well here goes, used to hang on the superduty forum, but made it on down here when problems arose with my 5.4 and found a whole lot of info. Posts by Loudist and LxMan1 really helped point me in the right direction, although I have yet to find the cause of the skipping in my motor.
Problem description, a skip or misfire which isn't really noticeable until the vehicle warms up. barely noticeable at idle, most noticeable from idle to about 2500 rpm especially when loading the engine. If you floor it, it seems to go away but thats about it, and when the vehicle is coasting on level ground without loading the engine it is also gone.
The truck is a 2002 F250 4X4 Super Cab XLT with Auto trans. I have done regular maint on this truck per mfg specs. This is the only problem I have had with this truck and it is kicking my butt. I have my own OBD scanner and the truck is throwing no codes at all.
This is what I have done so far.1) Changed plugs(motorcraft) and checked COP resistance value while out. Had five read .8 ohms, two read.9 ohms, and one read .7 - Given values on here were .5 to 1.5 so they all look good, reassembles and no change. Plugs had 52,000 miles and looked good but changed anyway
2) changed fuel filter- did nothing
3)changed IAC valve- did nothing
4) cleaned MAF sensor- did nothing
5) changed air filter- did nothing

again, the truck throws no codes and checked between each step for codes. My local dealer who I bought my parts from, says he can do a dianostic check of the vehicle for 69 bucks that he says will find the problem for sure. He thinks I have a weak COP that is dropping out under load, and the only way to tell is with a "balanced load test" whatever that is, but for seventy bucks, I am ready to pay. Any ideas????? Thanks, glmf

 

A power balance under load would probably be the best way to find out which cylinder is misfiring. Your dealer will hook up their WDS scan tool and go for a roadtest. A misfiring cylinder usually shows up easily.

 

Thank you sir, at this point, I really have no other options. Hope it goes like you say and that is the problem, thanks again

 

Unfortunately, at this point, $69 is probably going to be money well spent. They have a high-tech scanner that can monitor all of the engine functions while driving the vehicle and the miss should show up then. The way I look at it, It's better than throwing more parts at it and not fixing the real problem.

Jimmy

I guess I sound like an echo of Dave, since I started reading this thread and had to walk away for a bit. I came back and replied without refreshing the page. Oh well, 2 heads are better than one I guess

 

Yes, thats the way I figure it. Consider myself to be very mechanical, but don't know modern EFI car engines at all. So this foray has enlightened my condsiderably. Also did a fuel system pressure test with a cheap tester I got at Autozone. So I do feel more comfortable with my understanding of the engine, and the plugs weren't really too bad at all. Still would rather work on my snowmobile or atv/boat engines though! Thanks guys

 

Let us know what you find out.

 

Well guys, drove the truck one hundred or so miles today and not a skip of anykind, of course I have an appt. at the dealer on Monday for the balanced load test, think I should keep the appt. if the truck isn't acting up??????

 

It wouldn't hurt to have it checked anyway.