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 "fuel injection 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. Sometimes the special clamps are offered in a package with
the hose; if possible, it is recommended that you get the package
that includes them, because it may be difficult to get suitable
clamps elsewhere.
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.
Compression Seals
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.
Clamping Hoses
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, about
20 gauge. Wrap the wire around the hose three times, closely spaced
and tightly, and then twist the ends together to bring it tight. When
done, cut off the extra and bend the tip of the twisted portion over
on itself so the sharp edges aren't exposed.
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.
Sources of Fuel Odors
There are a couple typical places to check for sources of odors.
Fuel-Soaked Carpet Foam
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.
Leaking Tank
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.
Tank Stress Cracks
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.
Rusting Fuel 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.
Filler Cap Connection
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.
Weeping Fuel Hoses
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.
Overflow Pipe
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.
Fuel Tank 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 1967 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 products
chemistry, but it dries to a white Teflon-like film.
Obviously, major cracks or holes will require more extensive
repairs.
Hess & Eisenhart Convertible
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 fuel system works, so a description is included here.
Fuel Tanks
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 Modifications
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.
Vapor Recovery System
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.
Overview
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 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. 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.
Breathing
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.
Recall Modifications
The original XJ-S vent system pretty simply followed the
description above. However, there were indications it did not work as
well as intended (including numerous complaints about fuel odors), so
there was a recall to address the system. As a result of the recall,
there are components of the system that are positively operated by
engine vacuum; in other words, valves that are opened when the engine
is running.
Canister Replacement
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.
Cannister Connections
The 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.
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.
Cannister Location
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.
Engine Fires
The early XJ-S 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's were recalled and the new system fitted -- if you still
have the old, see your nearest Jaguar dealer.
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.
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, causing vapor lock
problems. The cooler is to counteract that 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.
Convertible Fuel Cooler
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 Pickup Screen
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.
Idle Speed Adjustment
If you have a repair manual, you already know how to adjust the
idle speed. However, if you do not have a manual, you may make
incorrect assumptions about how to adjust the idle speed, so this
section is included to help prevent problems.
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 actually 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.
High Idle
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 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 2 inches
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.
Idle Stumble
The mid-1980's H.E. tends to "stumble" at idle when warm, even
when it runs perfectly smoothly when cold or at higher throttle. This
appears to be normal, although it is definitely disconcerting to an
owner that spent the kind of money this car costs and expects better
from his 12-cylinder engine. Fuel injector cleaning and/or
replacement, spark plug replacement, and oxygen sensor replacement
have no effect.
One Solution
The only suggestion that seems to have any significant benefit
comes from Chad
Bolles, who suggests disconnecting and plugging the vacuum line
to the right side fuel pressure regulator. This will cause the
regulator to open up, and the left side regulator will open up to
control rail pressure, so that the pressure is nearly unchanged but
the flow circulating back to the tank increases significantly. The
overall effect is minor, but it seems to reduce the stumble and
improve the throttle response somewhat. Note: if the left side fuel
pressure regulator is not connected directly to manifold vacuum, it
may not be wise to disconnect the vacuum to the right fuel pressure
regulator. One or the other of them must be connected to manifold
vacuum, and on some cars a temperature sensor in the fuel rail is
used to control vacuum to the left regulator to prevent problems with
hot starting.
Intake Manifild Leak
On the other hand, a stumble may be a sign of an intake manifold
leak. Since the EFI senses manifold vacuum and meters fuel
accordingly, it would make sense that an intake manifold leak would
only cause a high idle, not a stumble or misfire. However, a manifold
leak that is near the intake of one particular cylinder apparently
has more effect on that cylinder than on others, and can cause an
individual cylinder to run lean. This may be quite serious, since a
lean-running cylinder is a candidate for a dropped valve seat -- a
very expensive problem. If a leak is suspected, a can of WD-40 makes
an excellent leak locator; simply spray on each area while the engine
is running and see which spot makes a difference when sprayed on.
The gaskets between the intake manifold and the heads are common
leak sources. It appears to be necessary to retighten the
manifold-to-head nuts occasionally, especially shortly after a
reassembly. In fact, just go out to the garage NOW and torque 'em all down.
Throttle Linkage
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 or nylon bushing in the plate for the shaft to turn in.
If the original bushing was rubber, it's probably shot -- British
non-metallic parts again. This bushing will dry up, crack to pieces,
and fall out, leaving the throttle shaft to wallow around in the
opening. 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.
The part number for the original Jaguar rubber bushing is C34388.
Substitute Parts
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 nylon
bushing to use here. Retention isn't a problem since it is
effectively trapped; a bushing with a single lip will work.
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.
Replacement
Yes, replacing this bushing is as difficult as it looks. It
requires removing either the throttle body or the linkage support
plate, either of which is a pain. If you choose to remove the linkage
support plate, it will permit you to fiddle with the bushing
installation away from the car -- or take it with you when shopping
for a generic bushing.
After replacement, the linkage should definitely be adjusted as
described below.
Throttle Linkage
Adjustment
If the butterfly stop screws
have been disturbed, the linkage should be readjusted as follows.
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. 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.
Check Cruise Control Cable
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.
Adjust Idle Speed
You will need to warm up the car and
readjust the idle speed, since
the butterfly stop screw positions have been altered.
Fuel Injection System Types
The 1976-80 XJ-S used a type of fuel injection system based on a
Bosch "DJetronic" design. From 1980-on, the cars used a system
referred to as a "Digital P" also Bosch. The two systems are
completely different. Among the differences: The earlier DJetronic
system used a trigger board within the distributor operated by a
magnet in the rotor; the later Digital P system simply derives its
triggering from the ignition wiring. The DJetronic has a "throttle
switch" in the bellcrank on top of the engine that provides an on-off
pulse about ten times as the throttle moves from idle to full open;
the Digital P has a "throttle potentiometer" in the same location,
providing a smooth varying resistance as the throttle moves. The
DJetronic has no oxygen sensors, while the Digital P has two.
One more notable difference: The fuel regulators on the DJetronic
system maintain the pressure in the fuel rail at a constant value,
while the regulators for the Digital P system vary the pressure
according to intake manifold vacuum.
Unless otherwise noted, the descriptions here refer to the Digital
P system, because that's what's in the author's car!
According to Dick White,
There is a book 'Bosch Fuel Injection and Engine Management'
which I found very informative. It contains many references to
Lucas.
It is available from EWA &
Miniature Cars USA, INC among other sources.
D-Jetronic Information
For those with the DJetronic system and who have access to the
World Wide Web, Ray Reynolds reports there is a site providing info
on the system at www.estinc.com/porsche/djet.html. It is maintained
by Porsche drivers, but the EFI systems from that era were similar.
Checking Digital P Systems
Michael Neal sends this info on checking the Digital P EFI system:
Monitoring O2 sensor feedback voltage just lets you
know the EFI is in closed loop operation. This should be checked with
a HIGH input impedance digital volt meter. A
cheap meter will fry the system. Check the voltage at the
O2 sensor connector with the sensor hooked up and the
engine running. The voltage will fluctuate from 0 to 1 volt. With a
fairly fast updating meter you should get a voltage swing of at least
0.3 volts. A 0.1 or 0.2 volt swing shows a problem with the
O2 sensor, open loop operation, or a problem with the
sensor driver in the ECU.
Verify the car is going into closed loop which is the 0.3 V or
more swing. If it is then you need to check the injector duration.
Most good meters have a duty cycle or millisecond pulse duration test
feature to them. The pulse duration should be around 3
milliseconds.
Robert Dingli says:
It is pretty obvious when the system goes into closed loop
control. While the open loop controller may be tuned to near lambda =
1 (relative air/fuel ratio where 1 equals stoichiometric mixture) the
voltage output will 'flicker' around 0.5V or else sit at a low or
high output. When under closed loop control, the perturbation due to
the closed loop system can be clearly seen as a low frequency
oscillation in the output.
Injector Fuel Supply
It is also 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.
Dingli also suggests:
An oscilloscope or a smart DVM with pulse width or duty cycle
readouts can be used to check the injector electrical supply. Some
modern ECU's can detect whether an injector is unplugged (or short
circuited) and thus it's best to connect the electrical apparatus in
parallel with the injector.
The wiring harness is set up to operate the injectors in four sets
of three. However, within the ECU these circuits are combined to form
two sets of six. Reportedly, in the early D Jetronic systems, each
set of six injectors includes three on each bank. However, in the
later Digital P systems (which include oxygen sensors), each group
includes all six injectors from a single bank.
Open-Loop/Closed-Loop
Operation
On the Digital P system, the starter inhibit switch is also
connected to the EFI system. In Park or Neutral (starter permitted),
the EFI operates in an "openloop" control mode, where the oxygen
sensors are ignored and the EFI controls to a fixed fueling map. When
in Drive or any other moving gear (starter inhibited), the EFI
operates in "closedloop" mode, adjusting the fuel mixture to obtain
the correct oxygen sensor feedback.
For those of you who are subject to emissions testing, you should
be aware of this. To put the EFI into closed-loop mode even in P or
N, you must pull a shorting loop from a connector near the ECU in the
trunk.
Grounding Problems
Michael Neal sends this experience:
...the radiator had been replaced and a ground for the fuel
injection harness at the right front of the engine compartment had
not been resecured. It had blown two ECUs before I found this. I
don't know why but it took the ECU a week or two to blow. After I
replaced the ground and ECU there were no further problems.
Reportedly, if the engine clearly is running very rich or possibly
won't even start because it's too rich, it's time to start looking
for grounding problems in the EFI wiring. John Napoli relates one
experience:
Although ground to the ECU was one of the many things we had
checked early on, the owner later went further and checked the ECU
connector. He found an intermittent ground on pin 1 at the connector.
This pin, according to our schematics, should ground to the frame of
the car at the ground points near the battery. This wire was
identified in the loom and a splicer to ground added. The car started
fine and at this point is OK.
EFI Electronic Control Unit
Jeffrey Gram reports that he called AJ6 Engineering and got the
following part numbers for ECU's:
|
These are the low compression version -- presumably
11.5:1
|
|
Pre HE:
|
Type 3CU
|
No part numbers supplied. This is actually a Bosch unit,
but labeled as a Lucas.
|
|
HE:
|
Type 6CU
|
Catalyst version: DAC 2597 and DAC 3586. Non-catalyst
version: DAC 2596 and DAC 3062
|
|
|
Type 16CU
|
Catalyst version: DAC 4118, DAC 4585, DAC 335 and DAC
6337
|
|
These are the high compression version -- presumably
12.5:1
|
|
|
|
Non-calalyst version: DAC 4119, DAC 4478, DAC 4586 and
DAC 6336
|
|
Additionally there is a low compression non-cat version
DAC 6338
|
Troubleshooting
The people at John's Cars say
they will test your ECU for you, free of charge. They are confident
you will eventually be buying something. They add, however, that
since testing requires a car, there may be a few days' delay until
they have a car with the correct system on hand for the testing.
Of course, you can probably learn a lot yourself if you have a
friend with a car similar to yours. Swap the ECU's and see how many
problems go with them.
Andrew E. Kalman sends this tip:
I suggest you put a VOM on the breakout connector (it has a
wire "loop" on it) that comes out of the ECU. The outer two pins are
Vcc and GND, and the middle two should be rocksolid at 2.500V when
idling. These test points (you can see them on the XJ-S FI wiring
diagram, the one with the injectors, relays, sensors, etc.) seem to
indicate whether the two "banks" of electronic control for the motor
are operating properly.
Substitutes
If your ECU gives up the ghost, please see the comments under
Engine
Modifications before spending the major $$$$$ for a new one.
Also, you might want to contact AJ6
Engineering or Corsaro
Electronics.
If you wish, you can open the ECU easily enough; it is a simple
cover-body-cover sandwich with several screws holding it together.
Note that a couple screws have aluminum caps that serve as a tamper
indication; it might be wise to inquire about policies regarding
exchanging an opened unit before opening.
Take precautions to avoid static electricity discharges while
inside this unit. Usually, it is sufficient to keep one hand on the
chassis while working.
ECU Internal Connections
The harness connects to the ECU with a 35-pin connector. However,
within the ECU itself, many of the wires from the harness are simply
connected together. When trying to figure out how things work, it may
be helpful to know what wires are connected internally. To save you
the trouble of opening it up to see, I will provide the info here
based on the ECU in my 1983 (part number DAC 2597). The following
groups of connectors are all wired together inside the ECU:
|
1-2-19
|
(ground)
|
|
8-9-27-28
|
("B" bank injectors - open)
|
|
11-29
|
("B" bank injectors - hold)
|
|
12-30
|
("A" bank injectors - hold)
|
|
13-14-31-32
|
("A" bank injectors - open)
|
|
16-17-34-35
|
(ground)
|
On the schematic in my repair manual, I have drawn boxes around
each of these groups to remind me of these internal connections.
EFI Wiring Harness Troubleshooting
Matthias Fouquet-Lapar suggests
One thing I would do is to put in fixed resistors for the
various sensors direct at the ECU connector to find out if there's a
problem in the harness.
Fuel Injectors
If your engine is running or idling rough, one possible problem is
a plugged or bad fuel injector. This may be indicated if the misfire
always seems to be the same cylinder, although a bad spark plug or
wire or mechanical problems in that cylinder are other possible
causes. One-cylinder problems have different symptoms than they would
have on a carburetor system, because a misfire in one cylinder causes
the fuel and oxygen to enter the exhaust unburned. The oxygen sensor
will pick up the excess oxygen, and the ECU will conclude that the
engine is running lean. The ECU will then richen the mixture to all
12 cylinders, and then all cylinders sound bad, not just one.
Troubleshooting
If you suspect there is a problem with an injector, there are
several steps to take. First, check the windings for shorts with a
VOM. According to the Special Interest
Car Parts catalog, the windings on an injector should measure 2.4
ohms at room temperature, and must not be shorted to the injector
body.
Next, purchase one of the many fuel injector cleaners available
that can be added to the gas tank.
If that doesn't fix the problems, the next step is to take the car
to any place that specializes in fuel injection work. They can flush
the injectors with a cleaner by just connecting a line to the fuel
supply line and running the engine.
If this doesn't work, the next step is to depressurize the fuel
system, disconnect the supply and return hoses, remove 24 nuts and
remove the rack of injectors as a unit. Take it to the same fuel
injection shop and have them flush it in a rig. With it separate from
the engine, they can use much more powerful cleaners than they can on
the engine. Best of all, even if their cleaning doesn't fix the
problem, they will be able to tell you if any injectors are bad and
which one; they can actually watch them spray on the bench.
Testing Them Yourself
If you're the adventurous type, you might try testing the
injectors yourself. Unbolt the set from the engine and raise them up
a few inches while leaving the fuel supply and return hoses
connected. Jumper the relay in the trunk to allow operation of the
fuel pump with the engine off. IMMEDIATELY
check that no injectors are dribbling fuel. Place a small glass jar
around one injector. Connect a couple wires to this injector, and
give it a quick zap with 12 volts. Note: do not leave 12 volts
connected continuously; only give the injector instantaneous jolts.
Observe the performance of the injector. Repeat for all injectors;
you can empty the glass jar back into the tank between tests.
Obviously, any injector that seems to perform differently than the
others is suspect. No smoking is suggested during this procedure, and
it would also be wise to avoid electrical sparks.
The injectors can be replaced individually, and there is nothing
wrong with replacing only the one that's gone bad. Replacing the
whole set is expensive, and not warranted.
The only differences between injector part number 0 280 150 163
(1985-on front two), and 0 280 150 164 (1985-on rear ten) is the
length of the piece of hose attached to them. These injectors were
fitted as a recall to cars with injector part number 0 280 150 105
(1980-85), so it's unlikely these injectors have any functional
difference either.
Note, however, that the DJetronic had different injectors; the
earliest cars had 0.023" injectors while the later had 0.035"
injectors, indicated by the last three digits of the part number:
73143A/0 280 150 023 or 73143B/0 280 150 035. Reportedly, the 0.023"
injectors can be retrofitted with the 0.035" injectors as a set, but
replacing individually is not recommended.
Fuel injectors tend to be blamed for a lot of problems, probably
more than they actually are responsible for. Michael Neal (Jaguar
mechanic) says:
The only failed injectors I have seen have been from running
water through them or running a car with a blown head gasket to
death.
Noisy Fuel Injectors
Hunt Dabney says:
On the noise issue, I just replaced all of the injector seals
and rubber mounts. My injectors are now really quiet!
Frank Perrick says these seals are available at any auto parts
store since they are standard Bosch items. The seals come in packages
to service four injectors, "4 fat ones for around the body 4 tiny
ones for around the nozzle." Beck/Arnley # 158-0021 vp 1, although
you can just carry an injector in there and say "I need these
gaskets."
Throttle Potentiometer
(Digital P)
If your XJ-S has ragged throttle response as though it has a bad
accelerator pump, here's some news for you: it doesn't have an
accelerator pump. However, the throttle potentiometer, located
underneath the throttle pulley on top of the engine, can cause
similar symptoms when bad. When operating properly, the resistance
across this pot varies smoothly as the pulley is rotated. If it is
breaking up, it confuses the EFI computer on accels. The EFI
computer, using inputs from the oxygen sensors, can usually keep the
engine running reasonably well at constant throttle, but it stumbles
during throttle changes.
The original Jaguar pot is both unreliable and expensive. Sounds
like a Lucas part.
Repairs
If you wish to attempt to repair the potentiometer, Matthias
Fouquet-Lapar sends a procedure:
Carefully undrill 3 plastic melt points from the bottom. After
about 2 mm you'll see a screw. Using a small screwdriver undo these
screws.
Open the potentiometer. It's actually a very good quality pot,
(double contacts), but clearly showed excessive wear on light part
throttle position. Using my VOM I could find several places where the
carbon really had gone away.
Mmmmh. I decided to cut off the 4 contacts, shorten them by
about 1 mm and resolder them so they would end up on the unworn
surface. This is a pretty sensitive operation, be sure that you feel
confident that you can handle it. You need some good small tools, a
fine solder iron, some PCB cleaner AND a very
quiet hand.
Resolder everything, adjust contact height as before to have
the correct pressure when putting it back together. Also check if the
contacts are really off the worn track.
Put it back together, check again with a VOM. Smile, since you
just saved a bunch of money.
Total repair time was about 2 hrs. However, I think one can do
this kind of repair only once, or maybe a single contact could be
used instead of two, giving a potential of a third repair.
Another possibility is using a pot from another type car. Brian
Sherwood relates his experience:
From my spare parts pile I found a TPS from a Ford, a 1983 3.0
liter V-6 I think; part number E7DF-9B989-AA. It turned in the proper
direction, same degree of travel (90 degrees), and had the same
resistance as the original at both ends of it's travel (from .05 to
3.5K ohms). But no, it doesn't bolt right up. I cut a slot in a steel
bushing to fit the drive lugs inside the Ford TPS. The other end of
the bushing I crimped down to fit the D shape of the shaft on the
bottom of the throttle pedestal, that the old TPS used to fit over. A
piece of aluminum strap was used to clamp the Ford TPS to the bottom
of the pedestal. The TPS fits snugly in the recess underneath, and
loosening the strap allows adjustment. I cut the wire and plug from
the old one, crimped on some female spade lugs to fit the terminals
of the Ford unit (would have been neater to use the proper Ford plug,
too, but I couldn't find that.) Red wire=wiper, green=high side of
pot, yellow=low side of pot. With new TPS plugged in and ignition on,
I adjusted the TPS to give 0.36 volts measured between red and yellow
wires, at idle position. Bolted everything down, and went for a test
drive -- worked great. Only difference from the original is that now
it doesn't surge at cruise anymore!
I expect a new Ford TPS would cost about US$30 if you bought a
generic one. There might even be something out there that would fit
better, this was just convenient for me.
Throttle Potentiometer Adjustment
When you replace the throttle pot, the Jaguar manual says you must
adjust it using their special electronic tester. Below is the
alternate method.
The throttle pulley assembly must be unbolted from its tower to
adjust the pot, meaning the linkages to the butterflies are
disconnected; but the idle stop is part of the throttle pulley
assembly and therefore is unaffected. You can even start the engine
in this condition, as long as you don't go above idle.
Have the ignition on, and the throttle pot assembly rotated to the
idle stop. The engine may be running or not. Connect a digital
voltmeter (the old needle type just won't do -- go to Radio Shack and
fork over the US$40) to the red and yellow leads from the pot without
disconnecting the pot from the harness. This can be done by pushing
the probes under the insulation on the connector.
Adjust the pot by loosening the three small mounting screws and
rotating the pot until the voltage reading is within 0.32 to 0.36V.
Tighten the mounting screws and reassemble. Make sure the reading
remains within limits when the linkage is all together and the engine
is running at idle.
Oxygen Sensors
When the indicator on the dash tells you to, you probably should
replace the oxygen sensors. They are critical to the correct
operation of the EFI.
The oxygen sensors are available at local parts stores. There is
no need to insist on a Jaguar part; a generic replacement sensor will
work fine; Brian Sherwood suggests Bosch universal sensor p/n 11025
for the earlier non-heated sensor. The sensor for an XJ6 can also be
adapted. Take an old sensor in with you (if possible) to make sure
the new ones are the right thread, etc. Don't worry if the fluted
sensor portion doesn't look exactly the same. If the wire is the
wrong length or has the wrong connector on the end, use a crimp
connector to connect the new sensor with the wire cut off the old
sensor. Soldering is not recommended, as this wire may see
temperatures high enough to melt the solder.
Resetting the Dash Indicator
The dash indicator doesn't tell really tell you that the sensors
are bad; merely that they've been in there a specified time, around
60,000 miles. There are even reports of the sensors failing before
the counter turns the indicator on. The counter is in the trunk,
hidden on the left side near the filler cap. The little plastic box
has a small opening through which you can poke a pointy object to
reset the timer to zero when you replace the sensors.
Testing the Sensor
Motor/Age Magazine gives the following instructions for testing an
oxygen sensor itself:
An oxygen sensor can be tested safely with a digital voltmeter,
but an analog (needle type) voltmeter will destroy the sensor in a
heartbeat. A simple bench test has been suggested by Tomco
Carburetors to check O2 sensor function. All you need is a
vise, digital VOM and a propane torch.
Lightly clamp the oxygen sensor in the vise with the sensor
flutes facing upward. Attach the digital VOM leads to the sensor. If
the sensor only has one lead, attach the VOM ground to the sensor
body. Set the VOM on the 2 volt scale, then light the propane torch
(using regular heating tip) and apply direct flame to the tip of the
sensor flutes. The voltage should rise to about 0.8-0.9 volts within
60 seconds. Move the flame away quickly from the sensor tip and the
voltage should drop drastically; move the flame back and forth and
the voltage should respond quickly. If the changes aren't almost
instantaneous, it's time for a new O2 sensor.
The later XJ-S reportedly comes with an oxygen sensor with a
built-in heater to bring it up to operating temperature faster. These
type sensors are considerably more expensive than the earlier ones,
but they still are available as generic Bosch parts; paying Jaguar
dealer prices is not necessary.
Air Temperature Sensor
The official XJ-S Repair Operation Manual, section 19.00.07, has a
chart of air temperature vs. ohms for the purpose of checking the
sensor mounted on the left air filter housing. If you have sensor
part number 73197 (Digital P systems), this chart is incorrect;
it may apply to D-Jetronic systems. The correct resistance for this
sensor at room temperature is around 2,800 ohms.
Water Temperature Sensor
According to the Jaguar literature, the water temperature sensor
provides a "minor" trim to the fuel schedules. However, when the
sensor fails, the trim can easily become major. If the EFI thinks the
coolant temperature is -60°F (or some such ridiculous value),
it's gonna be overly rich and have trouble starting.
Michael Neal sends this info:
XJ Late EFI Coolant Temperature Sensor Data Chart Created
06/24/94
Negative Temperature Coefficient Thermistor
|
°C
|
°F
|
Resistance (W)
|
|
-10
|
14
|
9200
|
|
0
|
32
|
5900
|
|
10
|
50
|
3700
|
|
20
|
68
|
2500
|
|
30
|
86
|
1700
|
|
40
|
104
|
1180
|
|
50
|
122
|
840
|
|
60
|
140
|
600
|
|
70
|
158
|
435
|
|
80
|
176
|
325
|
|
90
|
194
|
250
|
|
100
|
212
|
190
|
Don't use Lucas brand. Get a Bosch part, cheaper and better.
This chart applies to 1979 and later fuel injected Jaguars. All the
same.
Trigger Unit (DJetronic)
The trigger unit originally fitted inside the distributor has a
three-wire connector that plugs into the EFI wiring harness. However,
the replacement trigger unit has a fourth wire, separate from the
connector; three-wire units are no longer available. The fourth wire
must be connected to a 12V power source that is switched with engine
ignition. Apparently, the early trigger units consisted of reed
switches while the replacement unit works by Hall effect switches,
and the Hall effect switches require a power supply.
Reportedly, the official Jaguar procedure is to connect this wire
to the white wire at the ballast resistor. This, in fact, should
provide the proper switched 12V source -- on paper, anyway. However,
Ray Reynolds reports that the 12V available at the ballast resistor
was so noisy that it caused the injectors in his car to fire wildly,
resulting in flat spots and even stalling at some throttle positions.
He simply reconnected this wire to a more reliable 12V source and his
problems cleared up.
Jan Wikström:
The manual says it has reed switches, but my two (1977 and
1978) have Hall effect switches and the test procedure in the
workshop manual doesn't work.
Cables
Vince Chrzanowski sends this report on a problem with his car:
It seems that the engine revs information is sent to the ECU
from an amplifier unit atop the engine. The signal is sent via a thin
shielded wire. Unfortunately, the wire is routed near some very hot
areas and that heat melted the insulation between the center
conductor and the shield, shorting the signal to ground. Replacing
the defective section of wire restored the signal. In talking with
some other local Jag owners, I've found that this is not an unusual
problem.
Intake Manifold
Shortcomings
Bill White, an expert on the Helmholtz theory of intake manifold
design, notes that the intake runners to the corner cylinders on the
Jaguar V-12 are longer than those serving the center eight cylinders.
He performed single-cylinder rig tests on the different runners and
found that, at the tuned frequency of the manifold, the corner
cylinders produced 8% more torque than the other cylinders. This
means that these corner cylinders are getting a larger charge of air
than the others.
If this were a carburetted or throttle-body EFI engine, this
wouldn't really make much difference. However, being a multi-port
EFI, each cylinder gets the same amount of fuel. Since these corner
cylinders are getting more air, they are running leaner than the
other eight.
What can you do? Probably not much. If your system has oxygen
sensors, they will sense oxygen from the leanest cylinders and
control the fuel supply to maintain stochiometric there; the other
cylinders will simply run a little richer than stochiometric, which
shouldn't hurt anything except a little fuel economy and emissions.
Passing Emissions Tests
If your car is too old and tired to pass a required emissions
test, you should have it corrected. However, if you don't have the
time or money to get this done right now, John W. Himes makes the
following suggestion:
I add a gallon of denatured alcohol to the tank. This makes a
very clean burning fuel. The car does not run as good with that in
the tank, but it passes emissions very well.
Alcohol tends to be hard on some rubber products in the fuel
systems of earlier cars, and British non-metallic parts have enough
trouble without adding to it. Therefore, it is not suggested that you
use this method more often than necessary.
On to the Exhaust
System
View the latest posts from our Forums via an RSS Feed!
