Whats up guys,

I would like to say thanks first off. I've learned alot from this site. Anyways down to the nitty gritty.

97 e350 with a 5.4 157,000 miles.

Had a horrible miss fire/ hesitation at about 40 mph (it doesn't have a tach but its got 4.10's in the rear) only when in high throttle/ low rpm overdrive conditions and only when warmed up.

I swapped the plugs to NGK platniums and put in a new pcv.

Truck ran great, better milage power and drivability. After about 200 miles the problem came back. The miss can now be felt at most speeds and throttle openings but it is still most noticable at 40 mph and high throttle. Still only when the engine is warmed up. First thing in the morning it runs fine when it is cold.

The truck idles well and the miss isn't noticable at low throttle openings and WOT.

Pulled a plug that I replaced and the ground was white. Not the brownish color i was expecting. This seems to indicate a lean mixture. Should I look in the EGR setup on the truck, where do I start?

The engine light isn't on either. I unplugged the MAF and the problem was still there (worse even). Unplugged the battery for 10 mins, to reset the MAF sensor that I tripped, and it didn't help the problem either.

I'm quite confused b/c it ran so well after the plugs were changed. Why is this missing only when the engine is warm?

Any ideas? Any help is appreciated

 

Do you have twin coil packs or COP (coil on plug)?

If you have wires, how old are the plug wires? If they are originals, they are probably breaking down and need to be replaced.

You might also consider doing a search for "NGK" to see what luck people have had with that brand of plug; Motorcraft seems to give the fewest problems.

Best of luck and keep us posted.

 

I'm confident that NGK's are fine even for this motor. I've heard to stay away from Bosch's, and other cheap plugs.

I have COP's and I now have a sneaking suspicision that one of these is the culprit. I had ruled it out at first because I thought that a malfunctioning COP would through a code but I've heard that the engine light doesn't illuminate all the time for COP failures.

I will further investigate this COP problem and keep you posted.

Any further ideas will certainly be entertained.

Thanks again!

 

Check the plug boots. I replaced them on the 98 at a little over 100,000 miles.I replaced the original plugs and the boots while I was at it due to the labor intensive procedure involved. They were $11.00 each at the dealer but I found them for $4.00+ on the net.
They should seal the spark in and moisture and corrosion out. Be sure to use dielectric grease while you're in there.
Good luck and let us know.