I have a problem with the primative ECM on my 81. Not too long ago we installed a GMPP 350 HO engine in my 4 speed 81. We kept the Q-jet, distributor and exhaust from original underpowered '81 engine. Wanting to extract a bit more power I installed a set of Patriot short-tube headers, true duals and Magnaflow mufflers. It runs and sounds great --- when it runs! Though I feel rather ignorant to admit it, as a result of the most recent exhaust upgrade the engine runs horribly at anything less than full throttle. I am almost positive that the problem is with the ECM which is not hooked up to any exhaust sensors and is throwing my spark curve/ignition timing way off. As I see it I have only two options. The first is to install new sensors (and I know not what else) to make the distributor conform to the modifications. The other option is to strip the car of the entire ECM system -- installing a new carb and distributor. Have any of you who have '81s had any similiar problems? If so, how did you remedy the problem. Thanks much.

Jay

I have a problem with the primative ECM on my 81. Not too long ago we installed a GMPP 350 HO engine in my 4 speed 81. We kept the Q-jet, distributor and exhaust from original underpowered '81 engine. Wanting to extract a bit more power I installed a set of Patriot short-tube headers, true duals and Magnaflow mufflers. It runs and sounds great --- when it runs! Though I feel rather ignorant to admit it, as a result of the most recent exhaust upgrade the engine runs horribly at anything less than full throttle. I am almost positive that the problem is with the ECM which is not hooked up to any exhaust sensors and is throwing my spark curve/ignition timing way off. As I see it I have only two options. The first is to install new sensors (and I know not what else) to make the distributor conform to the modifications. The other option is to strip the car of the entire ECM system -- installing a new carb and distributor. Have any of you who have '81s had any similiar problems? If so, how did you remedy the problem. Thanks much.

Jay
my 81 w/ 383 stroker 500HP . now has Msd ignition w/ curve , Quickfuel SS 750 carb, might be much for yours a 670cfm probably do nicely. retire the smog gear

I have a problem with the primative ECM on my 81. Not too long ago we installed a GMPP 350 HO engine in my 4 speed 81. We kept the Q-jet, distributor and exhaust from original underpowered '81 engine. Wanting to extract a bit more power I installed a set of Patriot short-tube headers, true duals and Magnaflow mufflers. It runs and sounds great --- when it runs! Though I feel rather ignorant to admit it, as a result of the most recent exhaust upgrade the engine runs horribly at anything less than full throttle. I am almost positive that the problem is with the ECM which is not hooked up to any exhaust sensors and is throwing my spark curve/ignition timing way off. As I see it I have only two options. The first is to install new sensors (and I know not what else) to make the distributor conform to the modifications. The other option is to strip the car of the entire ECM system -- installing a new carb and distributor. Have any of you who have '81s had any similiar problems? If so, how did you remedy the problem. Thanks much.

Jay

You'll be much happier dumping the original carb and distributor. I had an '81 Z28 with that junk on it and I ended up putting a 400 in it and was going to keep the distributor/carb. I too left the ecm in and eventually dumped it for a Holley 750, and an MSD HEI with no ecm. The problems I had went away as soon as I fired it up. If I had it to do again I wouldn't even mess that 'junk' and go straight to the setup I ended with. That car was a screamer once I got it all sorted out.