vapors back out of the charcoal and burns them in the engine.

When the car is not run for extended periods of time, the amount of vapor generated in the tank could be considerable. Gradual changes in ambient temperature and barometric pressure would cause the vent system to "breathe", running a large amount of vapors through the canister. To absorb all this vapor, the canister would have to be prohibitively large.

To prevent this, there is a valve in the vent line between the fuel tank and the canister. This valve will allow air to flow in either direction, but only after a certain pressure or vacuum has been reached. If the contents of the tank expand and try to escape out the vent, it will prevent any flow until the pressure reaches a set value, and then it will allow it to pass to prevent damage to the tank or hoses. Similarly, if the contents of the tank contract and try to draw air in through the vent, the valve will prevent any flow until the vacuum reaches a set value, and then it will allow it to pass to prevent the tank from collapsing. As a result, the vast majority of the smaller expansions and contractions do not open the valve at all, and the amount of vapor the canister is expected to absorb is greatly reduced.

Of course, this means that at any given time the fuel tank and hoses may be slightly pressurized, even when the car is not running. Even the tiniest leak anywhere in the system may become quite significant.

The carbon canister vent is an excellent system, does not hurt the performance one iota (as opposed to some other emission control systems) and is normally maintenance-free. Activated charcoal can absorb and release fuel vapor forever, it doesn't wear out or get "full". However, there are filter elements within the canister (after all, it is an air intake) that may eventually get clogged, and the carbon itself may eventually get contaminated with fuel additives or other non-petroleum substances, so it is recommended the canister be replaced once in a great while.

If you're really a skinflint, the carbon canister can be opened and the filters replaced. There are two, one at the top of the charcoal and one at the bottom -- you must dump all the charcoal on a newspaper or something. Both filters can be neatly replaced with coffee filters. The canister can be held shut with aluminum tape when reassembled.

The carbon canister itself has an opening on the top to atmosphere, and three fittings on the bottom. The fitting labeled T is connected to the fuel tank, via the appropriate valve and the vapor separator. The fitting labeled P is the purge line to the engine. The fitting labeled C is capped off; it originally was the connection for venting the float bowls of the carburetors, but they are history. Note: if you fit carbs, do not simply open this fitting and try to use it; a screen has been omitted inside as well, and you will draw carbon granules into the floats.

One of the possible causes of the common fuel odors is the location of the canister in the XJ-S. On most cars, it is located in the engine compartment where any escaping fumes will simply be blown away by the flow of air through the radiator. But in the location in the bodywork forward of the left front wheel, there is no such flow. The vapors may gather in the bodywork and eventually work their way to the passenger compartment. Of course, there aren't supposed to be any fumes escaping, so this is a secondary problem. However, it might be a good idea to connect a length of hose to the atmospheric vent on the canister and route it out the bottom of the car.

Another possible failure mode is that the engine is not properly purging the canister. If the engine is not drawing air through the canister when running, the canister will quickly become saturated with fuel and will cease to absorb, and any further fumes coming down the vent line will escape to atmosphere.

VAPOR RECOVERY SYSTEM -- AFTER RECALL: The original XJ-S vapor recovery system pretty well followed the description above. However, there was a tendency for the tank to develop stress cracks from excessive pressure fluctuations as well as indications it did not vent as well as intended (including numerous complaints about fuel odors), so there was a recall to address the system. In general, the recall involved the installation of Rochester valves in place of the pressure-operated tank vent valve. Basically, a Rochester valve works the same way as the earlier pressure-operated valve when the engine is off, but when the engine is running a vacuum signal opens the Rochester valve wide open to freely vent the tank. The recall also installed a pair of vacuum-operated purge valves to provide a positive purge when the engine is running. The left side throttle butterfly housing was replaced with one that had suitable taps for controlling the Rochester valve and purge valves.

David Johnson: "The Rochester valve (Part CBC 7714) is a cylindrical disk (approx 2 inch diameter) with an inlet from the fuel tank vent pipe and outlet for the vent to connect to the carbon canister. A third outlet at the top is to connect to the manifold vacuum. This top vacuum pipe opens the Rochester valve when the engine is running. Hence you should not have pressure in the fuel tank when the engine is running (If you do, check the Rochester valve). The location of the Rochester valve is next to the carbon canister under the front left wheel arch. The valve stops the fuel tank from venting below 2 psi, (i.e. the valve only opens above 2 psi on the fuel tank side), and the valve opens due to a small vacuum on the tank side. That is why you get a whoosh when the car is standing on a hot day. A simple check is to open the tank cap after standing for some time on a hot day. A huge whoosh and an oil canning sound means the valve is not working -- the vent is connected wrong, or the vent is blocked. If you have no whoosh then the vent pipe or fuel tank is leaking, and the car will either have a fuel leak or a fuel vapor smell. It is important to disconnect the Rochester valve and check it opens at 2 psi and under vacuum. Also note the Rochester valve must be connected in the correct direction. It all sounds complicated, but the system is simple."

For those who have disconnected the vacuum lines from the butterfly housing and want to reconnect them properly, I can give this guidance based on the dealer instructions for the recall that installed the system in the first place: Among the two vacuum hoses that go from the butterfly housing to the area in front of the left wheel well, one is supposed to have a black and white delay valve in it, hanging in the vicinity of the coolant header tank. A hose from the black side of this delay valve should be connected to the front port on top of the left butterfly housing. The hose with nothing in it should be connected to the rear port on top of the butterfly housing. Of course, there were several variations on this system as applied to different cars, but I think that description should cover most of them.

VAPOR SEPARATOR: In the XJ-S, there are several vent lines from the fuel tank. They all are routed to a small vapor separator high in the bodywork to the right and above the fuel tank. This small metal contraption is intended to allow most fuel vapor to condense and drain back into the fuel tank. The vent line to the canister is routed from a point high in this separator, so fuel vapors must be very determined indeed to make it past this point.

Note that the vapor separator has been blamed for many problems. Since it is steel, it is prone to rusting. If a hole rusts through it, fumes will be vented into the bodywork. Also, rust particles may fall inside it and plug the tiny vent passages and hoses.

Hess & Eisenhardt Convertible

VAPOR RECOVERY SYSTEM -- INCORRECT PLUMBING: David Johnson owns two H&E's, and reports: "I found that on both of my cars the fuel vent systems were plumbed incorrectly (not done by my local dealer). The carbon canister under the front left wheel arch is connected to a vent pipe from the fuel tank, and a vent pipe to the PCV valve next to the LHS air intake. The two vent pipes were wrongly connected, i.e. the fuel tank vent was connected to the valves for PVC pipe (two valves operated by vacuum from the LHS manifold), and the PCV vent pipe was connected to the Rochester valve that should be connected to the fuel tank vent.

"So what's the big deal? Well, the valves that would normally operate the PCV valve only open under vacuum when the engine is running. When parked and sat in the sun the tank cannot vent! I tested these valves with 10 psi and still the valves would not open. The tank is now a sealed container with fuel vapor inside! There are only two things that can happen:

(a) The tank will build up a severe pressure and will rupture in time due to fatigue at the weakest location. A pressurized gas vapor canister in my car/garage does not give me a good feeling!

(b) If you are lucky, one of the vent pipe/fuel connections will leak to relieve the pressure and cause a fuel leak and/or a fuel vapor smell. I am still not keen on this option with the car in my garage!

"If the tank is connected correctly to the Rochester valve, the valve will open at approx. 2 psi to relieve the pressure in the tank, and also opens under vacuum. This stops the tank venting under all conditions and hence does not overwhelm the carbon canister.

"Of course my vent works perfectly now, no gas smells and no severe pressurization of the tank, just a small woosh when I open the tank cap. I wanted to pass on this info to others, since I consider this a dangerous fault, in this case not a design fault but an incorrect installation by the Jag dealers on two cars! Very ironic since the recall was to solve this problem."

"This recall was Hess specific (recall (C002) XJ-S purge kit (Feb 1990). If you check the recalls on XJ-S 86-91 you will find there were similar problems with the regular XJ-S but a different fix. The mod was estimated to be 4.35 hrs for later Hess cars to install Kit JLM2046 and conduct a fuel system integrity test.

"The diagram (figure 6, page 8 of 23) showing the valves and carbon canister connections is not very clear because the fuel vent pipe connections are only partly shown, but the PCV pipe vent connections are clearly shown. I deduced these pipes were incorrectly attached by testing all the valves to determine how the vapor system functioned. I called the Jag dealer the next day to get a copy of the fuel vent recall, and hence confirm the connection was incorrect.

"I do not think the two cars were fixed by the same dealer for the recall. One car is from New York, and the other is from California. That is why I suspect other cars could also be connected wrongly!"

Throttle Linkage, Idle Speed Adjustment

IDLE SPEED ADJUSTMENT: On each butterfly housing, there is an adjustment screw that a lever contacts when the throttle is at idle. These are not to be used for setting idle speed. If they have been disturbed, the linkage must be readjusted.

Underneath the rear end of the left intake manifold there is an aluminum housing with two hose connections; one that goes up to the back end of the manifold and one that goes forward to the air filter housing. Just below the connection leading to the air filter housing is a bolt. This bolt, believe it or not, is the idle speed adjustment. The bolt itself obstructs an air passage, so the farther the bolt is unscrewed, the more the passage is opened, and the faster the engine idles. It's not real convenient to get to, but a ratchet and a long extension with a swivel at the end will do it. The bolt requires a 13 mm socket to fit.

AUXILIARY AIR VALVE: If you have tried to adjust your idle using the above method and turned the screw all the way in and the idle is still too high, chances are good that your auxiliary air valve (also called an "extra air valve" in Jaguar repair manuals) is stuck open. The auxiliary air valve is in the same housing that the idle adjustment screw is on, and is supposed to open when the engine is cold to keep the idle up. To check to see if it is the problem, remove the left side air filter cover and element, start the car and let it warm up, and check how much air is entering the hole where this valve is connected.

Per Jan Wikström: "It's a particularly dumb design, unfortunately, being a slide valve - one tiny speck of grit or a modest accumulation of soot and it jams, and if your engine boils, the wax bulb that operates it can expire. You can overhaul these valves, though. When you look down the neck from the top, you'll see a part with about six holes (there are variations) in it; that's the actual valve. If you make up a tool with six flat-ended pegs to pass through these holes (about 2in long, from memory) you can press out the brass bulb unit in the bottom - carefully; the pegs need to be as large as you can fit through. You can now clean out the bore and the valve slider and press the bulb back in."

Mike Morrin: "On my car, the auxiliary air valve was stuck in the closed position, which caused the car to stall when cold. My method of disassambly of the auxiliary air valve was different: I mounted the valve in a lathe with the thermo bulb away from the chuck. I then carefully skimmed metal from the bottom of the aluminium housing until the thermo bulb dropped out. This made the housing about 5mm shorter than standard. I then fabricated a plate from 5mm aluminium which had the same mounting holes as the valve body, but a hole in the middle which was a snug fit for the thermo bulb (and too small for the flange in the bulb to slip through). After freeing up the sticky valve, it was reassembled with its new spacer plate and a good dollop of silicone sealant and has given no problems since."

OVERRUN VALVES: If the throttle is closed at an elevated RPM, the manifold vacuum can exceed that normally found at idle. Under such high vacuum conditions the fuel/air mixture being introduced into the cylinders, even at the proper ratio, can be so rarified that it cannot be reliably ignited with an ignition spark. If that cylinder full of unburned mixture is then exhausted, it dumps quite a load of raw hydrocarbons into the atmosphere. However, as Roger Bywater points out, an even worse result (from the car owner's standpoint) is what happens when the mixture is later ignited within the exhaust system; it can blow the mufflers open. This igniting within the exhaust is what causes the "backfire" upon deceleration that is characteristic of some cars -- mostly pre-EPA cars.

The little housing at the forward end of each intake manifold contains the overrun valves. They are a spring-loaded poppet valve that should be adjusted to open when the manifold vacuum is higher than a set amount more than idle vacuum. Basically, this limits the manifold vacuum to a level where ignition is reliable. It also tends to make the engine feel as though it has no "compression" on deceleration -- basically, the throttle is being opened a little. In fact, on some other automobiles, the same effect is achieved by physically opening the throttle.

Unfortunately, Bywater reports that the springs in these valves get weak with age, and the valves may start opening at idle. This causes a high idle, and often erratic. If you remove the housing and look at the valve, you can see it would be very easy to adjust -- but what do you adjust it to? Basically, adjust it just tight enough that the valves are closed at idle -- which can be confirmed by putting a finger over the hole in the filter housing with the engine idling. Bywater says, "Setting the over-run valves by checking with finger over the hole is as good as any method. As long as they don't leak at idle but work when you blip the throttle and release it to create an over-run condition they will be OK. You will probably hear them anyway. Actually they only lift a few thou and should be set to open at about 20" mercury."

ACCELERATOR PEDAL -- EARLY MODELS: Mike Morrin says, "The Jaguar pre-HE service manual seems not to have been updated from 1975 to 1981, which is fine for my car, but I have seen a few things which are obviously wrong for most of the pre-HE cars. A minor example of this is the RHD accelerator pedal assembly: The only type shown in the manual was only fitted to the first 200 cars."

THROTTLE LINKAGE BUSHINGS: There is a throttle shaft on each side of the engine, parallel to the heads, that transmits throttle motion to the butterflies. The rear end of this throttle shaft, along with some linkage, is supported by a plate bolted to the rear of the intake manifold. There is a rubber bushing in the plate for the shaft to turn in. This bushing is probably shot -- British nonmetallic parts again. This bushing will dry up, crack to pieces, and fall out, leaving the throttle shaft to wallow around in the opening. In fact, this is another example of a 100% failure mode in the XJ-S; if you haven't already replaced the bushings, they are probably bad right now. The effect on the throttle operation is not good, as it tends to screw up the sync of the two butterflies with each other and with the throttle pot in the bellcrank. There are also reports that this problem can have adverse effects on emissions tests, especially if one bushing is gone and the other is still on the job.

The part number for the original Jaguar rubber bushing is C34388. However, I don't think anyone in their right mind would recommend the original bushing -- it's rubber, for heaven's sake. Rubber throttle linkage bushings are a relic from cars with rigid linkages from the pedal to the carbs; since the engine moved around on its mounts, some means had to be provided to connect the pedal on the car to the butterflies on the engine without the engine's motion affecting the throttle position. The solution was to have one rotating shaft with one end mounted on the car and the other mounted on the engine; the pedal was connected to a bellcrank right next to the mount on the car, and the butterflies were actuated by a bellcrank next to the mount on the engine. The pedal twisted the shaft which opened the butterflies, and engine motion would rock the shaft back and forth without twisting it. Rubber bushings were needed at the ends of such shafts to isolate engine vibrations from the rest of the car, and to allow the small angular motions of the shaft without any binding.

None of this applies to the XJ-S. The motion of the engine relative to the car is dealt with via a throttle cable. The linkages where the bushings are used involve shafts that are mounted at both ends from the same intake manifold, so there is no relative motion. Totally rigid bearings will work fine.

This application really begs for nylon bushings, but bronze bushings would probably work just as well if you can install them so they wouldn't rattle or jingle. The shaft is 5/16", and the hole in the plate is 1/2". With a little looking, it should be possible to find a suitable generic bushing to use here. A bushing with a single lip will work; retention won't be a problem since it is effectively trapped.

Most auto parts stores carry replacement nylon bushings for a Chrysler windshield wiper linkage that can be made to fit, but it requires quite a bit of cutting since the OD is too large and must be cut down. It also has a closed end and an anti-rotation tab that must be cut out.

Replacing this bushing looks difficult; it appears to require removing either the throttle body or the linkage support plate, either of which is a pain. You may choose to remove the linkage support plate, since it will permit you to fiddle with the bushing installation away from the car -- or take it with you when shopping for a bushing.

David Littlefield describes a shortcut: "I was able to replace both my bushings today in my '88 XJ-S without removing either the throttle body or the linkage support plate. I first loosened the pinch bolt on the short rod that is between the bushing and the throttle body. I then removed the spring clip that holds the spacer that fits against the bushing. By sliding both the spacer and the pinch bolt as far as I could towards the front of the car, I was able to gain enough clearance to push the rod towards the rear of the car for the ball end of the rod to come out of the throttle body fitting.

"Once I had the rod out of the car, I was able to move the pinch bolt even further back-- past the knurled portion and right against the shoulder. I then took the new bushing to my bench grinder. I carefully ground down almost all of the lip on the beveled side. I put the bushing on the rod, then fitted the rod back in the car, pushing the rearmost end in first and then putting the ball end in the throttle body fitting. I then pushed the bushing into place, while still on the rod. Removing almost all of the beveled lip on the bushing allows the bushing to be pressed into place while on the rod, since distortion of the inner diameter of the bushing is minimal. Replacing the spring clip behind the spacer and resetting the pinch bolt completes the procedure.

"As stated in the book, a bushing with a single lip will work since the bushing is effectively trapped. There are no real worries about the bushing slipping back on the rod because the spacer and spring washer hold it in place.

"I used the factory bushing for this procedure, but I see no reason why it wouldn't work with others." Littlefield gets two demerits for replacing a British nonmetallic part that failed with another part just like it -- but at least, using his method, it won't be too difficult to replace them again.

Jeff Elmore offers a different shortcut: "I remembered someone saying that it was easy if you did (something) and slid the shaft back through the throttle housing. Well, after some contemplation, I figured he meant removing the screws from the shaft-to-plate and sliding the plate out of the shaft and sliding the shaft forward through the housing. Well, it worked like a charm and the bushings were replaced in about 20 minutes."

If you'd like to try a more expedient fix, John Napoli describes a method he credits to Gerry Duff: "We just cut a couple of pieces of rubber hose. Slipped right onto the shafts, and is the right OD. No tools or disassembly needed. Been working fine for almost a year, and when they wear out 5 minutes to do it again. When the repair was done, the rubber hose sections were left long enough so that they could be turned around if excessive - and quick - wear was realized until a more conventional repair could be effected. Last week I asked the owner how it was holding up. He pulled the hoses, and stated that there was no visible sign of wear at all -- he had never needed to turn 'em around." Note: this author tried using this method on a friend's car, and couldn't get it to work. It apparently requires a particular type of hose we didn't have on hand; we were trying to use fuel hose, which was a little too fat to fit through the hole properly and tended to "walk" off the shaft when the throttle was moved repeatedly. Napoli suggests that the hose used with success may have been vacuum hose.

As Leslie Winfield discovered, a generic bushing with no lip will work if you can figure out how to hold it in place -- and can make installation almost as easy as Duff's fix. "I purchased a 1/2 inch x 5/16 inch bronze bushing 1 inch long, and two 1/2 inch outside snap-rings. I ran a 5/16 bolt through the bushing, pinched it with a nut & chucked it in my drill press (poor man's lathe). I shaved about .005 inch off the OD with a flat file, used a hacksaw with a 24 tpi blade to cut a groove about 3/32 of an inch from each end deep enough for the snap-ring, and then cut the bushing into two halves. With a little fiddling, the snap-ring can be threaded to the inside of the support plate, the bushing can be slid over the shaft and through the hole in the support plate (grooved end first), and the snap-ring positioned into the groove on the bushing. The bushing is now captured on the shaft, and almost no play is observed with this setup. It doesn't look too bad, cost $1.07, and it should last as long as my '79 XJ-S does." Of course, if you happen to have purchased bushings with a flange, you can still use this method by cutting the groove in the opposite end from the flange. While buying these bushings, you might want to buy a spare one in case you ever need to replace the thingy in your Lucas distributor.

After bushing replacement, the linkage should definitely be adjusted as described below.

THROTTLE LINKAGE ADJUSTMENT: If the butterfly stop screws have been disturbed, the linkage bushings have been replaced, or any other tinkering has been done that could mess up the linkage adjustment, it should be readjusted. I'd like to simply dump this description off on the repair manual since any decent repair manual would provide a step-by-step procedure that's easy to follow, but unfortunately the procedure described in the Jaguar XJ-S Repair Operation Manual (Section 19.20.11 followed by 19.20.05) is only barely discernible and the one in the Haynes manual (Chapter 3, Section 47 followed by Section 37) is bloody awful. So, I will endeavor to explain the process here more clearly.

There are four distinct adjustments, which must be done in order because each affects the others.

First, disconnect the crossrods from the throttle pulley by prying them off the ball joints, and remove the air filters. Loosen the locknuts and turn in the butterfly stop screws until they don't interfere with the butterfly motion. Open a butterfly, insert a feeler gauge between the butterfly and the housing, and let the butterfly close on it. What size feeler gauge? Well, therein lies a question. The earliest Jaguar repair procedures specified a 0.004" (0.105 mm) gauge, but after 1978 it was changed to a 0.002" (0.05 mm) gauge. In theory, it shouldn't be too critical; the change may have been made because some of the thicker feeler blades were too stiff to bend to the shape of the throat, and held the butterfly too far open. The 0.002" gauge probably would work fine on all cars. Some have suggested a piece of paper works best. Whatever, with gauge in place, adjust the stop screw until it just touches and tighten the locknut. Repeat for the other butterfly.

Second, loosen the clamp on the lever at the rear end of the butterfly shaft, directly below the crossrod attachment. Allow the spring to hold the butterfly against the stop, and hold the crossrod attachment ball joint in the idle position, where it contacts its own stop. Take up all slop in the butterfly shaft coupling (adjacent to the butterfly stop) in the opening direction, and retighten the clamp. Repeat for other side.

Third, connect the crossrods at the outer end only, and offer up the other end to the pedestal ball joints. The lengths should be such that the sockets can line up without moving anything. If not, loosen the locknuts on the crossrods and adjust accordingly.

Fourth, loosen the locknut on the full throttle stop screw on the throttle pulley, and back the stop screw away. Hold the pulley in full throttle position, noting that the butterflies are both full open. Adjust the stop screw until it just touches the pulley and retighten the locknut. This stop screw merely prevents stress on the linkage while the engine is at full throttle and the kickdown switch is in operation, and is not meant to restrict full throttle.

Ensure that the throttle moves freely through the full range of motion. Note especially that if the cruise control cable is too tight, it can restrict the throttle linkage moving fully to idle.

You will need to warm up the car and readjust the idle speed, since the butterfly stop screw positions have been altered.

THROTTLE STICKING: Apparently, all cars have occasional problems with throttle sticking due to buildup on the butterfly itself. A butterfly cleaning procedure from Randy Wilson: "You are cleaning the throttle plate and surrounding area. The edge of the butterfly and the area of the housing right around it will be covered in black goo. Prop the throttle open and wipe the stuff out with a rag. Use the weakest solvent you can to get it clean. I start with a "WD-40" grade oil, and go to carb cleaner if it's really bad. Oven cleaner is out. Sand blasting is not needed or recommended.

"Warning: Some non-Jag cars, notably later Fords, have a teflon coating on things in an attempt to reduce this problem. Most solvents will damage this coating."

THROTTLE LINKAGE LUBRICATION: Jan Wikström says, "The ball-joints shouldn't be lubricated at all, unless you want to give them a dusting with Teflon or graphite. The reason is that grease hardens and oil or grease picks up dust from the air, increasing linkage wear and friction.

The Fuel System is continued