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Old 06-15-2017, 07:26 PM   #2
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Re: 2004 Expedition 5.4 #4 & #8 misfire after new plugs/boots

There has been a problem with the alternator. The diodes can fail and it starts to leak too much AC voltage that can cause misfire readings to the PCM and it tries to compensate. The DC readings will be fine and the testers at the auto store don't always pick it up. On YouTube there's videos of Mustangs with the same era problem and how to check for it.
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