Questions and Answers

Chevy Blazer Ran Nice, The First Time Q. Hi Vince ! I own a 1989 Chevy Blazer with a 4.3 automatic, 2 wheel drive. The problem that I have is that I have always had a rough idle . I have been to more than one shop to have it looked at and no one is able to find the problem. I have replaced all sensors, complete distributor, New plugs and wires.

I also had a compression test done, scope, timing and I was told it's all fine. Now, the thing that confuses me the most is that I went and bought a new ECM. When I installed the new ECM and started it for the first time it ran like a new car. So I went for a drive and it drove beautifully but my "check engine light" came on. I took it home and shut it off and then proceeded to check for errors. I got a bad O2 sensor reading. So deciding to go out and buy a new one, I started her up and it ran rough again. I put a new O2 sensor in it but the problem still exists.

To this day I can't figure out why it would run so great when I installed the new ECM and started for the first time and poorly after. Your insight on this problem would be greatly appreciated.

Completely stumped

A. When you put the new ECM in you had a clean slate as far as fuel strategy goes. The ECM learns what fuel control that particular engine needs to be "happy". You may have something going on with fuel pressure or injectors that was erased with the installation of the new ECM until it ran and re-learned a bad habit. To prove this point, unhook battery for 15 minutes and restart to see if it runs good again. If so, I would suggest you have it scanned by someone who knows what they are looking at to try to find your problem.

Additional Information provided courtesy of ALLDATA