I have a 01 f150 w/ a 5.4 and 88K. I bought the truck 6 months ago and replaced the plugs and fuel filter then. It developed a miss last week and popped a ses. Autozone read it out and told me it was a #7 misfire. Bought a new COP for #7 and went home to install. Still ran rough. Went back and bought new plug. Installed plug and problem seemed to be gone after drive around the neighborhood. The next day on my way to work the miss came back. I have since replaced all plugs w/ motorcraft plugs, put all new COP's on, had injectors cleaned, and replaced PCV valve. Checked for a vacuum leak and founfd none. Took to a mechanic who ran on a diagnostic machine, he swapped out a couple of the COP's, read out their resistance, and he gave up. Truck will run without miss when cold, but not for long. The miss comes and goes as I drive, idle, or put a load on it. It won't miss all the time, so I can't pin it down. I have read quite a few posts for misfires and have followed all the suggestions I could find. The truck has popped codes since, but they continue to jump around. Original code called a #7, second code called #8, mechanic got a code once for #4 and once for #1. Any help would be greatly appreciated.

 

You said they changed the COPs around some.

Are you sure the misfire code isnt following that COP?

 

I have changed all the COP's with brand new units from Autozone. The code has jumped around, but didn't follow a COP or plug. What tells the plug when to fire? Is there a sensor that tells what coil when to fire? Maybe, my problem lies there.

 

It's controlled by the computer.

 

I've heard that the computers some times need to be reprogramed. Could that be the issue. What tells the computer what cylinder the engine is firing on?

 

I doubt that your computer is the problem.

Another possibility is your plug wires, but I could be wrong, so I would wait for someone else to jump in and get some advice from them because I dont want to get you chasing around different possibilities and spending alot of money on things that dont need to be done.

 

A lot of things cause misfires, the COPs are only one of them. Many of those things also have other symptoms. A scan tool is a reasonably good way to chase them out.

 

the crankshaft position sensor. this also tells the PCM when a misfire is detacted.

 

where is the crankshaft position sensor located? Do you think this could be my problem since my misfire continues to jump around? Can I clean it or just replace it?

 

I had a mechanic put a scan tool on truck and it first said it had a #4 misfire, but after shutting the truck off and working the #4 misfire with no evident cause, the scan tool called a #1 on the second go around. Twice before this mechanic AUtozone read out a #7 on the first SES and a #8 on the second Ses. The misfire seems to jump around. This would seem to rule out COP's, plugs, and harness, but I'm not sure. What's next?

 

on my way home today, ses light came back on. Stopped in Autozone. There scan tool pulled a #3 misfire code.

 

replaced crank position sensor today. didn't help. any suggestions???????

 

1st off stop throwing parts at it!

You prolly wasted a lot of money on un-needed COPs.

You are running blind without a diagnosis and your mechanic needs to go back to working on carburators.

What you need is a proper diagnosis from someone that has a scan machine not just a simple scan tool. A scan tool is only for code reading NOT for what parts to replace. Once you get a code there are many steps to follow to find what caused the code.

In your case since this problem seems so evasive it might be worth it to take to a stealership and pay the $80 bucks to have a proper diagnosis. Now not all dealers know how to do this. What you tell them is that you don't want it fixed you tell them to tell you what is wrong with it and how they (What proceedure they followed) know what is wrong with it. A real up-to-date modern dealer will have no problem with this. a corrupt old fashioned dealer will say "We can't do that" or "We just know that's what's wrong with it"

Now if I was to hazzard a guess, since you said it runs fine when cold I would start at temp related sensors. Air charge temp, coolant/head temp etc.

I wish you the best of luck-

 

I had a similar problem: changed plugs/wires and ran fine for a week, then developed a miss. Found #8 plug wire had come off the plug; reinstalled boot on plug. 1 week later, developed a miss, found #8 plug boot again off the plug; recrimped terminal and miss has not come back.

Could your problem be the plug boots backing off? I could hear the spark "pop" when the boot had backed off on my truck.

Good luck.
Curt

 

I broke down and took it to the dealer today. They say it is my #3 COP. I guess I got a bad part. I tried swapping all COP's before w/ no luck. Of course the misfire would come and go, so I can't be sure how I missed it. They say they guarantee their work, so if they're wrong, I'll be taking it back. I'll let you guys know how it turns out. Thanks for the inputs.