BS430

Misfire in cylinder 4

3 posts in this topic

I own a 97 Mazda 626 2.0L and I don't know why it won't stop misfiring in cylinder 4. It only misfires after its been driven for some time. If it sits for a while it's starts up normal, but eventually starts misfiring. I have checked the plugs and wires with a multimeter and changed the distributor cap and rotor. I had a feeling it could be the fuel pressure regulator, but that isn't leaking any gas out of it. What could the problem be? The next thing I'm going to do is check the compression and check the injectors. What should I check for in the injectors? Any  info right now would be great cause I have no clue what it could be.

Thanks,

Robert

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Sounds like a resistance related issue. When temperature changes, it affects the resistance in the wiring and sensors.

You could check fuel injector resistance on each injector, it's been awhile I can't remember, I think the specs should be 14-16 ohms. If its open or too much ohms, it may be a failed injector.

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Kind of obvious, I know, but if you want to spend the time to make sure it's the injector, you could swap for another cylinder and see if the trouble moves to the other cylinder.

+1 to the compression test - great idea. Also if you have an air compressor, you might consider investing in a leak down tester. I found one for ~$30 on Amazon. It's easy to use and will tell you where low compression is coming from. If it's a valve on cyl 4, that could be the culprit. "Leak down tester" is a fancy name for a gadget that will shove air into a cylinder (thru the spark plug hole) and then you can listen to various parts (exhaust pipe, intake duct, oil filler plug, radiator filler neck) for hissing air to let you know what part of the engine is leaking compression. Exhaust pipe = exhaust valve leak, intake duct = intake valve leak, radiator = head gasket, oil filler hole = worn rings (that's where mine was.)

I had low (-30%) on two cylinders (again, worn rings) - yet the car still runs pretty great - so don't freak out if your numbers are a little bad, it can happen with age and doesn't really mean you have to do a rebuild. If it's pretty low and it's coming from a valve or head gasket, though... that's another story.

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