THE CAR RUNS PERFECT AFTER I CHANGED ALL 6 COIL ...

2005 Cadillac STS

Tiny

terrydickerson

November, 2, 2012 AT 6:20 AM

The car runs perfect after I changed all 6 coil packs and spark plugs 2 weeks ago. And then all of a sudden Im getting a missfire in one of the cyclinders what would cause this im suspecting that the fuel pump is going out. Im working on a 2005 sts cadillac 3.6 lit. Thanks Terry.

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Cj7

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1 Answer

Tiny

caradiodoc

November, 2, 2012 AT 6:40 AM

Check the fuel pressure if you can feel the misfire. The Engine Computer will detect misfires that you can't feel. For those, the injectors are a more likely cause. Chrysler buys their injectors in flow-matched sets from Bosch and has almost no trouble with them. GM has a big bin full of them, and they guys just grab a handful and stuff them into the engine on the assembly line. After many miles the flow rates change enough that one cylinder is much more lean than the rest. That extra unburned oxygen can be detected by the oxygen sensor and that tells the computer that entire side of the engine is running lean, so it commands more fuel from all the injectors on that side.

Do an internet search for "Jim Linder" in Indianapolis for a better description of the cause and fix. Basically it is to install a set of rebuilt injectors that are flow-matched.

Also, don't overlook a new coil failing. Brand new parts have a greater chance of failing than ones that have been working well for a long time. You can also switch, ...

By the way, how do you know you have a misfire? Is the Check Engine light on and you read the stored diagnostic fault code, or do you just feel it? If you have a code for "random cylinder misfire, go back to fuel pressure. If you have a code for a specific cylinder, say number 1 for example, switch the coils between cylinders 1 and 2, and switch the injectors between cylinders 1 and 3. If the computer sets a new code for cylinder 2 misfire, you know it's that coil. If the code is for cylinder 3, you know it's the injector.

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