2004 Expedition 5.4 #4 & #8 misfire after new plugs/boots


jwalker1970
06-15-2017, 03:50 PM
I'm working on a 2004 Ford Expedition E/B 4x4 5.4L

We recently did a body-off engine swap. New engine fired up run excellent but had an intermittent miss. We discovered water in the back two plug holes (from being pressure washed by the auto recycler).

I decided to do new autolite platinum plugs and new coil boots & conductor springs. I cleaned each coil spade and dabbed with a q-tip of di-electric grease on each end of the conductors.

Installed all 8 coil boot & plugs and dead cylinder misfire on #4 and #8 cylinders (the furthest back & toughest to get to).

I swapped coils & boots from different locations and problem still stayed on #4 & #8.

back cylinders have about 190 lbs compression.

plugs pull out and smell of gas.

coil boots & spark plugs fire out of the engine.


PLEASE HELP!! I'm at my whit's end!

Also: idling 5 minutes will not set any codes.

65comet
06-15-2017, 07:26 PM
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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