Going to repost this here, since it not getting much play over in the ECM board.

So, for the past 10 months my 91Z has had multiple issues. First the speedo would randomly stop working, with SES light on. Car would rund horrible and very rich when this occured. Swapped out VSS and speedo gears. Problem continued. Then I would get hard starting, " double peddling" to keep car running at low rpms, and it would randomly hesitate/die out at highway crusing. When this happend, it would take a few times to restart. Then it would run kind of ok again. Sometimes it would run for 1 minute... sometimes 1 hour.
I have checked the injectors, map, fuel pressure and vac lines. All (seem) good. I have hooked up ALDL cable with TunerPro and it said connected but would not read any data. I have tried jumping a&b on the port, and I am getting no codes. It doesnt even seem like ECM is going into diag mode (no code 12). So now I am thinking that the ECM is shot.
Like I said the car is a 91Z, 305tpi, bone stock.

The one response that I got was that it sounds like the ecm is gone, but before I go buy another one, would like some input on what else it could be.
Thanks.

 

does the CEL come on when you turn the ign switch to run? if it does and you cant even get a code 12 when you jump the ALDL. I too would suspect the ECM and or the MEMCAL.

 

Yeah. Ses/CEL light comes on and it is steady. I am going to pull the ECM this week and play around with it. I was able to find a reman GM replacement if needed for around $130 with a 3 year warranty.