I have a 2004 Pontiac series 111,,ive changed plugs,coils wires,electonic ignition plate three times. All of that got rid of the miss,,however now im having a bogging between shifts between 1st and second only. Computer says catalytic converter flow restricted,however,could it be a problem going on before the converter? Could this be the map sensor giving a false read?
Most likely the misfiring has ruined the catalytic converter. When an engine misfires the raw gasoline from that cylinder is sent from the engine, unburned, into the exhaust system where the catalytic converter must "eat" it. When this happens the converter is overheated and destroyed. The "honeycomb" inside the converter has melted and is now restricting the exhaust flow. HTH. -Jim
I have experienced the same issue. The misfire causes raw gas to expel into the catalytic converter and clogs it up. Are you showing any evap codes?
Search Pontiac Grand Prix Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Pontiac Grand Prix Experts