Multiple Cylinder Misfire (P0300, 0301, 0304)

2007 FORD FUSION
105,000 MILES • 4 CYL • 2WD • MANUAL
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BIONICLEADDICT
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Car has no obvious signs of an engine issue (Sounds, smells, mileage, rough idle, hard start).

Check engine light intermittently comes on/flashing while driving, caused by multiple cylinder misfire (always 1 and 4). I've swapped the coil packs, replaced all the spark plugs and all the fuel injectors and the codes stay the same, so the problem seems to be localized at cylinders 1 and 4. Mechanic supposedly checked compression and found nothing wrong, still waiting on documentation.

Misfires always go away in less than 1-2 min. They occur at a much higher frequency on long high-speed downhills in hilly terrain.

Forgot to add, there had been an oil leak/oil leaks in the engine previously, this was fixed.
Jun 2, 2022 at 4:28 PM
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SQM
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Hello,

Those random misfire codes can be caused by a number of components/reasons.
It could be due to faulty fuel injectors, blockage in the EGR system, bad EVPA purge valve, improper fuel pressure, it can also happen due to having low fuel and of course due to spark plugs or coils.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

As you have already done the injectors and plugs, checking and cleaning the EGR system would be a good next step.

https://youtu.be/DqUCbbKdWf4

Are there any other codes besides these random misfire codes?

Let me know of any questions.
Thank you.
Jun 3, 2022 at 11:28 AM
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BIONICLEADDICT
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Thanks for the incredibly thorough response. I'll try to check the EGR system or find someone qualified to do it.

I just picked up an OBD reader today and checked the misfire counts: 148 on cylinder 1, and 175 on cylinder 4. Are EGR, EVPA purge valve, or fuel pressure likely causes if it is very consistently in these 2 specific cylinders?

I am keeping my fingers crossed it is not a head gasket or timing chain issue.

There was previously an oil leak (valve cover gasket, which is right above cylinder 1 coil/plug) and there may be some oil in the spark plug wells. Could that be a cause of misfiring?

Jun 4, 2022 at 3:01 PM
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SQM
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Oil in the spark plug well can cause misfire, which is a common issue for having a valve cover leak. You can always clean the spark plugs out and see that it improves the condition, given that the plugs appear to have oil on them.
Jun 4, 2022 at 3:25 PM