On a 92 LT1 vette (same ECM as a 93 Camaro), could a bad ECM cause the engine to idle rough and run rich without throwing codes? Watching with Datamaster, the Short Term and Long Term counts keep dropping down to 108 and I get a popping through the exhaust at idle. It has new O2 sensors, new plugs and wires, and all the sensors (MAP, IAT, Coolant Temp) seem to be reading correctly. I guess my last thoughts are opti, ECM, Ignition module, or coil. You can also hear it missing or popping through the exhaust if you rev it to around 3,000 from idle and hold it there. Any thoughts?

 

If you have missing, then the O2 readings are going to be off ... Computer problems are rare.

 

Can I email you a Datamaster scan to look at?

 

Got a way to post a .csv file? There are lots of good people on here that can look at it. I'm not the foremost authority with them.
Like I said, if you know you have a miss, you need to correct that first, as it will affect your log readings.

 

I have a csv file I can email to anyone. Not sure how to post it up for people to look at.

 

I was working with the car today and was using datamaster, and when i shut the car off, i tried to restart it and every time it would run for 2 or 3 seconds then die. i unhooked the datamaster cable and after about 2 or 3 more attempts it fired and stayed running. I tried this again later and one time it just cranked for about ten seconds without firing. The car was firing the ignition, had good fuel pressure, but would not stay running. What could be causing this? Also, it still runs rich at idle and pops through the exhaust. However, if i shut it off, and restart, it runs better in open loop until it hits closed loop again, then runs rich.

 

Did you ever find a fix? My 93 Vette is doing the same thing. If your PCM is bad you may be screwed. I heard it's really hard to get BCM and decent ECM's(No. 16159278) for the 92-93.

 

I picked up another ECM from a friend to try. I will let you know if that fixes it when i get back in town and can try it.

 

Well, I got ahold of another ECM and another EPROM (from a Camaro) as well. I tried the new ECM with my EPROM and the camaro EPROM, and the car still has the same problem. In watching it, I noticed that my O2 sensors were hanging around 700 mv right before it went to closed loop. They weren't varying much until it went to closed loop is this normal? Also, when the car is running bad in closed loop, I can turn it off and restart it, and for the 30 seconds or so that it is in open loop at startup, it idles fine. Then it runs rough as soon as it hits closed loop. Could this be a leak at the exhaust manifolds causing a false lean and having the computer dump alot of extra fuel in?

 

You wont see the o2's move around until they heat up. There not being used in open loop anyway. My car is doing the EXACT same thing now.

 

As soon as it hits closed loop, my Short Term's drop like crazy down to 108 or lower. This means it is running rich and trying to pull fuel, right? The more i think about it, a vacuum or exhaust leak wouldn't cause this. It would cause Fuel Trim's to be above 128 and the car would run rich.

 

You should be able to download a datalog of my car running here.

http://www.filefactory.com/file/65a6b0/

 

anyone???

 

I have been through hell and back with my setup and I can almost say Ive got this problem in my sites thanks to Ion (MadZ28) and constant datalogging. If I was you I would look at the temp switch on the water pump again. I'm having the same exact issues so I found it best to address each issue first before going to the computer and tuning because if the sensors arent right and or mechanical issues are present no tune or comp will help. I tried to download your file but it wont let me so if you want to send it to me go ahead or at the very least ask someone like Injuneer to take a look at it and give you his opinion.