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my first post here because I am completely lost. Bought a 1997 Jaguar XK8 and it soon started to show issues.
These are the errors I got: P0352 Ignition Coil B Primary/secondary Circuit Malfunction P0353 Ignition Coil C Primary/secondary Circuit Malfunction P0355 Ignition Coil E Primary/secondary Circuit Malfunction P0358 Ignition Coil H Primary/secondary Circuit Malfunction P1368 Ignition System Failure Group 2 Pending
I researched a lot and seems that it‘s a typical issue wirh early Jaguar XK8 ECU. So I sent it to a shop and they replaced all the capacitors. But the Problem is still there.
What else have I done? I changed all the igintion coils from the affected cylinders with the non effected ones. Changed the igintion modules left to right. Got new spark plugs.
I did a compression test. Got 130-135 psi on all cylinders. Not that great but the engine was cold and as far as I know it‘s more important that the cylinders are close together.
So how does the error come up: It appears after a bit of driving. Like after 20km ~. And most of the time it starts when I am cruising, low rpm and slight to no throttle. Sometimes when I give it immediately more throttle it goes away instantly. But one it startet it‘s coming back. And it then stays. I can clear all codes while driving. Sometimes it‘s fine for a few seconds sometimes it‘s gone.
And sometimes if I keep ignoring it it goes away completely and I can drive it for hours and it‘s not coming back.
I looked into the ECU after the repair and found one capacitator should have 50V 560uf according to my research and the put in a 35V 560uf. Could it be a wrong capacitor? Maybe it was previously repaired with a wrong capacitor and they simply replaced it with the same one. And I found one not so nice spot between the capacitors.
Anyway I am lost. Don‘t really know what else to do and look for. Will test the wiring for a short circuit. So if anyone has more ideas that would be great!
I looked into the ECU after the repair and found one capacitator should have 50V 560uf according to my research and the put in a 35V 560uf. Could it be a wrong capacitor?
Unlikely to matter as it's basically a 12V (up to about 15V) system.
Those cylinder errors on 2 banks indicate a fault with ignition control module 2, the ICMs are located on the firewall behind the throttle body. There are 2 but I'm not sure which is which, you will need to trace the harness to determine that unless anyone on the forum knows.
Each ICM manages 2 cylinders on each bank (not all 4 cylinders on 1 bank), ignition control module 2 manages the 4 cyclinders you are getting errors for, it might just need contact cleaning or maybe it's breaking down under heat cycling. You could swap ICM 1 and 2, if the problem moves to the other 4 cyclinders - you have nailed it.
Those cylinder errors on 2 banks indicate a fault with ignition control module 2, the ICMs are located on the firewall behind the throttle body. There are 2 but I'm not sure which is which, you will need to trace the harness to determine that unless anyone on the forum knows.
Each ICM manages 2 cylinders on each bank (not all 4 cylinders on 1 bank), ignition control module 2 manages the 4 cyclinders you are getting errors for, it might just need contact cleaning or maybe it's breaking down under heat cycling. You could swap ICM 1 and 2, if the problem moves to the other 4 cyclinders - you have nailed it.
I already swapped them. Still have the same cylinders that through error codes. So it doesn‘t move.
and I also checked the ECU fan. Connected a small 12V battery to it.
But maybe the ECU is getting to hot. Maybe that‘s why it‘s only showing the error after some time of driving.
I'm thinking not ECU, if it were then I would expect the fault to be on all cylinders, I would not expect the problem to be explicitly manifested on only the ICM 2 circuit. Open to being wrong here
So......if you swapped the ICMs and the fault didn't move and you have already swapped the coils with the same results then the harness warrants investigation:
Feeds to ICM 2
Feeds from ICM 2 to the ignition coils
Since all ICM 2 cylinders are faulting and it doesn't appear to be the ICM itself I would look for something common to the ICM, a ground wire perhaps or bad input ICM pin / socket - the likelihood of those 4 specific cylinders wiring failing simultaneously is low.
Stupid question but how do I go about cheing the harness? Check if I get connection with ground on one of the pins?
I don‘t really see why it would be the harness if the error only shows after some time of driving.
But will def check it!
do a visual check of the coil harness - based on the age of the car and amount of engine heat it has sustained over the years, I would bet the insulation on the wiring harness is flaking off so that there is intermittent contact among the leads. If it is the harness, short term fix is wrap each lead with electrical tape until you can source a harness
I looked into the ECU after the repair and found one capacitator should have 50V 560uf according to my research and the put in a 35V 560uf. Could it be a wrong capacitor? Maybe it was previously repaired with a wrong capacitor and they simply replaced it with the same one. And I found one not so nice spot between the capacitors.
That is the wrong capacitor, although it is unlikely to be the cause of your current problem, the capacitor is more likely to fail at some point because it is underrated. Although it's a 12v system, higher rated capacitors are specified when the circuit is subject to voltage spikes (like you get from things like ignition coils), so really it should have been replaced with a 50v version. There is a list somewhere on the forum of all the capacitor values along with part numbers - it's important really to match them as close as you can. If it was me, I would get that capacitor changed, especially as something isn't right with that system.
By the way, the caps also have a temperature rating - you might want to check the new ones are correct.
Do not like the look of some of those tracks/traces shown in you photos. They could do with cleaning and continuity/conductance tests. It is possible that if they have been weakened by the capacitor leakage they could go high resistance or even open circuit with temperature changes.
That is the wrong capacitor, although it is unlikely to be the cause of your current problem, the capacitor is more likely to fail at some point because it is underrated. Although it's a 12v system, higher rated capacitors are specified when the circuit is subject to voltage spikes (like you get from things like ignition coils), so really it should have been replaced with a 50v version. There is a list somewhere on the forum of all the capacitor values along with part numbers - it's important really to match them as close as you can. If it was me, I would get that capacitor changed, especially as something isn't right with that system.
By the way, the caps also have a temperature rating - you might want to check the new ones are correct.
I have found that thread. Seems everything else is in spec except the volt rating.
I will get it changed for the correct voltage.
Do not like the look of some of those tracks/traces shown in you photos. They could do with cleaning and continuity/conductance tests. It is possible that if they have been weakened by the capacitor leakage they could go high resistance or even open circuit with temperature changes.
My. est guess right now is that it‘s got something to do with temperature. Because the issue appears after driving it for a while or in slow traffic.
I removed the cover holding the ecu for more airflow. So will test if that helps. But that‘s just a guess
A few decades ago when I worked at the dealer, we had a car (X308 sedan) out of factory warranty but in Jaguar certified used car warranty that would stop running after a while in traffic or slow driving.
NO DTCs so we looked at the history and saw that Jaguar bought it back in warranty and sold it again as a used car with warranty.
Another Jaguar dealer could never duplicate the fault so we called a Field Service Engineer to assist.
I took him out driving and the car did not run poorly or stall.
We came back to the shop and he wanted to look at the ECM.
We could not touch the ECM case with our bare hands. It was so hot and he stated that that was NOT NORMAL.
He authorized a new ECM so it was ordered and replaced/configured to the car.
I never saw that car again so I guess we fixed it?
Last edited by motorcarman; Jul 27, 2025 at 08:30 AM.
You've eliminated a lot by swopping all the coils and plugs across the two banks, and switching the ignition control modules.
You could check for spark on the affected cylinders, but I doubt if an intermittent would take out a cylinder group (all 8 cylinders share a common ground and B+ connection). You're then left with whatever is part of the common path:
(i) the ICM, which you've already eliminated by substitution.
(ii) the wiring between the ICM and the ECM
(iii) the ECM itself.
As per RJ237, I would still be suspicious of the ECM - particularly since the issue is heat-related and, as noted, the circuit board really should be cleaned up properly and checked for open circuit / leaky tracks.
Whoever did the job has used a variety of different parts; I can see three different manufacturers, but not the temperature rating, which should be 105° C.
There is also one cap under the daughter board (four screws on the top). It's worth checking in case it's been missed.
Replace them all with good quality parts, e.g. Nichicon as they were the OEM. You may have seen the horror pictures where that 560μF has failed badly and burned the circuit board
Ignition system failure
