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It helps a lot if you actually identify specifically what you're working on.
A P300 means the PCM can't determine the misfiring cylinder accurately or there are multiple misfiring cylinders. Your best bet is to go in and look at the misfire count PIDs in mode 6, test 53 and see if you can get more data. Other faults such as a weak cam sensor or EGR system problems can also cause problems.
Same issue with a 99 F250SD V10. Getting P0300 and P0308. Changed the COP and plug on #8 and still getting the P0308. Found the double split PCV elbow hose in front of the TB and replaced it. Cleaned MAF and ran a tank of gas with Sea Foam. EGR was just replaced by dealer a couple of months ago. LTFT is good but STFT has a delta of 20% plus. Any other ideas?
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