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Backfires

Tiny
TIMVDB
  • MEMBER
  • PONTIAC GRAND AM
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.
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Tuesday, November 20th, 2007 AT 4:56 PM

3 Replies

Tiny
TOBYU
  • MEMBER
  • 89 POSTS
If it was a MAP it should pop a code.
Get an meter and check the TPS for a flat spot near thet throttle position.I have had a couple of GM that had no TPS codes.(22). But a new one fixed it up.
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Wednesday, November 21st, 2007 AT 6:28 AM
Tiny
TIMVDB
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  • 5 POSTS
I will check the TPS allthough I just put a new one on it. I did pull a trouble code from the ECM this morning and it was a 32. EGR Valve?
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Wednesday, November 21st, 2007 AT 11:22 AM
Tiny
TIMVDB
  • MEMBER
  • 5 POSTS
The problem was the ignition coils. Coil for cyl. 2-3 was arcing internally between each other which could not be seen from the outside. Also, will not throw a code so something for you all to watch for. Sound to me like these coils are culprits for a lot of mysterious problems that turn up.
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Tuesday, December 4th, 2007 AT 8:55 AM

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