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88 electrical problem - rather odd


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I have a bit of an unusual problem with an 88 coupe. Keep experiencing intermittent loss of all ALDL communication (or at least it appears that way) resulting in 00/error on the IPC, service engine soon, electrical problem and radio only (RAP mode) on the CRT, with default HVAC defrost mode. It never lasts long enough for me to go through the troubleshooting tree, so the cause is evading me so far.

However, I have now noted another issue that is seemingly related. Twice now, when shutting off the car (key off and removed from column) the IPC stays on, with regular readout (fuel gauge working, odometer showing etc.) and CRT operating normally (as though car is still on). Opening door did not kill the instrumentation when this occurred either, so it was clearly not in RAP mode.

In light of this latest failure, I am beginning to think a bad ignition switch causing intermittent loss of IGN 3 power feed to multiple modules, and also not always cutting the IGN 3 feed when the ignition is turned off. Wonder what anyone else here thinks of this theory. Prior to finding the IPC would stay on after key-off sometimes, I was leaning towards a RAP related problem (bad relay) but that seems not to be the case now.

Edit: another thing I should have noted is that sometimes the loss of communication occurs with the car already off (so the light show does not work normally, but the IPC will show "electrical problem" and error for the odometer readout when the light show would normally be taking place. So, this may negate the possibility that it is an ignition switch related problem.

Big problem is that I cannot induce the failure so far by the jiggle method (manipulating the wires) and it never occurs on it's own for more than a few minutes at a time, usually while driving so troubleshooting is not immediately convenient. I have spares for all modules, so could start swapping one by one to see if one of them is pulling down the network causing the failure, but would prefer to save that as a last resort as pop and swap is not good troubleshooting practice.

Welcome any input.


Edited by KDirk (see edit history)
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Just a follow up. Appears that replacing the BCM has solved the problem. Worth noting that the BCM I removed was a reman unit.

So, this is yet another ding against reman parts, which have had an exceedingly poor record of service on my cars. Clearly I'm better off taking my chances with salvage yard parts, reman modules seem to be junk more often then not by my experience.

I really wonder how these outfits that do rebuilds on ECM and BCMs can offer this stuff with a straight face. I went through 3 bad rebuilt ECMs on my first 88 before getting one that worked right 100%.

I have to add, I can't even count the number of bogus reman alternators I've been through in 8 cars over 20 years and they are simple mechanical devices, not complex computers.


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