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Engine Backfire

Need Help diagnosing unusual problem. 95 Mustang 3.8 (6cyl) began misfiring on cyl 3. Mechanic said probably electrical. Replaced ignition module, spark plug, and wire. Still bacfires. Replaced fuel injector. Same thing. With plenum and throttle body off, compression testor installed in #3, ignition disabled, and fuel injector un-plugged I turned the started and backfire still occurs (compression was 150lbs) up through intake manifold. I even stuffed a rag in #3 intake port and the rag blew out during engine turn over. What can this be? Any ideas?

Reply to
mistermister
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"mistermister" wrote in news: snipped-for-privacy@localhost.talkaboutautos.com:

disable the spark on cyl 2... bet it doesnt backfire anymore

Reply to
Backyard Mechanic

Hi

You cannot backfire when doing a compression test because all the plugs are out and the tester is in the cyl under test. Check all the cylinders and tell us the readings.

Fred

Reply to
Fred V.

Back in the 60's a friend of mine had a 59 Pontiac with a 389 in it. Had a bunch of stuff done to the engine including 13.5 to 1 pistons. We were trying to do a hot compression test and it fired and broke the compression tester. I was holding the gauge and fire shot out of the hole:) All we could figure was it pre-ignited. All plugs were out and the ignition was off. About two weeks later we pulled the pan and all the rod bearing were down to copper. Had about 500 miles on it. So we pulled it down and went to 10.5 to

1's. Solved the problems.

Al

Reply to
Big Al

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