Ok I'm working on a 1997 ford f250 with a 5.4 in it.It runs ok but when you level out in town about 35 or 40 then step back down on it to keep the speed it bucks.If you really get into it it runs great. but when you try to just drive normal in town it bucks.Anyone have this happen and what did you do to fix it.Any help would be great.
ART

 

You have one bad coil that won't set a code because it is not a hard fault.
Don't wait for a code to tell you what cylinder or you will wait a long time.
Get one new coil and change swap one cylinder at a time until you hit the bad one.
The bad one has shorted turns but still works is why it's not a hard fault.
Resistance check is usually meaningless on this issue.
Good luck.
KM3F

 

Thanks for the info.I'll give it a try.
ART

 

Since the truck is a '97, he doesn't have COP's. He has one coil pack on each cylinder head, and sparkplug wires.

How many miles are on the truck? And have the plugs & wires ever been changed? Could be a bad wire, plug, or coil pack...

 

It is a 97 but it has cop.It was made 11/9/06.It has around 18500 on it.
ART

 

It absolutely has COP's and that is almost assuredly what is wrong. Had the same thing happen but the CEL came on within a day or two to tell me which cylinder it was.

FYI 5.4L's NEVER came with coil packs.

 

I just changed the coil on the rear cyl. on the right.Fixed it right up runs great.Thanks for the info.
ART

 

If you mean by "right" as in from the drivers seat, you may want to check that heater hose in the engine bay. Those have been known to leak antifreeze and drip into the #4 plug hole, causing a misfire.

 

Good to hear you got it that fast.
To finish out what the whole issue is, at low speeds and light throttle the fuel is cut back making the mix lean then add to that the EGR opens to advance the spark timing.
What you end up with is a very lean mixture including the exhaust gas being fed back into the intake.
This requires higher spark voltage that is the reserve the system is supposed to have.
With one coil that has shorted turns it's voltage is down and unable to fire it's cylinder so you percieve it as a miss.
Since it is temporary in nature, and clears as soon as you give a lot of throttle to force a change in operating conditions, the voltage requirements come down to the point the bad coil is able to fire it's cylinder again.
Thus no code is set to tell what cylinder is the cause without tracking it down by either subbing or a dealer stress test of all the coils until the low output one is found.
A lot of shops still have not caught on to this yet.
Good luck.