Scanned Computer-What can I do now?

[bad64chevelle]

OK I got the scanner today and found two stored history codes.

1)41-Ignition control circuit, open
2)42 - Ignition control circuit, grounded
3)51 - EEPROM program error

Now to the symptoms.

The car stalls out of nowhere-as Jeff saw today at his house. It will stall at idle in park, in gear, at lights, or going down the road. It always seems to be when i try to accelerate. Its a intermittent problem too. Happens witout warning. Please if you have any idea for where i can start now, let me know. Thanks

Jon

[Tru2Chevy]

I don't know much about the LT1 ignition system (besides signs of failing opti), but do they have some sort of standalone ICM? If so, maybe it's messed up.

Not sure what EEPROM Program Error is though. Can a file on a chip get corrupted?

- Justin

[foff667]

i would talk to prevost...with eprom error in there he might be able to help diagnose your issues.

[bad64chevelle]

OK thanks guys. I am looking for my one buddy today with a 94 Z28 A4 so maybe we can switch computers real fast and see if my problems go away. Until then, i will begin to research this a little more and if Prevost reads this, please let me know what you think. Thanks alot guys...some day this thing will be back to full strength...

Jon

[Injuneer]

Clear the codes by pulling the "PCM BAT" fuse on the panel at the end of the dash for 30 seconds (key "off"). Â*See if the codes come back. Â*I think the EPROM code sets when their is a checksum error. Â*DTC 51 is rare with the "fixed" chip 94 and newer PCM's, since the most common error is cause by poor insertion of the chip, which is a problem more with the 93 and earlier ECM's.

As far as the DTC 41 and 42 codes, its a problem somewhere in the entire ignition system made up of the Opti, the IC Module and the IC signal that goes from the PCM to the ICM. Â*

I have the logic tables for diagnosing the codes, and can fax them to you if you want. Â*They are fairly complex because there are so many components involved. Â*Shoebox may actually have them on his Tech Pages website, as well.

[bad64chevelle]

OK, I have just recently replaced the opti, and the ICM. The PCM has been reset after they both have been replaced. I hope they are not going again. What i will do is reset everything again, and get a new ICM and put it back in and see if this continues. I do not have a fax, but will check shoeboxes site when i get a free minute. Thanks

Jon

[Fasterthanyou]

I concur with Injuneer. The 51 error is really odd and might require the flash chip to be desoldiered from the board. If so, and you do need a new ecm let me have this one and I'll see if I can repair it.
As for the other 2 errors, sounds like you forgot to hookup a control wire between the ignition module and the pcm. This would cause the ignition to go into backup mode and run very mild spark advance with crude "slopes". The major problem is the 51. What's happening with a current code 51 (the code does get stored for a while) is that the pcm just uses the RFD (bunch or resistors) to do the fuel calculations.
Pull the pcm, get a multimeter and do the voltage/resistance check on everything according to a service manual. That's always the easiest way of chasing down a wiring problem.

[bad64chevelle]

OK, well all the wires that were originally hooked to the stock icm were rehooked when i got the new one. Im almost like 100% positive of that ill check though. I will pull the pcm and do the tests tomorrow if its not raining like crazy. Could you give me prices of how much it would cost me for you to fix it? Thanks
Jon