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post #1 of 9 (permalink) Old 12-06-2018, 12:34 PM 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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post #2 of 9 (permalink) Old 12-06-2018, 03:23 PM
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My thoughts are, did you clear the cylinder 3 code after swapping the coil? And, did you run the diagnostic to see what the CEL light was trying to tell you on you 55mph run?

The next thought is to run a compression test and see if cylinder 3 is low. My other thought is that the coils can be otherwise fine by appearance but not work under load and heat. I would probably suggest replacing all the coils if you suspect them at all. I don't have any experience with the injectors so someone else will need to help you there.

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post #3 of 9 (permalink) Old 12-06-2018, 03:27 PM
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Quote:
Originally Posted by waughoo View Post
My thoughts are, did you clear the cylinder 3 code after swapping the coil? And, did you run the diagnostic to see what the CEL light was trying to tell you on you 55mph run?

The next thought is to run a compression test and see if cylinder 3 is low. My other thought is that the coils can be otherwise fine by appearance but not work under load and heat. I would probably suggest replacing all the coils if you suspect them at all. I don't have any experience with the injectors so someone else will need to help you there.
^^^^ what he said ^^^^

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post #4 of 9 (permalink) Old 12-06-2018, 04:05 PM
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Quote:
Originally Posted by waughoo View Post
My thoughts are, did you clear the cylinder 3 code after swapping the coil? And, did you run the diagnostic to see what the CEL light was trying to tell you on you 55mph run?
You beat me to it.
Quote:
Originally Posted by waughoo View Post
The next thought is to run a compression test and see if cylinder 3 is low. My other thought is that the coils can be otherwise fine by appearance but not work under load and heat. I would probably suggest replacing all the coils if you suspect them at all. I don't have any experience with the injectors so someone else will need to help you there.
My coils tested fine as per the procedure below


Replacing them however fixed my mis-fire. I went with OEM (Denso) and plugs (Motorcraft Platinum) but many will likely work. If you can't find anything else...
Have you removed the injector and checked spray pattern?
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post #5 of 9 (permalink) Old 12-06-2018, 04:47 PM
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why don't you move the fuel injector, like you did the coil?
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post #6 of 9 (permalink) Old 12-06-2018, 09:45 PM Thread Starter
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Forgot to add this picture and video of my maxidas scan tool showing the fuel system status for both banks with the vehicle in park and slowly increasing the rpm. With the car at idle, the fuel system status shows open loop for both banks - fault
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post #7 of 9 (permalink) Old 12-06-2018, 09:46 PM Thread Starter
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Also disabled the fuel injector for cylinder 3 with my maxidas and when i did so, the engine did run a little rougher.
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post #8 of 9 (permalink) Old 12-06-2018, 09:46 PM Thread Starter
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Quote:
Originally Posted by RobertD View Post
why don't you move the fuel injector, like you did the coil?
its on my list
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post #9 of 9 (permalink) Old 12-06-2018, 10:04 PM Thread Starter
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Ok this is weird just plugged in my scan tool again and with the car idling it now shows the fuel system status as closed loop where as earlier it showed open loop at idle...
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