Hello all
Some may recall that I have been working on a friend's 1988 XJ6 to revive it after a long term storage.
I had actually finished the car except for some sheet metal work on the floor of the trunk.
I returned the car with the instructions to drive it around for a couple of weeks and then I would work on the repair of the trunk floor.
Unfortunately the car survived less than a day before I got a call that it died and wouldn't restart.
The car was towed back to my shop where I have spent a LOT of time this week trying to diagnose the root cause of the no start issue.

Basically the car has no spark. The starter works and spins the engine over just fine. The battery is new and fully charged.
I am checking for spark by unplugging the coil wire from the center of the distributor cap and holding the end near a ground point on the engine.
I have done lots of things to try and figure out why it won't start but so far I have been completely unsuccessful at trying to solve the issue.

The car acts like the crank sensor is bad but I have done lots of things to check that and I will detail all of the steps I have gone through so far.

I have tried swapping in two other crank sensors, checking the resistance readings from the crank sensor at the actual electrical connector at the front of the motor and at the pins on the engine management ECU plug.
I have checked at the electrical plug for the engine management ECU for the appropriate AC voltage signal when cranking the engine. I do get AC voltage at the appropriate ECU pins corresponding to the wires coming from the crank sensor.
All of this looks good. But still no spark at the plug and zero movement of the tachometer when cranking the engine.
Although I have no spark from the coil wire, I also checked the ignition rotor to see if it had electrical conductivity and it was fine.
I have power at the coil (checked with a test lamp on both the positive and negative side of the coil) with the ignition switch turned on.
I also have power at two of the wiring harness pins going to the ignition module that sits behind and under the coil.
Earlier this evening I also put a noid lamp on one of the injector plugs and got nothing when cranking the engine. No blinks of the noid lamp when plugged into the harness in place of an injector.

I am fortunate that I also have another car in the shop with the identical engine management system that runs fine. So today I tried swapping some parts so I could confirm working parts or not.
I have swapped the actual engine management ECU from the no start car to the running car and the running car starts and runs fine with the no start ECU. Put the no start ECU back on the no start car and it still would not start.
I also swapped the original crank sensor from the no start car to the running car and the running car starts and runs fine with the no start crank sensor.
Earlier in the week I removed the ignition control module from the the running car and temporarily plugged it into the no start car but that made zero difference. The no start car still would not start with the running car's ignition control module.
I also took this same "good" ignition control module and put it BACK on the the the running car and it still runs fine with it's original ignition control module.
I have checked the action of the fuel pump when the ignition switch is first turned on and I can hear the pump do it's initial pulse so that tells me that the main and fuel pump relays are working as expected.
I also checked these relays using a test lamp and the ignition relay, the main relay, and the fuel pump relay all have power on pin 30 and pin 87 when I turn the ignition switch to the on position.
I also swapped other identical relays in for the main, ignition and fuel pump relays but that had no effect.

I am running out of things to check so I really hope someone here might have some suggestions.

PLEASE HELP!

 

Hi Steve,

Have you tried swapping the coil and/or ignition amplifier module? The tachometer signal passes from the ECM to the Instrument Cluster by way of the ignition amplifier and through one terminal of the coil.

Have you tried swapping the king lead (coil-to-distributor) from the running car to the no-start car?

Have you measured the voltage at the ECM while cranking? If the voltage sags below something like 10.4 volts, the ECM will not trigger the ignition to fire. Even with a healthy, fully-charged battery, the voltage at the ECM can be low due to looseness or corrosion of various battery power and ground connections.

Cheers,

Don

 

Hi Don:
Yes, I said that I tried swapping the ignition control module from the running car to the no start car. It made no difference.
I also tried a different coil on the no start car and today I did try another coil wire.
Previously I had checked the existing coil wire as well with an OHM meter to make sure it was good.
The ignition wires look to be nearly new however.

I will check the voltage to the ECU while cranking tomorrow.

 

Hi Steve,

It might be worth swapping the coil also, and inspect the old coil for deterioration of the plastic around the electrical terminals.

Also, in case you aren't aware, the metal plate to which the ignition amplifier module mounts is a heat sink, and I seem to recall that a thin layer of thermal compound should be applied to the module before it is installed to the heat sink plate. You don't want to run the module for long without being mounted on the heat sink due to the risk of overheating.

I remember that at some point Jaguar repositioned the amplifier because it was found that its orientation on the early cars was leading to problems. I'll see if I can find the TSB.

Here it is:

18 - 41 Intermittent Power Loss - Tach Drops to Zero - Reposition Ignition Amplifier - Service S 439

Cheers,

Don

 

Today I checked the voltage at a few different terminals on the ECU with the key in the on position.
Using a digital VOM I got 12.10 volts between terminals L13-1 and L13-18, 12.09 volts between terminals L12-10 and L12-17, and 12.20 volts between terminals L12-14 and L12-17

I didn't have a helper available to turn the ignition key to the start position so I could recheck these voltage readings with the key in the start position.
I hope to be able to do that tomorrow.

I also need to put the battery on charge again since I have not done that for about 4 or 5 days.

Yes, Don, I am aware that there is supposed to be dielectric grease between the bottom of the ignition module and the aluminum heat sink.

 

Hi Steve,

It's not dielectric grease you want, which is just a silicone insulating grease. You need thermal paste, which is silicone based but contains zinc oxide to improve thermal conductivity.

Cheers,

Don

 

Yesterday I removed the ignition control module from the no start car and installed it onto the running car and the running car would not start with the module from the no start car. I swapped between the two modules three or four times on the running car just to confirm this result. Recall that I said the crank sensor AND the ECU from the no start car both worked fine on the running car.

So at this point I was REALLY positive I had found the root cause of the issue however when I took the ignition control module from the running car and did a complete (bolted it all down with coil in place and proper ground connections on the aluminum heat sink) onto the no start car IT STILL WOULD NOT START!!! ARGH!!!

So at that point I started measuring voltages at the pins on the ECU harness again while a friend turned the engine over by turning the key to the start position. I did detect some voltage drop when doing this compared to the reading I got when the ignition key was in the run position.

 

I finally got it to start today. It seems that not only did it have the defective ignition control module (some people also call it an ignition amplifier) but it seems the barrel connector where the crank sensor plugs into the wiring harness is “temperamental”.

Today after charging the battery all night, and cleaning the various wiring harness ground points, I got it to start ONCE. Then the next time I tried it, it wouldn’t start again so I swapped out the crank sensor AGAIN and it started a second time. Then later it wouldn’t start. This time all I did was unplugged and replug the barrel connector for the crank sensor and then it was reliably starting again.

After I got it to reliably start again, I swapped the original ignition module back into the car (carefully without touching the crank sensor wiring in any way) and it immediately stopped starting. Swapped the OTHER ignition module back into the car and it started again. So at this point I can definitely say the original ignition module is kaput.

 

I hope you don't have any dielectric grease in that connector because that will give you all sorts of trouble. Dielectric grease is an insulator and will prevent good connections. Use it on OUTSIDE of connectors only, never on pins or inside connectors etc.

Just checking!

Laarry

 

No grease inside the connector. Totally dry