Problem: P0302 Vehicle: 2011 Mazda CX-7 Steps taken so far:
- Replaced spark plugs
- Swapped coil packs to see if the misfire would move to another cylinder
- Added fuel treatment
The car had an extremely rough idle before the fuel treatment. Now the car has a very smooth idle post treatment (Seafoam + Techron).
The STFT is -5.5% idling and LTFT is 3.1%.
My theory is that there is a dirty injector or the misfire is due to the fuel system because the idle improved significantly after some fuel treatment which is not completely because I am still driving on the same tank I.e., I haven’t gone through all the fuel treatment.
The misfire is neither audible or physical, and I was very surprised for the code to come back after driving another for a day and a half.
Now try swapping the injector for cylinder 2 with an injector for another cylinder to see if the miss moves with the injector.
Tester
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Ask your shop for an injector balance test. That will quickly tell if there remains a misbehaving injector.
On my late 70’s VW Rabbit if I suspected an injector problem I’d pull all the injectors and test them one by one, look at their spray pattern, measure the volume of fuel sprayed in a given time, etc. I didn’t ever find a faulty injector; the cause of the problem was usually a sticking fuel distributor, something which your car doesn’t use. If you don’t want the injector balance test, you could continue with the injector cleaning treatments, hopefully that will solve it. Another idea is to hire a shop to use their specialized fuel system cleaning equipment to feed a professional type of injector cleaner into the fuel rail as the engine runs.
I’m presuming the misfire stayed on 2 after you swapped the coils. Pretty good chance then that the problem is injector number 2. Try swapping injectors, visual check of wiring harness from PCM to injectors, noid-light test, etc.
Perform a compression test, the PCM will detect low compression before you will notice.