misfire

2004 PONTIAC MONTANA
120,000 MILES
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BRADLACH
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had a misfire problem about a year ago that went away when i replaced the plugs and wires. now it is misfireing again but worse. i was told that it was probably a coil but there are 3 seperate coils and im not geting a code telling me whitch cylender is missing. how can i tell what coil to replace?
Aug 26, 2011 at 6:47 AM
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JDL
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Do some testing, don't replace anything,yet. Use a digital multimeter. One lead just touches the spark plug wire, you don't take the plug wire loose or penetrate the insulation, just touch. The other lead goes to engine metal/ground.
The meter reads an inductive voltage, sometimes it's around 1/2 volt. As an example, if four plug wire read around 1/2 volt and two read zero, I know where to start looking. You have to be careful suspecting a coil, I've seen faulty ignition modules, that would fire two coils and not the third one.
Sep 2, 2011 at 8:22 PM
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JDL
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Just to add, what if the problem isn't spark? Check spark--fuel, use a fuel pressure gage. Then, check compression.
Sep 2, 2011 at 8:25 PM
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