My friend came to me with engine problems. The car had problems at idle and normal driving. I hooked up the scan tool and the ecm was going into closed loop. That is not right I thought(because he has been running w/o an O2 sensor for a long time). So I looked at the O2 MV and they was 1070 or something like that. I figured the O2 wire going to the ecm was catching voltage from something. So I pulled that wire from the ecm connector. Still had 1070mv. I though that is fine because I'll just find a way to force open loop in the chip. After thinking about it some more I realized that I shouldn't have to take additional steps to keep it in open loop. So I decided to swap ecms with mine and the (MV read normal 445 I think). So that was the problem, bad puter. No codes or anything. Guess voltage was leaking from a different circut on the board or something. Makes me thing it was more that 1000mv but that is the max MV the ecm can read for O2 input. Figured I would post this to help other that might have a similar problem...

P.S. I don't have time to proof read this.....

 

Now I have questions Is 10XXmv the max an ecm can see for O2 mv, if so then where is the location in the code for that limit? WHat do you guys think caused the ecm to fail? I'm thinking about repairing it since he is going to throw it away. Figure that in 20 years or so the ECMs will be very hard to find. Learning how to repair em might be a good idea. Last thing I want is to have a useless car because I cant find an ecm!

 

Might try some connact cleaner in the connector cavities, and disassemble the whole unit, and make sure the harness header to PCB is also clean.

Start collecting them now. I have a small inventory of spares.

 

That made my heart drop, it confirmed what I have been thinking..I'll try to grab it from him. When I get it I'm sure there will be some questions to ask. Maybe with some help from you guys I can fix it and document what it took to repair. Eventually it would be cool to have a database of information when it comes to ecm failure. Hmmm, diy-ecm repair.....I can smell that coming along someday...

 

Can you get a schematic of the ECM? I would start looking for leaky caps on the input line first, or anything that ties that line to a B+. This is other then what Grumpy said about clean connectors. Some carbon or corrosion hiding under something will give you leak over to other traces.