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Well I was enjoying my rejuvenated transmission and drove the car to work. Decided to move parking spots, and 40 mins later dead, cranks but no start. Figured it’s flooded so left the car overnight. Still no start, wonky OBDII won’t read, so instrument cluster weirdness AGAIN. Really don’t want to pull my plugs at work where vehicle maintenance is prohibited. Frustrating. Checked the simple fuses etc. waiting for the parking spot next to the jaguar to open up so I can throw jumper cables on it. 140,000 mile Jaguars are a recipe for sadness.
So I finally resigned myself to staring at wiring diagram, the neutral safety switch would cause a no crank, not a crank with fuel and ignition cut out, so I pulled the ECU and opened it up. At first I thought it looked great, so while staring at it I noticed this...
that little blob of green is on the start OK input, so I cleaned it a little....
that missing trace is the canbus, one leg of it anyway, so that explains the TCM to ECU canbus DTC I had. The trace for the start OK was still intact so I was puzzled, but I was going to change some caps while I was in there. I couldn’t find my box of caps, so I had to fight traffic to the only supply house left in town, got back with all but the main filter cap. So, the cap leakage dissolved the trace, it also dissolved the solder pad, and most of the Via, so I hope it was a single layer board, but it’s not, so I the decided to cut the others out to preserve the Via and pads involved.
The IMPORTANT thing to know here, is that if you cannot solder at this level, OR remove components at this level pay a professional to do it. These caps all pass through at least 3 levels of traces I could see, if you destroy an inner trace you will be screwed. So results?
Every cap was leaking to some extent, half of them were corroding at least one leg, and one joint, so big problems were on the way.
reinstalled the ECU and still had the same issue! Aaaarrrrgggghhhh. Cleared the DTC and it would keep reoccurring , without trying to start, which is what sets the code. So frustrated I just tried to start in every gear position sequentially, PRND432....234DNR, of course it only cranked in P and N as it should , and properly interlocked in all other positions.......then when I got back to park and the ‘engine fault’ message did not reappear. So I started the car, then got it out of the parking garage so it could be flatbed towed if I needed. Drove it 26 miles in 5 o click traffic and it didn’t skip a beat, 5-4 kick down was way smoother, I guess because CANBUS was working again. Who knows, maybe BCM sends a signal? It resolved for now.
lesson? Your 1997 ECM is going to die a horrible death if you leave the original capacitors in it.
I’d thought bore wash, but now I see ‘engine fault’, brought my vcm and IDS to work and pulled 1517, which I believe is transmission switch, so I may be inhibited at this point. I’d disassembled and cleaned the position switch prior and thought I’d solved it. All my indicators seem to work properly when I shift through them. I have an instrument cluster issue also aggravating the process.
So I finally resigned myself to staring at wiring diagram, the neutral safety switch would cause a no crank, not a crank with fuel and ignition cut out, so I pulled the ECU and opened it up. At first I thought it looked great, so while staring at it I noticed this...
that little blob of green is on the start OK input, so I cleaned it a little....
that missing trace is the canbus, one leg of it anyway, so that explains the TCM to ECU canbus DTC I had. The trace for the start OK was still intact so I was puzzled, but I was going to change some caps while I was in there. I couldn’t find my box of caps, so I had to fight traffic to the only supply house left in town, got back with all but the main filter cap. So, the cap leakage dissolved the trace, it also dissolved the solder pad, and most of the Via, so I hope it was a single layer board, but it’s not, so I the decided to cut the others out to preserve the Via and pads involved.
The IMPORTANT thing to know here, is that if you cannot solder at this level, OR remove components at this level pay a professional to do it. These caps all pass through at least 3 levels of traces I could see, if you destroy an inner trace you will be screwed. So results?
Every cap was leaking to some extent, half of them were corroding at least one leg, and one joint, so big problems were on the way.
reinstalled the ECU and still had the same issue! Aaaarrrrgggghhhh. Cleared the DTC and it would keep reoccurring , without trying to start, which is what sets the code. So frustrated I just tried to start in every gear position sequentially, PRND432....234DNR, of course it only cranked in P and N as it should , and properly interlocked in all other positions.......then when I got back to park and the ‘engine fault’ message did not reappear. So I started the car, then got it out of the parking garage so it could be flatbed towed if I needed. Drove it 26 miles in 5 o click traffic and it didn’t skip a beat, 5-4 kick down was way smoother, I guess because CANBUS was working again. Who knows, maybe BCM sends a signal? It resolved for now.
lesson? Your 1997 ECM is going to die a horrible death if you leave the original capacitors in it.
Drive around a bunch today and got a repeat, basically this:
if the car cranks fir more than 3 seconds without starting I get an ‘engine fault’ message, If I flood clear the pedal and back off it just starts.
if I keep cycling the ignition I just get locked into a start inhibit mode, with the code.
So I’ve got some sort of hot start flooding issue underlying all this weirdness.
Last edited by Stephjac; Apr 30, 2021 at 12:04 AM.
well done!...... its not every owner who has the courage to delve into the electrical workshop schematics lol
Excellent detailed post and very helpful for others with similar ECU issues.
Hope you find a lasting solution
Well beyond my knowledge of the boards but hats off to those that can.
Yes, I can see a bad line or a leaky capacitor, that's my extent or handing it to someone who can to replace the parts.
Thanks for furthering my knowledge.
Drive around a bunch today and got a repeat, basically this:
if the car cranks fir more than 3 seconds without starting I get an ‘engine fault’ message, If I flood clear the pedal and back off it just starts.
if I keep cycling the ignition I just get locked into a start inhibit mode, with the code.
So I’ve got some sort of hot start flooding issue underlying all this weirdness.
So the ECU wasn't the issue? I must admit I couldn't see much wrong with the PCB, all the copper looks intact, just the green lacquer missing in places. Or am I missing something? Strange for all those capacitors of different values all to start leaking in such a short time don't you think?
Last edited by kansanbrit; May 3, 2021 at 08:22 AM.
So the ECU wasn't the issue? I must admit I couldn't see much wrong with the PCB, all the copper looks intact, just the green lacquer missing in places. Or am I missing something? Strange for all those capacitors of different values all to start leaking in such a short time don't you think?
the compounding issue is the neutral safety switch, usually it won’t crank if it’s screwy, but in 1997 the micro switches go to the BCM and the rotary switch feeds the ECM and TCM, so my rotary switch is wonky, so the car cranks but no start from ECM. I had a CAN bus failure ECM to TCM, and an SCP/j1850 communications failure in the instrument cluster which may affect the BCM to ECM. I’ve verified the rotary switch issue.
SO it appears I’ve been chasing to separate issues compounded.
So the ECU wasn't the issue? I must admit I couldn't see much wrong with the PCB, all the copper looks intact, just the green lacquer missing in places. Or am I missing something? Strange for all those capacitors of different values all to start leaking in such a short time don't you think?
Well, the caps are 24 years older and exposed to wild temperatures, but I am perplexed by the corrosive nature of the electrolytic discharge. I’ve never seen that on any other application and I’ve routinely replaced electrolytic caps for years, including nichicon, which are high quality capacitors. The network issues really impeded my ability to scan the system.
the compounding issue is the neutral safety switch, usually it won’t crank if it’s screwy, but in 1997 the micro switches go to the BCM and the rotary switch feeds the ECM and TCM, so my rotary switch is wonky, so the car cranks but no start from ECM. I had a CAN bus failure ECM to TCM, and an SCP/j1850 communications failure in the instrument cluster which may affect the BCM to ECM. I’ve verified the rotary switch issue.
SO it appears I’ve been chasing to separate issues compounded.
Which switch are you calling the rotary switch? Transmission or ignition?
Well, the caps are 24 years older and exposed to wild temperatures, but I am perplexed by the corrosive nature of the electrolytic discharge. I’ve never seen that on any other application and I’ve routinely replaced electrolytic caps for years, including nichicon, which are high quality capacitors. The network issues really impeded my ability to scan the system.
Why are they exposed to 'wild' temps? And what exactly did the discharge corrode? I didn't any problems with the copper.
Why are they exposed to 'wild' temps? And what exactly did the discharge corrode? I didn't any problems with the copper.
is consider 20-98 degrees Fahrenheit a wide variation compared to what I normally deal with which is consumer electronics that live inside peoples homes. I’m not sure what temp the ecu actually gets to in use, the car is blowing the interior air over it, but the ecu itself is not vented so the internal temps could be 95 degrees. I know the instrument cluster board gets pretty hot in use.
It is odd that the problem only seems to affect the 97 ECM, as it is very similar to the 98:- the capacitors are the same across both. I replaced all of them in mine as PM: https://www.jaguarforums.com/forum/x...6/#post1806456
The old ones all appeared to be physically fine, but 24 years is a stretch for electrolytics - even good quality ones - as at best they can dry out and their electrical characteristics deteriorate.
At worst (courtesy greenforest56):
The module housing fan was superseded at some point, so that may or may not be relevant?
1997 XK8 dead again! RESOLVED
