Hi I have a 1987 Trans Am completely stock and original with the LG4 305 computer control carbed engine. The carb was recently professionally rebuilt by Mountain Man Fuel systems and has all new components. The car ran great until just recently.

Here are my issues:

When I run the car it stays really really rich as if it is in "limp mode". The mixture control solenoid does not dry cycle when turning the ignition on. I also cannot get any communication at all with the ALDL port via a snap on scanner ( the scanner would get power) or by jumping pins A and B and the SES light will not light up or flash at all.

My findings:

I have confirmed my SES bulb is good. But I will never see it light up at all.

There is power and ground at the ALDL port.

No MCS clicking

Car seems to be in constant "limp mode"

I have confirmed I get constant power going to the ECM and power switched on by the ignition as well as a ground.

I have completely ran the car with the ECM disconnected and the car runs the same and no SES light appears.

I feel like the ECM and or PROM is dead.

All the pins on the ECM appear to be making good contact and the PROM is seated correctly.


My main question is, does this all point to an ECM and or PROM issue?

The car is or now was my daily driver and I need to get it back up and running as soon as I can. Will a new factory rebuilt ECM and PROM most likely cure this issue?

 

Found out my Prom was bad and the Light Driver Module for the SES light was bad.

 

most likely cause is loss of power to the 'engine controls'. the mcs, tps, egr solenoid, etc. do not receive power from the ecm. the power comes through the controls fuse. the ecm controls these components by providing a ground.