Have a 90 Firebird auto that from time to time the tach and speedo would go dead and the car would run rough. Sometimes after driving it for an hour or more and shutting it off the starter would be dead for 15 min or so (jumping the selenoid by screwdriver would crank and start it). Became progressivly worse untill it began dying while driving and stranding me. I had a 91 Corsica 3.1 some years back that acted the same and when it died for good I replaced the ECM and it came back to life. The first ECM I put in the bird started it a couple of times but it ran very rough and smoked. The second one is a bit better but the car idles very low, eventually dies, and will not start again for hours. I have put the original ECM in and gotten it to start twice and it idles and runs like it used too (just no long trips!). The numbers match on the boxes, and the fuel pump was replaced two years ago.

Any suggestions? Would love to drive it to Northern Idaho tomorrow rather than trailer it...

 

Do I need to reset the new ECM somehow other than just unplugging the battery cable? I started it last night to try to drive it onto the trailer and it only ran for about 30 sec. before it died. Would this be enough time to provide any usefull error codes? Will it damage the unit to trial and error 6-12 or 5-6 jumper? I am going to check for any obviouse loose vac lines or wires when I get back but I don't have a repair book. I'll also pull a plug and check for gas/spark if it runs and dies again. I have already went thru all of the fuses under the dash- are there any to look for under the hood? Anything else I should look for? My battery is kinda old and may weak cause the car has been sitting about 6 months. Could this be a factor?

Great forum, by the way! Learned I didnt know much about my car by reading old threads for a couple hours. If I sound like a complete bonehead it's probably because I am. Now wondering if the chip in my ignition key hasn't been giving me some grief all along.

 

Check your battery connection first. Then check your relays and there's a couple fuses in front of the battery under the fender overhang too. Any amount of time the engine stays running it's reading the sensors and checking for errors. Let it run until it dies then check the error codes. Don't erase them until you've fixed the problem, it's valuable data that helps you diagnose your problem.

 

The Firebird had a long 300mi trip on a trailer. Tomorrow I will go thru the steps outlined above. I read last night about the location of the fuel pump relay and how to test it. If there are any other relays I need to check, where are they and how do I test them? I'll pick up a service book but it won't be till later in the week so please bear with me! Love this car and need it again as a daily but am new to all things more sophisticated than an HEI, carb, and seat belt buzzer. Thanks for the direction bl85c.

 

Ran thru the list except for checking relays. Started the car and ran it for about a minute. I ended up with a diagnostic code of 12 repeating over and over without any following code. Now the car has no spark at the plugs or at the coil. It is getting fuel and while it ran it was running very rich. How should I go about troubleshooting the spark issue? The auto parts store said it might be the ICM. These are about 60 bucks. Hate to start just swapping parts that may be ok.

 

Ok. The underneath of my dist cap was a mess. I cleaned it up but didn't replace anything and (lo and behold) there was spark. The exhaust manifold glowed red after starting it until I took my foot off of the accelerator. Cooled back off at idle (500 to 600 rpm). Diagnostic codes were 33, 35, 45, 66. Just for fun I put my old ECM in and it ran much better. The only code returned was 45, it is running a bit rough. Found a vacuum hose in questionable shape pulling the cap... going to replace it and cap and rotor cap when I go into town tomorrow. I should have come to this forum about 9 months ago and/or just tuned her up. The Basics!! I really appreciate the information here, great site! If anyone has any comment, flame, etc. I'll monitor this thread for another 24 hrs then please consider it closed. Thanks all!

 

Code 12= no errors
33= map voltage high at idle
35= IAC idle speed error
45= O2 rich
66= ecm circuit problem

What this is indicating is that your IAC has gone bad, and that it's running very rich. After you replace the IAC (and since you've switched ecms) you need to clear your error codes, then restart and let it run awhile. Tell us what codes it spits out.

Make sure that there's dielectric grease between the dist module and the distributor. Not coating it could cause it to overheat and pick up alot of rf interference.