Question about 1985 Cadillac DeVille

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Backfiring through throttle body

85 cad 4.1 backfiring through throttle body. replaced wires,plugs,cap,rotor,same problem has strong blue spark on #2 and #8 plugs #4 and #6 spark, yellow and very very weak can hardly see it where the other plugs you can hear it and watch it jump 3 inches . could the coil or the ECM be breaking down and causing this? this one has me puzzled. I have had this before on different cars and one the cam lobe was wiped off and one of the others the rocker arm had come off the push rod and and have seen bent push rods cause this problem,but no fire or hardley any fire on 2 cylinders seems funny. any ideas? thanks in advance
MP

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Have you found the problem yet? I am having the same issue and was wondering if you had any progress. Thanks

Posted on Oct 29, 2008

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It could also be that either the timing chain jumped because of worn teeth or the gear on the distributer might be worn as well . i would check this first. you can always pull the valve covers to check the rockers to make sure they are not real loose, but chances are you would have noticed that right away. if it were the coil you would not have a strong spark on any of the cylinders and it would probably real hard to start. due to the age of the vehicle it's possible the ecm is on it's last leg, but before i would look at that i would check all the other things first. if it is the ecm you can get a used one at a salvage yard for around 200 bucks . it will cost you a mint at the dealership. hope this helps. please rate this thanks.

Posted on Sep 01, 2008

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