Chevrolet Repair: chevy 3.1L engine miss at times, air fuel mixture, cat converter

Question
1992 chevy baretta 3.1L  got this car for free from friends, ran very poor.  new plugs, new plug wires, new cat converter, runs better but still have this problem

Engines miss, worse under load, popping in exhaust ( like low backfire noise ) at idol and when driving at times

no engine codes, consistent condition. Please advise  

Answer
Hey John,

  How did all of the plugs look when you removed them?  Did one in particular look worse than the others?  If there is a popping noise under load that could be the air fuel mixture igniting inside of the intake manifold.  This can happen with a valve does not seat properly due to carbon or a burnt intake valve.  Do a compression test first and make sure all of the cylinders are within specs and even accross the board.  If one is low you can pressurize it compressed air and listen to the throttle body and exhaust to see what is not sealing properly.



Wayne