2000 F-150, 4.6, 4x4, 5speed, 66,000 miles.

I am trying to diagnose an issue I am having between 1,000 and 2,000 rpm when accelerating. I get a slight misfire / intermittent hesitation around 1,500rmp and in a range a little above and below. Seems to do it hot or cold, and sometimes it is not there at all.

Not so bad in 1st, but very noticeable in 2nd , 4th, and sometimes in 5th. But like I said, sometimes (not so much anymore) it is not there at all. I do not notice anything at all over 2,000rpm and the truck is running really well. It does seem to be idling a little rough, but nothing major or that bothers me.

No CEL on. The plugs are original. I run quality brand gas (no grocery store gas for my rides) and it has a fresh pcv valve, k&n drop in, and fuel fiter.

When the misfire takes place, the RPM’s do not change at all, thus leading me to believe it is NOT the clutch trying to slip. However, I am concerned w/ this feeling b/c all of my autos did this before the torque converter or tranny gave out on them (usually around 185k or so) – so I am paranoid it may be a slight clutch slip. This is my first manual to drive that is actually mine, so I am not too familiar with them.

Any ideas on how I can isolate this problem? Thanks!!

 

Dad's 97 does slip a little, and there IS an RPM jump with the noticed slipping. I would say do the plugs and wires first, before messing with a clutch (PITA on these 4x4s)

Adrianspeeder

 

Put the truck in 5th @ about 45mph, then put the throttle to the floor. If the rpms jump and the truck slow a little, the clutch is slipping. As far as the misfire, do resistance checks on all of the cops. This may or may not show a bad cop. If it doesn't you'll probably need to buy a new cop and musical chairs with it until you find the one thats bad. But I'd say the problem is most likely a plug. Change them out, and let us know what you find.

 

This is probably not the issue in your case, but I felt compelled to suggest it anyway. When injectors get dirty, a common symptom is what feels like a slight miss or stumble when cruising at a steady, low rpm speed. Since yours is happening while accelerating, it's doubtful that it is dirty injectors, but you could always toss in a large bottle of injector cleaner just to see if it makes any difference. Either way, good luck with fixing it.

 

I bet coil number 4 is going bad, just replace it, that will fix your problem.

 

let me guess, #4 is on the back of the engine on the passanger side?

I looked around there for the coolant leak everybody talks about on the forum, but mine was dry as could be..

 

Check your motor and tranny mounts. When the drive train is under stress the engine and tranny need to be anchored. When the mount is defective it will give a little and allow the drive train to twist giving the impression of a little slip. There are springs on the clutch disk that absorb the initial shock of letting the clutch out. They can wear out and cause the same symptom. Mine does the same thing sometimes. When I swapped in the 5.4 I had to change the driver side motor mount because of wear and also the tranny mount. If the clutch is slipping there is nothing you can do short of pulling the tranny and replacing parts. If the mounts check out I would live with it till the clutch gives out.

Regards

JMC

 

PROBLEM SOLVED!

Had the time off work over the holidays and went ahead and changed the sparkplugs on the my 4.6. Took a good 6 hrs to complete (i really took my time as to not screw anything up).

It cured my slight "missfire" and slipping sensation completely. actually my truck has never ran this good or strong between 1200 and 2000 rpm. i never realized how sluggish it was in that range until i made this plug change. truck has 67k on it and it was definately due for a chagne. two of the plugs (cyl #2 and 3) were almost completely fouled out from ash build up, i am figuring the previous owner ran some crappy gas or loaded up on fuel additives some time in the past. the truck does not burn oil so it isn't the valve seats thankfully.

my thanks to the list and all the info.