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Michael Neals Technical Advice Main / Library / Technical / Model guide / Buyers guide / Guestbook / Photobook / Links / Archive / Specialists

Michael Neals Technical Advice : File 3

XJ6 Series 3, Ignition, Coil

A leaking coil brought an important issue to mind.
At VIN 412543 on North American XJ6s Jaguar found fit to change to a ballast resistor type coil along with a revised amplifier and harness. Note that the ballast resistor is not a bypass resistor! It is always inline to the coil. The coil is French made Ducellier with a Unipart label stuck over the top of it. They are prone to leakage and are often replaced with a cheaper unit. Jaguar retails the proper unit at around $130. The only reason that I have found so far for the coil change is to protect the amplifier by limiting the input voltage to the coil. Unless you are willing to take a good chance of spiking your ignition amplifier I would recommend using the expensive Jag unit. Several people on the jag-lovers mailing list have used aftermarket coils and rigged an external ballast resistor. So far there have been no problems so this does seem to be a viable alternative.
Usually the culprit in a spiked amplifier is a faulty distributor pickup. Always replace the pickup if the amplifier is blown. I had several cars come back with the amplifier blown after a initial replacement. Did some checking in the service records and found that almost every car that only had the faulty amplifier replaced came back for another. I even found one that had three amps in 5 years. Now that I've been replacing the amps and pickups as a pair I have had no returns!
A word of warning on leaking coils. The oil may contain PCPs which are very hazardous to your health! Wear latex gloves like the professional Jag techs do. Good quality latex gloves are available for around $5 a box. A very necessary accessory for working on your oily Jag.

XJ6 S3, Dash, Ignition Buzzer Disabling

Near the ignition lock area there is a two wire connector that will disable the little bastard when disconnected. There is a switch in the ignition lock that activates the buzzard and it sometimes will stick.

XJ6 S3, EFI, No Start Troubleshooting

Check the fuel pressure at the feed line to the rail. It should be around 30-35 psi. Check for power to the injectors by backprobing any one of the injector connectors on the rear wire. Check the fuel pump contact in the air flow meter by turning the key on and operating the flap inside the meter. The fuel pump relay should click and the pressure should go up. You may be getting spark but at the wrong time. Remove the reluctor wheel in the distributor and check the plastic retaining ring. They have a tendency to disintegrate over time. Proper injector signal can be checked using a pulse duration meter, a good shop should have one! In absence of the meter use a noid light available from your local automotive tool dealer, just a few bucks. Check pin 1 on the ecu while cranking for the engine speed signal. At idle it is 9.5VDC, cranking should be significantly lower.
Check the injector grounds. There are grounds on the intake manifold at the rear that have a jumper strap to the head. Check the connections at the injector power resistor pack. It is mounted near the front of the inner fender on the right side. Pull the connector, crimp the connections tighter and reinstall. This unit must have a good ground.

Various Information, Dealers

Seeing that I have dealer experience as a tech let me throw in my two bits worth.
I went into the dealer as an apprentice. I had an accelerated apprentice program that I finished in two years. I worked there for another three and gave it up due to a 80 minute commute each way. I went to work for a shop that worked on all types of British cars. I specialized on '80 and newer Jaguars. I had made an investment in time and tools to work specifically on the late Jags and stuck to them. Specializing on a particular group of cars allowed me to go more in depth on the various systems the cars use.
The dealer I worked for, San Francisco British Motors, was the dealer that really started the British car importation in large numbers back in the fifties and early sixties. You would think with this kind of history it would be one of the best. Not true. At least half of the techs there could care less about Jags, they were there only for a job. The main training school was in nearby Brisbane but was moved in the early 90's. Rather than travel to L.A. to the relocated training facilities many of the older techs refused to go. I took advantage of this and fit all of my training schools into one year. The classes were taught by professional technical instructors that had no real world Jag experience. They were real basic and didn't offer much even though they were model specific. They did, however, give me a basis for my in depth probings.
Jag school gave me insights into how other dealers worked. I visited most of the dealers in the L.A. area. Some were a bit better, some were worse but they got the job done. I've seen a few dealers that have Jaguar as a sideline with a couple of techs. I don't recommend going to them. It is important to go to someone who only works on Jaguars!
With the advent of the XJ40 in '88 the level of technology in the car tripled. The techs skills didn't increase and many were left in the dust. In ten years most techs aren't going to have any idea of what is going on and will be working at quik-lubes. The reputation of mechanics is well deserved. As a group the level of intelligence is not the highest. For example; there is a Automotive Service Excellence certification that shows you have a certain skill level and understand basis theory. The government wants to require this testing. The automotive industry says they can't do this because they would have to make the tests too easy to let everybody pass. This shows what kind of thinking is going on. I passed all these tests when I was a first year apprentice and gained Master status. I constantly upgrade my education, most techs don't.
You will usually pay more to take your car to a specialty repair shop. Whether it be a Jag dealer or a Jag Independant, pay it! There knowledge base about your car is much bigger than the local "we fix anything" shop. These fixit shops are on the way out anyway, the technology advancements are forcing everyone to specialize whether they like it or not. I've got tons of horror stories about fixit shops repair jobs on Jags. Many times they even charge more than the local Jag indepentant. However, dealers are not the cure all. It depends on who is working on your car. You are better off finding a tech from the dealer that does work on the side if you are really worried about cost. Most of the time your car will never be worked on by the same tech at the dealer. I've seen cars bounced around and never really fixed. Bottom line, find someone who works only on Jags and really has an interest in them. Pay their price if they know what their doing. If you can't talk to the guy who actually does the work then you are quite a bit more trusting than I am.

XJS Engine, Mechanical, Oil Filters Sizes

Jaguar supplied the XJS with the long filter from at least 82 to 93. In 93 a short filter was implemented that allowed more clearance with the bottom pipe of the convertor. There were excessive warranty claims for realignment of the exhaust to allow oil filter clearance, i.e. flat rate wallet padding. With Ford's acquisition of Jag the belt was tightened a bit.
The latest factory short filter has the flats on the top to allow the use of the end cap type oil filter wrench.

XJ6 Series 3, Engine, Mechanical, Damage Control

I've had a-lot of experience with damage control on the 4.2. Generally, when a Series 3 gets to 120 to 150 thousand miles it is due for a minor overhaul. I can usually get away with replacing the bearings. Cylinder wear is almost always minor, usually 1-2 thousands wear. Using a slow drill and a hone I can usually take out the uneven wear and put a nice crosshatch in the cylinder. The cylinder walls are a hard cast iron and take abuse with little damage. If there are any vertical score marks then the block gets bored. If you don't have to bore the block you can do all this in the car. I generally put new pistons in to take up the skirt wear and have the rods rebushed. If you are serious about saving money then bead blast or knurl the pistons to increase their O.D.. They won't last as long but they will function for a while. A piston knock can be very deceiving and you may not realize what it is a few years down the road. .002 wear is on the far limit but it may work. Jag's recommended clearance is .0007 to .0013 so .002 is out of their limit. It's going to be a gamble.

Generic oil change franchises

You went to a generic oil change frachise? Do you value your car? Those places are for those Japanese appliances on wheels. Would you like fry's with that, sir? Stay away from those places. There is a lack of connection between the wrench hand and the brain. You think any of these people actually care about cars? Take you car to a place that is familiar with your particular make and get your servicing done right. You'll end up paying for any money you're saving in the long run.

Series 3, XJS, Differential, Servicing

There should be no problem getting the fill plug out. If it is the square protruding type an 8 point 1/2 socket on a universal joint should do the job. In a pinch a 5/8 twelve point universal socket will also work. Otherwise it is the 1/2 square recessed plug and can be removed with a 1/2" universal fitting.

XJ, EFI, Coolant Temperature Sensor

XJ Late EFI Coolant Temperature Sensor Data Chart
Created 06/24/94 Updated
Negative Temperature Coefficient Thermistor
Deg C  Deg F   Resistance 
-10    14      9200 
  0    32      5900 
 10    50      3700 
 20    78      2500 
 30    86      1700 
 40   104      1180 
 50   122       840 
 60   140       600 
 70   158       435 
 80   176       325 
 90   193       250 
100   212       190        

XJ6 Series 3, Body, Spare Key

Not only did Jaguar think of everything and put access holes under the hood latches they also fastened a spare ignition key where the body brace on the left side anchor near the left fender. I've actually seen the key still fastened in it's original position.

Series 3, EFI, Smog Test Failure

First of all, theory from a bosch book may be fine but it won't get you too far in the real world. Remember that this is a Lucas system licensed from Bosch. It's got it's own idiosyncrasies, british engineering is involved.
The last thing you want to do is mess with the air flow meter internal adjustments, it won't actually fix the problem but might temporarily . It may work on BMWs, etc but it will not help a Series 3. Remember that there is a problem with the system and modifying the symptoms will not cure the cause.
Without a CO, HC meter you can not accurately set up the car! 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. The voltage will fluctuate from 0 to 1 volt. With a fairly fast updating meter you should get a voltage swing of at least .3 V. A .1 or .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 .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. I'll have to check the duty cycle reading, I don't normally use it. If your injectors are firing right then there is a high probability of a mechanical problem. In the meantime do a quick visual check.
A basic visual check should start with all grounds and connectors. Make sure the grounds are secure and none are missing. A common missing ground is the small strap from the intake manifold to the cylinder head.
Disconnect all EFI connectors and reconnect, including the ECU in the front part of the trunk. Check distributor position, vacuum advance pot intake should face the rear of the car. Timing should be at norm or at most 3 degrees retarded. Smog checks will fail a car if the timing is advanced over the specified setting. It can be retarded as much as you like as long as it passes the tailpipe test.
If you've made it this far through the message you must be interested! If you are Tom Graham let me know exactly what the emissions readings were, including O2 and CO2. I may be able to tell what your problem is if I've run across it. I keep an extensive tech data base so it may in there.
The majority of the S3s left the factory with the idle air bleed on the air flow meter turned six turns out from the bottom. If a car is running properly I can usually set them up to that point and get normal readings.

XJ40, Hydraulics, Warnings

The XJ40 hydraulic system can work properly if failed components are replaced. I see more early XJ40s bouncing and knocking down the road because their owner's have given up on the system. Does anyone have any hydraulic problems, low brake pressure lights on, or a hard brake pedal. Give me a place to start and I'll explain the system and how you can fix your problem.
Your XJ40 has a rear strut that uses a nitrogen bladder for dampening and hydraulic fluid to push on that bladder to raise the car. Jaguar has finally given up on this system after years of trying to get it right. The nitrogen bladder is ruptured on your car and you are no longer getting the dampening effect. The struts need to be replaced with the non ride leveling type. There are two ways to do it. Use the original springs or the springs Jaguar used specifically to do the conversion. Using the original springs will save you a couple of hundred dollars with a slightly stiffer ride than the conversion springs would give.
Jaguar is now offering a kit to update the hydraulic struts to standard shocks. The charge solenoid is also probably faulty and will need to be replaced. It also controls the charge of the brake system so it is necessary to make sure it is ok. I can also get parts at a pretty good discount so let me know if you are going to go ahead and fix the car. The struts are only used on the XJ40 so you S3 and XJS owners can relax!

XJS, Engine, Mechanical, HE Cylinder Heads Grenading

I've seen many HE engines dropping the valve seats. The car cannot be overheated without the severe damage that results from a displaced valve seat. Sometimes the damage can be caught but usually the owner just keeps on driving and wonders what the loud tapping noise is. The valves are surprising hardy, I haven't seen one break a head off yet. The seat, however, is the weak link and is quickly turned into shrapnel. The shrapnel then goes into the manifold and is sucked into the companion cylinder.
I've seen this first hand more times than I would like. I've gotten to the point of thinking of installing an engine shutoff device that reacts to heat. It is also very important to clean out the intake manifold before reinstalling.

XJS, High Idle

Make sure that the engine is warmed up completely. Turn the idle air volume adjustor bolt all the way in. This is located on the extra air valve on the left rear of the motor. Check the flow of air at the hose from the back of the left air cleaner to the extra air valve. Remove the air filter and leave the air cleaner in place with the air temp sensor hooked up. Reach in and you will see the port that the hose connects to. Theoretically there should be no flow through this hose if you followed the steps above. However, I have seen a slight amount of flow on a perfectly working system. If the system is not working the air flow will be quite noticeable. If so then the thermostatic valve in the extra air valve is not working.
> Make sure that the engine is warmed up completely. Turn the idle air
> volume adjustor bolt all the way in. This is located on the extra air valve
> on the left rear of the motor. Check the flow of air at the hose from the
> back of the left air cleaner to the extra air valve. Remove the air filter
> and leave the air cleaner in place with the air temp sensor hooked up.

>Reach in and you will see the port that the hose connects to.

Could you please elaborate on the above statement?
I can,t visualize this step.

>>> Open the left air cleaner and remove the filter. Leave the air cleaner
>>> open and keep the air temp sensor hooked up. Near the back of the air
>>> cleaner housing is a port that has a hose that goes to the extra air
>>> valve. Check for air flow at the port with the bleed screw on the side
>>> of the extra air valve closed down completely.

>>> So...
>>>Theoretically there should be no flow through this hose if you followed
>>>the steps above.

Is this pointing out some left right cylinder bank mismatch?

>>> This valve allows air to flow to the balance tube and bypass the
>>> throttle butterflies. This controls the idle speed.

>However, I have seen a slight amount of flow on a perfectly working system.
>If the system is not working the air flow will be quite noticeable. If so
>then the thermostatic valve in the extra air valve is not working.

My V12 seems to be breathimg heavier on the right side than on the left. The intake at the right air intake trumpet is far greater than at the left. There is nothing obvious like block filter or something. I assume the left side breathing through the balance pipe that interconnects the inlet manifolds. What do you think? Bruce Hayes ( )
>>>I've never really checked the flow from one side to the other. I'll try
>>>to check an S tomorrow with a unisync.

I checked an XJS with a UniSync gauge and found equal airflow from one air horn to the other. A good check for vacuum leaks is to use propane. A small handheld torch is the way to go here. A word of warning though. If you find a bad intake gasket seriously consider not driving the car until it is repaired. The XJS I purchased was the victim of such circumstances. The one cylinder ran lean until it dropped the valve seat.
I suggested using a small propane torch to check for vacuum leaks. Of course it is necessary NOT to light it, just use the propane gas. This also works great for checking the injector seals. Get someone to put their hand over the exhaust and while you direct the propane at each injector have them feel for the exhaust pulses to smooth out. I've found that injector seals are a prime cause of a rough idle on an XJS. It doesn't really show up on an ignition scope either.

Various Information, Horsepower to Kilowatts

A while back someone wanted to know the conversion of Kilowatts to Horsepower. 1 Horsepower is 746 Watts so figure from there.

XJ6 Series 3, XJS, Cruise Control

Somehow I knew that if we left Tom Graham to his own devices that he would answer his own cruise control question. I chose not to answer because it usually isn't cost effective to mess with the check balls in the turn signal switch. Anyhow, I hadn't yet torn a cruise set switch apart yet. I did find an important piece of info from Tom's dissertation. The stalk must be grounded. I checked all my dead switches and found that the stalk grounding was the problem on every one!!! I wasn't about to invest the time in the teardown of the switch so I came up with a way to give it a quick fix. Simply strip the insulation on a 6 inch piece of wire and split the strands into two groups. Remove the bottom cover of the steering column trim and look at the base of the stalk. Put your section of wire around the stalk splitting the two groups. Using a hemostat or needle nose pliers twist the wire until you get a tight connection. Splice this into the ground wires and you have a simple yet fairly secure repair. The repair is not visible once the cover is replaced, there is a shield at the base of the stalk that hides the fix. Thanks Tom.

Tom Grahams guide to XJ S3 cruise control (7K ZIP/MSWord format)

XJS, Ignition, Timing Control System

Let me supply a bit of info on the XJS timing system. Of course we have the basics, at idle with no vacuum to the distributor timing should be 0 to 4 degrees advanced. At 2500 rpm with no vacuum to the distributor should be 18 degrees. With the vacuum hooked up to the distributor the timing should go off the scale at 2500 rpm. The system is set up so that a vacuum dump valve cuts off the distributor vacuum when the throttle is opened suddenly. This is accomplished by running ported vacuum to the dump valve. When the ported vacuum is applied the diaphragm in the dump valve is lifted and vents the distributor manifold vacuum to atmosphere. This creates a momentary dip in the timing to prevent initial on-throttle pinging. Part of the reason for this is because the fuel system will back off the A/F ratio to 22.5 to 1 at part throttle cruise. The momentary retarding of the timing gives the fuel system to readjust the mixture. On top of the dump valve system Jaguar decided to include a vacuum regulator that varies the amount of distributor vacuum advance depending on throttle position. There are over ten different settings for this regulator. I'll upload the chart from the training manual that I have so everyone can go test their regulators. With a 12.5 to 1 compression ratio in the H.E. motors they are very susceptible to pinging. If you can hear pinging damage is being done! A knock sensor to retard the timing would help the XJS as a safety feature. I've tried experimenting with the system by running vacuum straight to the distributor, sounded like a diesel when you hit the gas cruising down the freeway. I'm planning on setting up a small reserve fuel tank with 110 octane gas and a vacuum circuit to switch to direct vacuum. A couple of changeover valves to redirect the fuel and a couple of vacuum solenoids should do the trick. I really think the engineers have done a decent job on the XJS timing system. I don't know how much you can improve on it without making some major changes.

XJS, Ignition, Distributor Vacuum Regulator Specs

The distributor vacuum regulator is located under the right intake manifold near the rear. It is a brown cannister with three hose ports. Check distributor vacuum regulator as follows: Tee in two vacuum gauges to the distributor vacuum system, one to the manifold side and one to the distributor side. Run the engine with the climate control off and observe the vacuum gauges at the following rpm: Engine RPM Manifold Vacuum Distributor Advance (In. Hg) (In. Hg) 800 14.5 0.0 800 17.5 10.0 1200 17.5 10.0 1400 18.8 9.5 1600 19.0 9.8 1800 19.2 9.2 2000 19.4 9.2 2200 19.8 11.0 2400 20.0 13.4 2600 20.0 15.0 2800 20.5 17.0 3000 21.0 18.0 3200 21.0 20.0 3400 21.0 20.0 If the specifications are not met, replace the vacuum regulator and recheck the sequence. NOTE: During cranking for the first two seconds, the distributor vacuum will be 10 in. Hg. Also note that the Series 3 XJS uses a vacuum regulator that looks similar but has different specs.
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