My 1997 XK8 (95k mileage) recently exhibited the "engine fault" and "poor performance" messages which, based on my research on this forum, typically result from ecu failure. I removed the ecu and saw that it had been repaired by a previous owner 10 years ago, when I assume they replaced the original capacitors. I opened the ecu and saw that the large capacitor on the lower left hand portion of the board (upper right in the pic) had failed and, assuming that the capacitor just needed replacement, I sent it out for repair. The repair shop said that the capacitor had shorted as a result of some other problem in the car and that the failure had caused significant damage to the circuit board. They said they could attempt a repair but wouldn't be able to warranty the repair. I decided to purchase a used ecu instead of throwing more $$ at the damaged one.

I have since purchased another 97 ecu but before installing it, I would like to try to see if I can find any problem that may have caused the capacitor to fail. My planned steps would be to 1) check all fuses for evidence of a circuit issue, 2) verify that the ecu fan is working properly, and 3) check all of the ground connections on the car.

My questions to the wizards on the forum:
1) Has anyone had a similar ecu failure, and if so were you able to determine an external cause?
2) Does anyone have any additional advice on how to find the source of the problem?

Thanks in advance

 

Checking if the ECU fan is good is something I have not done. Can you see it or hear it ? whats the best check method?

UPDATE
I put my ear to the ECU box and I could hear it running ..

 

Most likely no cause other than the capacitors themselves, and it is common on the '97 ECM. They are well beyond expected lifespan at 25+ years. Some die in their sleep, some ooze out the internal electrolyte, some emit magic smoke, and some just get extremely hot.

You are lucky to find a replacement ECM as they are rare (only fitted to MY97 XK8, and no crossover from the X308). I hope it didn't cost you a body part!

It would be a good move to replace the ones in the replacement ECM as they may be original. There are seven, and it's an easy job for someone competent with a soldering iron.

I made a list of the parts needed here:
https://www.jaguarforums.com/forum/x...6/#post1806456

 

All these caps seem to be available from Mouser electronics at sensible prices /...the whole lot will come to about £15 I just put the cap numbers in google and it came up.
It also gives the size if you want to buy else where.

Interesting the life is quoted as 5000 hours which at 30 mph (average vehicle speed ) is 150,000 miles...5x the life of a headlamp bulb !

 

Thanks for the input and capacitor part number references... very helpful and much appreciated. I haven't yet received the replacement ecu (found a used one on Ebay for $150... seller says it works... hope he's right) and I'll definitely look at the caps before I try it. The ecu repair shop is shipping the old one back, and I may try to source a local repair on that one if I can find a friend whose good with an iron that's willing to give it a try. Just in a holding pattern at the moment. I did check all the fuses today, and also determined that the ecu fan is working (put 12v to the connector in the ecu box). Plan to check ground connections later when I can get it on the lift.

And I'll probably keep looking for another spare, just in case.... Will update when (or if) things progress...

 

If you decide to retire your old ECU, I would be interested in examining it. I do not know what “extensive damage” means, but I would be interested in trying the repair myself and testing in my ‘97 XK8 to see if I can manage it.

That is, assuming you are done with it…

As for the fan, I wondered the same thing. I am curious to see if it comes on with key-on without the ECU attached

 

Key on and the fan runs I can hear it if I put my ear to the ecu box.

SOLDERING PERSON
If you can spot any radio ham antennas in your area they are always good at soldering and am sure would do it for free.
G6EIF

 

There were many manufacturers that were bit by the bad cap problem, HP being one. Seems a secondary manufacturer started selling capacitors with a flawed electrolyte that turned caustic enough over time to compromise the case. It isn't unusual for 20 year old electrolytics to fail anyway. Often refurbishers of old radio and stereo gear replace them. They lose value if nothing else.

 

I'd definitely give that a go. As 'they' say, they aren't making any more and already scarce. There's not a lot circuit-wise going on in that corner of the module so it is a possibility.

Greenforest56 had a very similar issue, only his was slightly worse:
https://www.jaguarforums.com/forum/x...4/#post1779699

@pistnbroke - are you active on air at all?
GJ4TBW

 

Michael,

That's the plan. I know a couple of guys that I used to work with who are pretty good electronic techs. Just need to see if I can talk one of them into tackling it.
Thanks for the reference to that thread, I hadn't seen that one yet. Looks pretty similar.
I'm starting to wonder if an issue with the throttle motor circuit may be affecting that corner of the board...

 

For Michaelh
Did research on the capacitors you listed ...some are only rated at 2000 Hrs admittedly at 105 deg C so I would conclude that the fan running is essential or its failure causes failure of the caps.
If the air being used for cooling comes from the passenger compartment I would think that does not go over 30 deg C ....Keep the aircon ON !!

 

I did consider this, and no doubt a failed fan wouldn't help, although it does appear to be predominantly a 97 thing...

Had a quick look on Mouser's site at alternatives, but the choices thin out a lot the higher spec you go. Military-grade would be nice!

I didn't make a note of the part #s I pulled, but I may still have them somewhere. I'll check when I get a mo.

Cheers,

 

According to the diagram it's a simple on with ignition, no other input.

 

If you look at the photos of the damaged ECU you can see a diode to protect against battery reversal so the big 560uf cap can go from the anode side of that (+) to earth rather than be on the board. Jumper wires to repair the continuity below

 

Just a quick update... the used ecu, although a KJA1410AN, rather than the original KJA1410AK, seems to be working. All fuses are good and the ecu fan works. Still want to check all ground connections sometime soon and also talk to my buddies to see if one of them will attempt a repair on the old ecu.... Thanks to all for the great input, particularly the capacitor numbers!
Grady

 

Very glad to hear it! Hopefully one of your friends is interested. If not, LMK if you'd be interested in selling me the damaged one; I enjoy a challenge & would love to have a refurbished ECU on the spare shelf I already re-capped mine, so I don't have a real need, but I am comfortable with an iron and I've been inside these units before.

 

Ok, will do, thx

 

It would be nice if someone would offer a drop in replacement for our ECU's.

 

Its not the solid state electronics that fails but the capacitors . I bought a TV in 2000 . In 2010 it failed due to capacitors leaking in the power supply , did it again in 2020.
So with the cars having passed there use by date treat it as a maintenance item.

ECU Repair.pdf - Google Drive