My 02 F250, 5.4L, has developed a misfire.

Wednesday afternoon, Dec. 1, I washed the truck and rinsed the engine. It ran fine on a couple of very short trips immediately afterward (<.5 mile). Later that evening, I began a 175-mile trip, and after warm-up, it missed in the first 20 miles or so, then smoothed out. The next two days it ran fine on short trips. Saturday morning, it ran fine at first, then after seven miles or so, it began missing. It's run that way since -- during warm-up, it's fine, but after, it misses.

The check engine light has not come on. I've washed a lot of engines including this one and never had a problem before. Without a traditional distributor or ignition wires, I don't really know where to start. Any suggestions are welcome. Thanks in advance.

 

I think the coil on plug connection may be wet. Or there might be water in the tube to the plug. I had that problem after a heavy rain. It ran fine during the rain and a few days later it started missing. I pulled the C.O.P.'s and blew them out with compressed air.

 

Classic symptoms of water in the spark plug cavity. Sounds like you've been very luccky in the past if this is the first time you've experienced it.

Pull the COP's and blow out the water.

Put dielectric grease on the inside of the boots and around the "umbrella top" of the COP to prevent recurrence.

 

Thanks for the suggestions. Probably a good time to go ahead and replace the plugs as they have at least 110k on them.

 

Very good idea! Many of us suggest replacing the COP boots while you're at it. They live in a pretty harsh environment, and do tend to harden and crack over time.

And I'll climb on the soapbox and repeat: Use a torque wrench! These are aluminum heads and do not take kindly to gorilla tactics.

 

over the last 10 years I've had similar symptoms with 2 different 5.4L. My local shop would always say a coil failed and was a common problem on Fords. Have probably replaced 6 or 7. You mean they only need to be dried out??

 

LOL Yes, most times drying them out will fix it. Add some dyelectric grease.

 

OK - coils, yes - after washing the engine. my '06 is misfiring (flashing check engine light and all) and i didn't wash it. It sat in 0 degree snow and ice for a week - then we warmed up (almost to 50 degrees) then a FAST cool down to the mid 20's overnight - Gotta love Ohio... All without starting it (out of town). I drove it today and barely made it home. If it was a diesel, I'd look at the turbo with all the power I lost. I'm thinking water in the fuel from ice and condensation??? Any other thoughts??

 

Update: I changed 6 of the 8 plugs and cleaned 7 of the 8 coils. I couldn't reach the Nos. 3 and 4 plugs before rain ran me inside, and I haven't had time to get back to them.

The truck ran slightly better for a week or so, and then one day was running normally, and has run fine since. Thanks for the advice.