Hi, I do not know much about the ECM's on these cars or much about electricial stuff. I need some serious assistance.

I have a 1991 Z28, car had an original 305 engine. over the years someone swapped in a 5.7 and did all the necessary work. The car is at my friends garage, and we are having a tough time figuring out what the problem is.

when the car is cold and we start it up, it revs at about 2000-2350 RPMs. when it warms up a little it drops to no less then 1500. We hooked up several scanners, SNAP-On, AutoXray etc and not one will connect to the the ECM. I believe it to be a BAD ECM but don't want to spend money for no reason. How can I confirm it is a BAD ECM? when we can the only mode we can get to is field test. We did the Port pin JUMP and the code was 12. (but I only looked for a moment). we pulled the ECM out and noticed the PROM was not seated all the way so we reseated that and still could not communicate with it.

Please help in trying to figure this out.

 

Isn't inability to connect just as likely a bad connection as a bad component?

 

 

Pin M (orange wire) should have close to 5v. If not, then yes, Ecm is definatly bad. You can confirm for sure by testing pin BA8 at the ecm itself with a multimeter.

 

Since This car was originally a vin E 305 tbi car. The tbi serial data line went to pin E of the aldl 160 baud. The 730 ecm you now have is at a faster baud rate and the wire from the ecm pin A8 goes to pin M 8192 Baud. I I think your lack of communication is the serial data line in the incorrect spot.

https://www.thirdgen.org/forums/elec...t-working.html

https://www.thirdgen.org/forums/elec...92-camaro.html

 

Nothing in the OP posts state that this car was originally a TBI car... But if it was, then you are correct about needing to move the ALDL connector terminal.

RBob.

 

Yes it was a TBI car.

 

I was using my sixth sence

 

Test the pins at Aldl connector first with your meter. Either pin e or m then if still don't have close to 5v the ECM is bad. Very simple

 

It turns out that it was the pins. Before we knew what we were dealing with my friend changed the PIN from M to E, this was before we knew that there was a 350 in it not a 305. Once we started pulling it all apart to find out why no communication we took the computer out and the Prom was not seated properly, fixed that and it was still driving us nuts. I told him that we need to swap the pins and he said that he swapped it to E before we knew it was a M, and didnt realize that he changed it. Once it was swapped, we got communication and NO errors, codes or anything! runs like a champ. Now we need to fix the Speedo and tach.

Thanks for the help