Car Backfiring


I have a 1990 pontiac firebird 305 tpi. It is backfiring out the exhaust. I have change the plugs, wires, distributer cap & rotor, added injector cleaner. It has a new remanufactored ecm unit. Im stuck! can anybody help? ~ Kurt ~


Have you checked the timing?


Yes, 6 degrees


yes, 6 degrees


Are you sure the plug wires didn’t get crossed somewhere?


Did it run right before you worked on it?


Did you check the ignition timing with the test connector grounded though?
Backfiring out the exhaust may mean the timing is retarded too much.


Good point. I looked up the procedure for putting it in base timing and the procedures are different for a engine with a carb and a fuel injected engine.


Yes, I did check the timing by disconnecting the timing advance wire. I was reading in the chiltons hand book about the emissions air pump diverter and valve. what do you think about that? could that be a possability?