My 1989 Grand Am with the 2.5 Iron Duke with 90,000 miles on it backfires at 1/2 to 3/4 throttle. I have replaced most of the sensors on the thing except the MAP and the TBI injector. The O2, TPS, Idle sensor, crank position and the Ignition control module are new as well as the ECM. Spark plugs are AC's new and gapped at .060 and the plug wires are new high heat silicone 7mm. Motor runs really well with normal driving but if you need to pass a car she backfires. Put the pedal to the floor and she goes w/ no backfire. Only between 1/2 -3/4 throttle. Running out of things to replace. Please help.
Nov 20, 2007 at 8:56 AM