I have a 99 F250 LD 4x4 w/ 5.4L Triton.
While driving down the road today I developed
a really bad skip. The truck starts easily but skips
really bad when under a load. Like just going up
a hill. I think it's probably a problem with a COP.
No check engine light. Any suggestions ?
I can also smell a rich fuel smell . As if there's a
dead cylinder or the FPR is bad. So which is it?
Bad COP or Bad FPR ?

 

is your cel coming on at koeo? I would try to read the codes even if the cel is not on koer

 

That definitely sounds like a bad cop. To find problems in specific cylinders I use to pull each spark plug wire while the truck was running and listen to the engine. If the engine starts running worse and rpms drop that cylinder is working. If there's no change then you've found you problem cylinder. I'm not sure how well this will work with cops or if it can cause damage but the basic concept should work. Be careful though there's a high risk of electrical shock.

 

could be a bad crank sensor too. its purpose is to detect misfire...but then again the PCM would more than likely throw a CEL for the bad sensor

 

you can unplug the coils just like ryan said if it skipping at idle. but if its only doing it going down the road youll need a scanner that has mode 6. that i s a misfire counter pid on most good scanners.

 

Mode 6 is good if you have a scan tool that displays Mode 6. Don't forget Mode 6 data isn't real time. Those are stored misfires. I wouldn't go pulling the secondary wires on a running engine. Better to disconnect the COPS one at a time to see if the RPM drops. You can do the injectors at the same time to see if they are working. You need an assistant to put the vehicle in reverse with foot and E brakes "ON". Have the assistant bring the RPM up to load the motor as you pull the COP and injector connectors. Do only one at a time and move on to the next connector. If the RPM drops and the engine shakes that COP or injector is good. If there is no change that's a fault.

 

If you can get access to a code reader, you'll probably find that you've got a pending code that hasn't tripped the check engine light quite yet......

 

Thanks for the suggestions guys. The weather is going to
be warmer Sat. so I'll get someone to put the truck under
load while I pull connectors.
Still no codes though. I can't believe it as bad as it shudder's under acceleration. Mild acceleration on a flat
road isn't to bad but once you start up a hill, Damn!
I'll post again once resolved.

 

Pulling coil plugs with the specific condition presented won't find a bad coil.
This condition is a coil with shorted turns causing low output not total failure.
It usually shows up in OD lite load conditions when the EGR is open, the fuel is cut back and ignition is advanced.
These conditions present the coil with a very lean mixture that is harder to fire the spark plug so an intermittant missfire occurrs.
Since the problem is not a hard fault, no code gets set.
The PCM does see the fault but resets the temporary fault storage memory as soon as the fault clears by a change in the engine load conditions, until it happens again.
Finding the coil by stress testing or subbing one at a time until the condition cleans hoping the replacment coil is good and there is not more than one to cause confusion.

 

could you have your scanner with you or if you had a scan gauge and driveup a steep hill causing the issue while you check the scangauge or pull over and try and read the pending codes

 

Turns out it was the #4 COP.
Luckily it did show up by pulling COP connectors while
the truck was in reverse and idling. I could detect a slight
change in rpms as I unplugged each coil. There was no change in #4. I only changed that particular COP but plan
on a complete change out of all plugs and the other 7 when
it warms up some. lol... I purchased the truck used and I can
tell that neither the plugs or cops have ever been changed and the truck has 201,000 miles. Thanks for all the help.

 

Not sure if you checked it, but it could be the plug too.

 

thats why i said he would need to find one with mode six
if he goes in to mode 6 it will show his misfire

glade you got it fixed

 

#4 cylinder is notorious for going out due to water/coolant leaking into the cop/spark plug hole. May want to check it so you don't have to buy another cop.