Let me begin by saying that I am new to the forum and thanks in advance for any help. I have a 99 Ford F150 with 116k on the 5.4 liter V8. For over a year everytime I am running about 50 mph (1200 rpms) and lightly accelerating or going up a hill, I experience a terrible miss or chug. WhenI acclerate aggressively it never happens.

As of late it seems to slightly miss when idling, but not enought to drop the rpms. No check engine light has ever come on. I replaced the plugs with motorcraft plugs about 12,000 miles ago and under recomendation by a Ford dealer replaced coil pack #8. Every dealer and mechanic I have been to has not been able to fix the problem or suggest what may be the cause. PLEASE HELP! It is getting terribly annoying.

 

You should start it up at nite and rev it up to check for arcing from the wires. The next thing I would try is cleaning the throttle body. Sometimes the EGR and/or the IAC becomes clogged with carbon. Do a search of the forum, theres an artical here that takes you through it step by step.

 

Sounds like the same problem I was having.
https://www.ford-trucks.com/forums/s...d.php?t=445054

 

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Thanks for the input. A friend and I will try your suggestions tomorrow.

 

i had the same exact problem (5.4 v8 miss at idle and sometimes when driving but only under a load with no svc soon light) check the #4 coil pack. when these trucks get older, they tend to seep from the heater hoses (on the passenger side towards the back) which happens to be rite over the top of coil pack number 4... consequently water drops down and shorts them out.... that would be my first guess anyway.. another way to check would be to take coil pack 4 and put it in the front cylinder and then take the one from the front cylinder and put it in the back to see if you end up getting a light or code or whatever. (the light is just an idiot light and only come on if it is affecting your emissions) thats all i can say to help
-marshall

 

Well yesterday we pulled of each COP, and replaced each plug again. Figured while I had it off, it couldn't hurt. Replaced cop #4, cleaned fuel injectors, and everyother part. Still missing and now it seems even more steady than before. Don't know what else to do with no code being thrown. Still open to any suggestions. Thanks.

 

I had, what sounds to me, the same problem with my '02 S'crew w/5.4L. It started at about 60,000 miles and it now has 98,000 miles and still doesn't show any "codes". I've replaced the plugs and COP "boots" and it helped a lot, but it is still there every once in awhile. I've had it scanned several times w/o any codes. As my mechanic told me, "just live with it until it gets bad enough to 'throw a code'". I don't like it, but I've not found any alternatives (can't afford a new one!). Good luck!

 

Well this morning it ran like poop for a while and then finally threw a code. (We swapped #8 and #5 COP yesterday to see if there was any change) COP #5 seems to be bad. Replaced it and so far so good. Time will tell. Thanks again everyone for your help.