guys, posted this on the 5.4 forum, maybe someone here can help????well here goes, .
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

 

Does your obdII scanner have capture mode ?
if it does it will capture misfires /cyl. and point you in the direction of the bad cop. when you had the cop out did you notice any burn or cracks in the boots?
its common for the boots to crack and misfire.
a far fetched idea is a bad injector or loose connection to it

Rich

 

Don't know if my scanner has capture mode, will check that in the AM. Didn't notice any tracks or burning on the COP's. But on reassemble, put the back COP's on the front plugs and got misfire on #5 cyl, which originally was on #8. Checked it out again, and found nothing wrong, put back together and no more code. So maybe this is the culprit and showed its ugly head for a minute or two. If my scanner has capture mode, can I drive the vehicle and see if it produces the code????

 

My V10 had this problem a couple weeks ago. I had one bad coil and another intermittant one. I used my OBD software to tell me which ones. It hadn't thrown any codes but I did a test and it told me misfires for each cylinder.

 

Your Coils are spiking - one or maybe two are bad. One is worse than the other, causing the spike.

I don't know how much they charge in your neck of the woods, but here a Ford tech charges $75 per hour (or so) and it only takes about 30 minutes to find it. They use a WDS (world-wide diagnostic system) during a Driveability Test. I had to hook to a heavy trailer in order for them to find the bad coil, but I have the V10

Hope this helps - let us know.

 

Could the cause of this problem also be tied to mine? While cruising along at a slower speed (30-40mph roughly) with a steady pedal (ie, no acceleration or deceleration), my engine will rev up a bit. Is this the coil thing as described above? or am I between gears and the automatic OD tranny can't decide which gear I should be in?

Thanks!
Daryl

 

I think its the trasmission hunting, mine does the same thing.

 

Well guys, drove the truck today for about one hundred miles and not a single skip, ran perfectly. Dealer can't get me in until monday for the balanced load test, and am not sure if they can tell what the problem is if the truck isn't acting up. Any ideas on if I should still let them test???

 

One more thing, to Stan Wright, if your truck threw no codes, how could the scanner tell you which cylinders were the bad ones????? This truck has shown no codes whatsoever during this whole dilema. Except when I got all the plugs changed, and fired the truck, it seemed worse with a noise on the AM radio, scanned and it showed a misfire on #5 cyl. I had moved the back coils to the front of the motor just cause I heard the back ones always go first. Anyway, pulled #5 coil and found nothing out of the ordinary, put it back together and idle fine, just with the original problem only and no idicated misfire on #5,,,,don't know what that was all about but maybe this coil is bad and for the short while was causing the indicated misfire?????

 

did you use a good amount of dielectric grease, I've been told this can cause random mis-fires

 

My v-10 has done the same thing a couple of times since I've owned it(about 75,000mi) and whats wierd is I would let it sit till the next day and it would run fine. Well I broke down and spent the 30 bucks on coil boots at NAPA and it hasn't done it since now. I changed the boots and put some dielectric grease and blew the holes out at 100,000. And I now have 102,000 on it with all origional coils and it runs great. I think that sometimes it was damp enough outside that maybe some moisture would get in the plug hole causing the old boots to arch and I'd get the same symptoms as glmf 1 is describing. just my $.02, good luck

 

I have the OBDII software that is ran from my laptop. I can't remember the name (I've only used it the one time)(Pepper?). It didn't show any codes, but I ran a scan test (?). It showed a few hundred misfires on cylinder 6 and thousands on cylinder 5. When I changed the coil on cylinder 5 it appeared antifreeze had been leaking from a connection above it and had soaked the coil. The truck ran great after I changed the two coils. Neither boot looked damaged.

I would have thought that thousands of misfires on cylinder 5 would have thrown a code, but it didn't.

 

For misfires to throw a code ,the pcm has to reach its threshold level which is a very large hexidecimal # .I forget what it is but its very large !

random misfires will not cause a code unless above happens.

Rich