Hi,

Last night whilst driving all of a sudden the SES light came on and engine completely bogged down and would backfire when trying to accelerate.

I immediately pulled over, turned the engine off then checked for codes.

CCM returned C41, and ECM returned H51.

I started the car up again after turning off the battery and car ran fine, I did the tap test on the ecm, which instantly recreated the stumbling engine and SES light.

I managed to get the car home as I was very close, and this morning went through the diagnostic in the FSM, which said to bring the computer into module 4.1, and there was no "ERR" displayed, which means the connection is OK, and not something in the serial bus, is this correct?

I then proceeded to remove and replace the PROM from the ECM, after doing so, the engine started up fine and was running perfectly, until I shut the engine hood. That cause the same problem to reappear, and I assume this is because the force of the hood impact rattled the ECM.

Is this the sign that my ECM needs to be replaced? Is there anything else I should be checking? Is there any chance that the PROM could have been damaged, or are they pretty robust?

I am in Hong Kong, so I will have to order everything from the US and want to make sure I'm getting the correct parts.

Best regards, and thank you in advance!

 

Some reading
Post #33 especially
http://forums.corvetteforum.com/c4-s...-or-ccm-2.html

http://forums.corvetteforum.com/c4-t...wes-is-me.html

 

What year is your car?

 

Its a 1991, I put it in the subject line when I posted, sorry I should have put it in the message as well.

Cheers

 

Thanks for the links, I read those, and they all seem to point to a faulty ECM... I guess the only way is for me to replace it, I just found some rebuilt for 90-91's at ecklers for about US$115. Should I give it a shot?

 

I would give the harness a good shake first and pull the connector one at a time and spry some contact cleaner into Same goes for the prom chip and any device the codes refer to as corrosion can cause a bunch of problems that look like bad components. For 10 bucks and 15 minutes it has to be worth a try.

 

I hate buying parts I don't need. It's worth running down the alternatives first.

 

Thanks will give it a shot, is it safe to spray contact cleaner onto the prom?

Cheers

 

Tried unplugging all the ECM connectors and the inside sockets looked like brand new, and so did the internals of the plugs.

Anyway I cleaned them with contact cleaner, re installed them, plugged in the battery and gave it a shot.

Car ran fine for a minute, then I tapped on the ECM, then all went bad again...

Im leaning on this being a bad ECM, as I will have no means of testing a short or an open here.

 

If you have other wheels, you can take the ECM out and have it tested, or you may have to send it.

 

Replacement ECM arrived today, and turns out it was the culprit after all.

Going to send this original one back to the US, have it rebuilt and kept as a spare.

For anyone else going through this issue, I did have some problems with the replacement ECM at first.
Luckily I had the FSM on hand to read through the procedure, and two important facts were to make sure the PROM was seated and the side clips fully snapped into place.
At first when I started my car with the new ECM, it wouldnt run more than a second or two. The FSM stated once re installing the new ECM to enter diagnostics mode and wait for 4 code 12's to flash before starting the car for the first time.

Cheers and thanks for the previous responses.

 

The 91 ECM is a common GM part used on about 10 other models. I picked up a junkyard piece from an 89 Oldsmobile and it was a GM rebuilt. These things are not as reliable as you would expect a solid state device to be.