I have a 1991 Camaro RS with a 383 in it and it has been running fine for years!!! But now I am having a problem with it missing and backfiring. I have put on a new distributor cap, new rotor button, new spark plugs, new spark plug wires, checked my MSD Digital 6 Ignition Box according to MSD (and it is functioning fine) and my car is still missing, popping, backfiring and not running right!!!! My check engine light is not coming on. The car seems to run fine as long as you don't "get on it". Doe this mean I need to replace my ECM??? I have had to have it replaced once in the past but I do not remember the symptoms it was having. Do I need to replace it again???

 

My first best guess would be a fuel delivery problem. Check everything mechanical too, battery cables, ground straps, plug wires. . . As far as the ECM try to get/beg/borrow a known good one and try it.

RBob.

 

Thanks for your reply. I have a fuel pressure gauge in the cockpit and it is reading normal with no variations in pressure. Do you think it could still be a fuel delivery problem???

 

A datalog would possibly show something erratic, maybe O2 took a dump or EST is screwing up.
No easy way to tell without seeing something, although symptoms do sound fuel related.

 

What is a datalog?
What is an EST?

 

Datalogging: Using a cable and a laptop computer to read the serial output data from the cars computer. Readings can/will be of O2 sensor, throttle position, rpm, Manifold Absolute Pressure, yadda, yadda, yadda.

EST is Electronic Spark Timing and is ECM controlled for advance and retard of the distributor.

Connecting should show you what is working and what is not.
Do some searches and reading in the threads to find out how this is done and the hardware/software requirements.
Once you start, you'll never live without it again!

Also Have you considered the fuel filter?
Check the connections on the fuel pump circuit as well.