Cylinder specific misfires

[Aaron]

I have a 2005 Kia Optima EX 2.4L (4 cyl) with A/T, USA. My check engine light came on and was reading p0300 thru p0304. I changed all spark plugs, plug wires and ignition coils. Looked for vacuum leaks and found nothing. Removed and cleaned PCV. Cleaned MAF and throttle body. I drove it for about 125 miles before check engine light again. Now it reads p0300, p0302 and p0303. Again checked for leaks and found nothing. Changed EGR valve and drove 85 miles before check engine light with random, 2 and 3 misfires. I have switched ignition coils and fuel injectors around to rule them out.

On the highway the car will sometimes start shaking and will not accelerate when I push pedal. This is accompanied by the check engine light. I can let go of the pedal and then push again and it usually goes back to normal.

I got tired of trying to figure it out so I took it to my mechanic and he looked at it for a few hours and couldn’t figure it out. He ruled out spark plugs and fuel injectors. He didn’t have time for compression or fuel pressure tests.

My question is could a bad fuel pump or fuel pressure regulator cause only cylinders 2 and 3 to misfire? Seems like it would affect all cylinders. I have reset computer (by unplugging battery) 4 times and the last 3 have all been misfires in cylinders 2 and 3. Is it possible this is an electrical problem (cylinders 2 and 3 share an ignition coil)?

Thanks

Topic

[college man]

I would test actual spark on these cylinders. Try doing a power balance test with the injectors.
more in this link.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Author]

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