I have a 2002 F-250 super duty with the 5.4 engine. It misses on one cylinder up to about 2000 rpm then seems fine. If I accelerate hard I can feel it kick in and out. I have had it to two different mechanics who have changed the coil packs, spark plugs and some other things I don't really understand. According to them the computer checks everything to be ok. Both of them advised to drive it for a bit because it might just be a carbon buildup. (I just purchased the truck so I don't know history) I interprete that to mean "I don't know whats wrong". One of the mechanics said he thinks the next move is to put a new computer in. Can anyone suggest things to look at. I trust both these mechanics but it seems they've run into a brick wall. Put suggestions in simple terms because I'm a really good carpenter but not a mechanic at all. Thanks

One more thing. After the first mechanic replace a couple of bad coil packs the computer showed all of them ok. When I took it to the second mechanic his computer showed another coil pack bad. Don't know if that means anything or not.

 

Some code reader cannot read pending codes. A cylinder has to have a bunch of misfires before it will light the CHECK ENGINE LIGHT and throw an actual code, but the truck will throw a pending code.

Do you know if the mechanics replaced the boot when they did the spark plugs and coil packs?

 

I don't know if he did or not. I'll have it back to the mechanic today to get a trailer brake unit installed so I'll ask. Exactly what does that do?

As to the bunch of misfires it appears that the cylinder doesn't fire at all in a certain RPM range. If the truck is in Overdrive and the RPM is at 1500 it really rattles things. Almost like a standard transmission when you're in to high a gear for the rpm. If it didn't clear up at higher rpm I would almost think its a stuck exhaust valve.

 

A stuck exhaust valve would causse backfiring through the exhaust. I doubt that is the problem.

The boot prevents the spark energy from jumping to ground outside of the spark plug and keeps the spark plug and voltage path clean. it sounds like you still have a bad COP causing your misfire.

 

Well, if thats true then it will be the 5th one we've had on. My mechanic is feeling like it has to be the computer. He describes it like this; The computer sends a pule to the COP to tell it when to fire. All the other COP have the pulse but the #2 cylinder does not. He says one wire to the COP is hot and the computer must tell it when to fire but that signal (pulse as he describes it) is not coming through. He has some kind of tool that picks up the pulse.

One other thing. This cylinder had the plug blow out ( I understand thats pretty common) and a helicoil was installed. Could that cause a problem?

Thanks for the help. I think I bought a pretty good truck once this problem is resolved.

 

No, a previous blown plug would not cause problem. A properly installed helicoil or other thread insert repair wouldn't cause this.

Has your mechanic actually verified that this spark plug is firing? Has he run a compression test or a leakdown test to verify if the cylinder is sealing? Has he looked at the spark plug to see if it is running lean or rich? (It could be a bad injector)

 

Also trace the wire harness back for that COP. It may have a bad wire somewhere that is grounding out. I am with Redford, if the mech can confirm the pulse is not only getting up to the wire but all the way to the plug then it might not be getting fuel. That injector may be clogged.

 

Here's what I know. A compression test was done on every cylinder and it checked out fine. The injectors have been checked and seem to be ok. The wire was traced back to the main connector going to the computer and passed a continuity check. All other cylinders were checked for a pulse and checked ok. Cylinder #2 was not getting a pulse. My mechanic say's he can't think of anything else it might be except the computer. He feels he's ruled out all the obvious. I just wanted to check all options before spending the $$ for a new computer. Like I said I'm a good carpenter but a lousy mechanic so I just like some 2nd opinons. Does it sound like a computer issue?

Thanks for the responses. I at least feel like my guy has covered the obvious. He maintained over 100 5.4L for the local police department for several years so I feel like he should really know the engine.

 

I dont know. I'm not saying it can't happen, but a PCM failure like that is pretty rare, bordering on unheard of. I would honestly suspect the wiring first if there is no spark signal at the COP. These computers are very rugged and not prone to failure like the first generation PCM controlled fuel and ignition systems.

 

Thanks I'll check with the mechanic again. I'll let you know what we find. Thanks

 

It sounds like he covered his basics! Before you replace the computer, I would just try a reflash first. Go to the dealer and ask them to reinstall the factory program. It might just by the software not the hardware. But I still think it is a wire problem just havn't found it yet.