Another XJ6 that won't start (this is an '86)

Battery is 12.68 volts and has a new charge
the engine act like it wants to start, but doesn’t. I had it running yesterday, it was hard starting but once it was running it was fine. headed down the driveway up the hill and it stalled. I checked spark, there was spark. I didn’t have my noids with me so I couldn’t test that.

I used a timing light to tell if there was spark or not. from the coil to the Distributor, yes and consistent. from the Dist. to the plug wires not consistent.

What’s the voltage across the coil? How to test the Electronic Ignition voltage.

What should the fuel pressure be at the rail?

Any tips on how to troubleshoot the EFI? All of the documentation suggests busting out the lucas epitest. this test tool is pretty much non existent.

Any tips on how to troubleshoot the electronic ignition too?

Here’s a diag tree for the CEI system.

The test assumes a fully charged battery

  1. Measure voltage at coil “+” terminal with key “on”. It should be within
    one volt of battery voltage. If not suspect a problem with the wiring to the
    ignition switch, or the switch itself.

  2. Measure voltage at the coil “-” terminal. Result should be the same as at
    the “+” terminal. If Ok, go to step 3. If not…
    Disconnect the wire from the amplifier from the “-” post of the coil and
    measure voltage again. Less than 2 volts means the coil is faulty. More than
    2 volts means the amplifier is faulty.

  3. Disconnect distributor pickup coil from the amplifier (this is the
    harness from the distributor that plugs into the amp). Measure resistance
    across the terminals. It should be 2.2k to 4.8k ohms. If Ok, go to step 4.
    If not, replace the pickup.

  4. Reconnect the pickup to the amplifier. Measure voltage at coil “-” post
    while cranking engine. The voltage should drop. If OK, go to step 5. If
    not, the amplifier is faulty.

  5. Check distributor cap and wires, distributor rotor arm, spark plugs, coil


Pull the distributor cap for a look-see at the innards and the distributor rotor

About 36 psi while cranking


1 Like

Thank you so much for your reply. I’ll give it a go. Also, thank you on the air pump information. It makes sense about heating the CAT up. it makes sense, I do notice how hot the exhaust is on the Series III over my Series I and Series II grandparents :man_shrugging:

I also found out that the Euro marketed cars didn’t have an air pumps had a simple relay that worked with the O2 sensor and the water rail sensor to turn on and off the cold start injector.

For what ever that’s worth,
Thank you again for your assitance

Adding to Doug’s sage advice, Mark - connect a test lamp between coil ‘-’ and ground…

With ign ‘on’, the lamp should be fully lit - indicating power through the coil, a back-up to voltage tests. While cranking, the lamp should dim and flicker - indicating, but not proving consistently, that the ign amp is working…

The ign amp works the same way as points - interrupting coil current to fire the coil. The EFI also uses the ign amp to trigger the ECU to open the injectors - a defective ign amp will not trigger the injectors. A physical test is to use a ‘stethoscope’ to listen to injector action - while cranking, the injectors should click regularly…

The standard triggering of the cold start injector is a thermotime switch at the front end of the water rail. It varies the time the injector is open according to coolant temps - your description does not fit the standard ‘European’ set-up. And in general The O2 sensor, when Lambda system is fitted, only influence the ECU…

As an aside; have your tried running on the other tank - the first step when the engine falter is to switch tanks. The second step is simultaneously to observe the tacho; if it drops to zero while the engine is still turning - it indicates that ignition has failed…

xj6 85 Sov Europe (UK/NZ)


Thank you Frank, I will give that a go, tonight after work. History on this car, it was a purchase off of craigslist for $400.00. the first time I fired it up the alternator churned out 14 volts, which cooked the radio. I immediately turned it off, replaced the alternator, that brings us up to date.

Thank you everyone for the help.

Does anybody actually own a Jaguar epitest?

14.4 Volts is what the amp should churn out?

European cars have just the thermo switch on the water rail. I’m not sure about the relay on mine…

There is a wire with a bullet connector that runs from the coil to the injector cable harness. With ignition on the injectors should click every second time you connect the bullet connector so you don’t need to crank. (This is Frank’s EFI trigger). Don’t flood the engine do it once per injector or twice.

There is a contact in the AFM that stops the fuel pump as soon as the flap closes, I doubt it is defective but you might open the cap and have a look.

But your Distributor seems to be the bad boy so fwiw good luck. At least you’re home. As there is good spark from the coil the amp should be fine, and the pickup too?

From afar. Yup, good work in using the strobe to check spark at the HT wires.

As already mentioned, pull the distributor cap and check the underside As well as the rotor.

Plus, each wore tower atop the cap. Internal corrosion in them

Don’t forget poor HT wires. High resistance a cause of a miss. but, just might be so bad as to fail to deliver enough spark in the chamber to run.



with everything said so far well taken as perfect advice, looking at the fact that your perfectly running car is reported to have stalled when going “up the hill” might rather suggest a fuel problem as per Frank’s advice. Or were you rather going “down the driveway”?

Bottom line I wouldn’t exclude the fuel side from the suspects.

Good luck


75 XJ6L 4.2 auto (UK spec)

Status update
Battry started out at 12.68 V and steadly dropped during testing down to 12.18
Coil + got less than 1/2 volt less than the battery at 11.96
Coil - Same as plus
Disconnected the Amplifier measured the resistence across both terminals and got a nothing. Open Circuit. Cleaned the contacts on the pick up for the amplifier with spray contact cleaner tried again Still nothing. While trying to figure out to do next, I sprayed the contact cleaner on the coil posts, temp sensor on the water rail.

pulled a injector plug and stuck the NOID on the #1 injector. cranked it over just to see if the injector light would com on, I wasn’t suspecting it to but what the hell.
at first nothing on the timing light or the NOID. then all of a sudden it fired up ran like shit initially cleared up, then the idle smoothed right out.

Let it idle for a bit. Noticed the temp and gas, gauge didn’t move and were buried pointing to the left. Oil pressure popped up to 40psi, and didn’t move an inch. volts were just pass 13.3
Timing is what looks like 4 BTC at 1,000 RPM I think that’s supposed to be 8 BTC at 750 rpm. this would account for the hard start.

I’ll fire it up in the morning and see if I get more of the same shit - won’t start. I’m a bit leery to take it down the road again for fear I’ll get down the drive way at the bottom of the hill and have it quit.

Why it started running all of a sudden? Couldn’t tell you.

Oh, and I was about to test the fuel pressure to the rail just before it fired up.

The spark is still iritic which is a bit worrisome; come to think about it i had the same issue with the Green Series III when I first got it, and I swapped out the coil, and everything work like a champ. Oh, the coil was a MSD performance coil with an internal ballast. The damn thing had some gravity to it, and it was also thicker, so i had to make a new bracket to hold it in place.

I’ll fire it up in the morning and keep you posted on my progress

You all may need to know that after checking to see fuel pressure is present , ( simple by loosening a hose or listening to the pump ) best to loosen a line due to eliminate a filter or blocked line ,just prepaid for small amount of fuel being sprayed… if spark is at the plugs , very simple to check by removing a plug and allowing it to be grounded look for spark if so dont listen to everything you hear about checking ECM as a expenceplast and almost not the problem .is way wrong and should be among the first things to check . I had to learn this the hard and expensive way , I’m no mechanic but from my experience with a series 3 xj6 are if it starts hard and want to run like shit , most likely has spark and fuel so if you wanna beat around the bush and check every little possibility you may end up finding things needs attention and improving the odds of making your jag more dependable , but your problem your after is in the ECM , everyone makes these cars seem difficult to diagnose and make run and the truth is they operate on a GM module from a GM HEI distributor , and most all know they fail mostly due to heat so why does Jaguar mount it flush to the head of the engine . I supposed because there is no hotter place. To Mount it ??? So after conducting the simplest of tests required on any gas driven engine to determine gas and spark go straight to that ECM every things tell you not to suspect and fix your jag so it can be one of the most dependable cars you ever owned ,

1 Like

Firstly; refer to #3 on Doug’s list, Mark. You measure the pick-up resistance on the connector on the wires going ‘from’ the amp ‘to’ the pick-up. Which should indeed read 2,2 - 4,8 Kohm - confirming pick up coil integrity. Measuring resistance on the ‘in’ connection (from the coil) is sort of meaningless - the amp is electronic…

You likely have an intermittent fault - and it must be caught on the hop. That there were initially no response from the noid, but when it lit up it started - or vice versa. Which implies no amplifier action initially - which may be caused the pick-up or the amp itself.

With an intermittent; repeated testing is required for consistency. Connect the noid between the coil neg and ground; if the noid is lit with ign ‘on’ and flickers while cranking and the engine starts - it is normal. If ‘no start’ coincides with no noid flicker - the resistance in the pick up should immediately be checked…If resistance is to spec each and every time, but noid flicker comes and goes - it may be that the pick-up is adrift. This should be checked together with pick-up air gap (0,008 - 0,014")

In addition; if the ‘coil noid’ is dark in ign ‘on’, or stays/goes dark in ‘crank’ - coil power is lost, or there is a break in the coil.

You may also use two noids, one at the coil as described and one on an injector. And combine the repeated tests with spark testing - using a spare, triple gapped, spark plug connected to the plug lead of same cylinder as the injector noid. Thus supervise both ign and injection at the same time - ign and injection both use the ign amp/pick-up, but are otherwise two entirely separate functions…

It’s complicated to describe, but the testing itself is straight forward - and will not interfere with engine starting if the fault is ‘absent’.

In short, normal is with ign ‘on’; coil noid fully lit, injector noid dark, no plug spark. Cranking; coil noid dim and flicker, injector noid flicker - and strong blue spark on the spark plug. Repeat as required to ensure consistency…:slight_smile:

If any of this fails coinciding with a ‘no start’ - the problem is in the affected area, ign and/or injection. If the ‘no start’ is independent of either; you may have an iffy ign amp (ign amp testing is not 100% certain) - or the fault is elsewhere…

xj6 85 Sov Europe (UK/NZ)

iritic? Or eratic ? Sorry, I do that as well, a lot!

But, that would be my focus. Ignition!!! And, add in the odd instrument behavior. to me, from a past adventure, the ignition switch itself. The white wire fro that switch does a lot if things, powering instruments and the ignition coil. A NOS switch via David Boger fixed a lot of stuff in my car.

Rough and ready process. Jump 12v from battery to coil +. Crank it up. I have an idea it will run nicely.

The minor timing deviation is not an issue as to running.

Indeed, the GM amplifier is like all electronic stuff heat sensitive. But, others have pointe out, it is not on the head, but on the water rail, a lot different

On my a lot different engine, but similar ignition module, it is mounted on the cast iron head. But, with a heat sink and heat transfer enabling goop.


Another status update
Yesterday the Series III XJ6 fired up, I let it idle for a spell, then backed down the driveway and headed for the top of the hill. got to the top, All is good, then around the horse shoe. As I got about half way around the horse shoe heading for the hill to my house, The engine started cutting out, like it was out of spark or gas.

I’ve got spark - timing light assisted
I’ve got 36 psi of fuel pressure at the rail
I didn’t check the injector with NOIDs today but they were working… I’ll check that tomorrow.
Cap and rotor cleaned up and were fine, clean up the spark plugs; which had all of the indications of running rich.

So if the engine quits when it gets up to temp, then that could be either a coil, or an amplifier right? and the amplifier provides the signal to the ECU to fire off the appropriate injector - right?

I will review this tomorrow too.

thank you all for your help

Vital reaction, Mark - engine misfiring; instantly change to the other tank and ogle at the tacho. If the engine then recovers; it is not getting gas from that tank - which can have various causes. If the tacho drops to zero while the engine is still turning - you have lost ignition…

These are standard ‘on road’ reaction - providing a quick-test of two vital areas; fuel and ignition…

However if no clue appeared; the coil, and especially the ign amp might indeed be heat ‘tender’. I strongly advice using a spare spark plug, triple gapped, to test ignition is the best simulation of what happens to the spark inside the cylinder…

In principle; ignition requires a fully functioning ign amp - an iffy amp may still provide injector operation while there is no ignition.

But it is very important that the ign and injection testing are performed quickly, while the fault is presumably still present. Neither tests will interfere with starting - so if the engine actually starts during testing the tests should show ‘normal’…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Also, did you check all connections; and when you let the car idle so it gets hot would the overheat condition show?

Current Status.

  • hasn’t run since the trip around the neighborhood
  • I checked fuel pressure, and it’s 36ish psi at the fuel rail
  • Using my timing light, I do have spark at

What’s left to check.

  • Plug a noid into the injector to see if it’s getting a signal
  • Check the condition of the ECU plug and connections
  • Possible go over Doug’s list again to see if anything’s changed.

No, the engine barely gets up to temperature.

You mentioned the gauge doesn’t work but after ten minutes idling (in gear can help) is must be warm enough to duplicate the short drive, heat wise…
But if it doesn’t run anyway that’s not having a point either, so you can try if you can make the injectors click by repeatedly connecting the aforementioned bullet connecor from the coil to ecu. If they click it should start, right? And if no start but clicking that might not be the issue, at least not in that particular moment… it’ll sort out.


How, Mark…?

xj6 85 Sov Europe (UK/NZ)

I put the induction lead over the HT lead, if it lights, i have spark.

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