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post #1 of (permalink) Old 12-06-2018, 11:34 AM Thread Starter
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Cylinder 3 misfire

Working on diagnosing a misfire on a 2004 Mazda 6 3.0. The misfire is on cylinder 3. I removed the coil and plug from the cylinder. Plug looked good and coil had no cracks. Used multimeter on coil and resistance was good. I then swapped the coil and plug between cylinders 3 and 4, put everything back together and started it up.

Plugged in my scanner and cylinder 3 misfire code was still there with no cylinder 4 misfire code. Because of this I know the coil and plug are good. Otherwise, if it was the coil or plug causing the misfire, the cylinder 3 misfire code would be gone and there would be a cylinder 4 misfire code.

Next i used a mechanic's stethoscope and listened to the cylinder 3 fuel injector. It was making a constant clicking noise, but was not as loud as the other injectors.

I then took a test drive. When i was doing 55mph, I came to a downslope so I let off the accelerator. When I did this, the rpm needle kept fluctuating between 2200 - 2400 without me touching the gas pedal. It stopped doing that once I reached the bottom of the hill and got back on the accelerator. At one point the engine began fluttering pretty bad when accelerating and the CEL switched from solid to flashing during the fluttering. I then let off the accelerator and the fluttering stopped and CEL went back to solid.

I was hoping it would be the coil, plug or injector. Is there any additional testing I can do on the fuel injector? Should I do a compression test? Does it sound like a fuel related problem? Is the fact that the fuel injector on cylinder 3 is not as loud as the other injectors enough of a reason to throw a new fuel injector at it and see if it fixes the misfire? I hate tgrowing parts at a car and prefer to find the actual problem

Has approximately 190k miles.
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