1999 Pontiac Grand Am Catalytic Convertor
Check the exhaust system for excessive back pressure to rule out catalytic converter, also check the TPS/MAP sensor
Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.
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Saturday, November 1st, 2008 AT 11:36 AM