I need some help. I own a 2004 5.4L 3V with 119,000 miles that has developed a mis in cylinder 1. The miss is only intermitent and only at idle while in drive, always at a red light. The pending code is P0351. After I got the code the first time, I changed the COP. A week later the mis came back. This time I had a code for the COP and an o2 sensor stuck lean. I erased the codes to see if it would come back, but the only p0351 came back. My next step was to take it to the dealership and they said it was the fuel injector leaking. They replaced it as well as the plug on that cylinder ( I had already changed the plugs at ~95,000). That was 2 days ago, and today the mis came back. The light was not on, but has a pending code of p0351. Can anyone give advise on what could be the problem? Thanks for the help.

 

Perhaps a bad harness on the COP? Those clips break real easy and can cause the harness to not seat real well.

 

Thanks for the tip. I checked today and the clip looks OK I think. It doesn't look broke or loose. Could it be a bad wire going to the COP and how could I check that? I have had a few people say that the problem is an o2 sensor. Would that cause a misfire in only one cylinder and the same one every time?

 

I can't see how an O2 sensor would give a misfire code. If you replaced the COP on that cylinder and are still getting the same code, I would scrutinize the harness and wiring for corrosion, cracks and splits. You might also consider removing the COP, pulling the boot and checking it as well.

 

I will try looking tomorrow. Do you have any suggestions how to look at the wires that are bundled together? Or do you mean just the ends where the connections are? Also, do you know where the wires go to so I can check the other end? Sorry for so many questions, but I am new to the COP. I am used to plug wires and a single coil.

 

Well, you can pretty much just look at the wire coming out of the bundled loom to the COP. It's next to impossible to check to the wiring once it's interfaces with the loom wires because they're all bundled together. All you can do is look for cracking at the harness and the few inches of wiring before it bundles with all the other wires from the other COPs and injectors. It could also be you just got another bad COP. Its rare but does happen. If all the wiring and harness looks good you might consider getting another COP at Autozone or Orielly's. It's another $20 or $30, but it might solve the problem. Don't forget the dielectric grease as well. Problems like these are like gremlins and out of frustration others have gone to the extreme to replace all plugs, COPs and injectors to rid themselves of the problem.

 

Run a compression check on the cylinder in question. I had a misfire code because of a valve not seating properly and it took a new head to resolve the issue.

 

That's the news I didn't want to hear. I have it back at the shop and they can't seem to find anything wrong. I was even told once they cleared the code that it hasn't misfired for them again.

 

Well, I hope not for your sake: It could be costly!
Mine did not throw a code at first, and it only seemed as if it had a rough idle like a possible misfire due to maybe bad gas or maybe like a wet plug wire (occasionally). I also used a "tune" and I kicked up the idle a bit, to about 760 or so, which helped mask the rough idle. It became more noticeable as I started to look for it and when I started getting codes, it was a misfire at low rpm on #8, (P0308 I think) the cylinder that this valve seal in the guide wore which allowed the valve to not seat properly, at a slight angle, hence a small drop in compression.
First dealer did not discover the issue, just told me no compression and that I needed a new motor: at a cost of $6300 and change...
Second dealer asked to open the valve cover to see if it was a broken valve spring, then asked to go another step, and pull the head. That is when the problem was found. I was thank full that my Certified Pre Owned Warranty cover the head replacement.
Best of Luck: keep us posted.

 

I had an Expy that did that same thing. Replaced the COP and plug on the dead cylinder without any help. Took it to my dealer (who is great about runnning diagnostics @ N/C) and it was the ground side going back to the PCM from the COP. It had fire going to the COP but nothing in the return circuit. The mechanic found the wire and spliced in a new piece rather that tracing all through the harness. Over the next 6 months or so, it did it on 3 of the 4 cylinders on the pass. side bank.

 

Ok. I got the truck back yesterday. So far it seems to be doing fine, but time will tell. They said that when the coil was put back on, probably after the injector and plug change, that one of prongs inside of the clip that goes on the COP had actually been pushed back into the clip. This was leading to a bad connection. They even fixed it at no charge since they changed out the injector and plug. I hope this fixes the problem and thanks to all that have given advice. I will keep you posted in the future if this works or not.

 

It's back. I was at a redlight yesterday and the mis started. This only happens while at a stop while in drive. It goes away after I pull out and get to about 10mph then it runs good. The pending code p0351 is the same as it has always been. Does anyone have any more suggestions? I am thinking about taking it back to the dealership and ask if they can replace the one wire.

 

Big, if you get this figured out, please post it here on this thread because I have same truck as you and same problem. It does seem to do it worse when at a redlite and an uphill incline. Started doing it in June and still does it occasionally this winter.

 

This all sounds familiar. Flashing CEL...mis-fire on Cyl 1. They replaced COP. Said it was good to go. Drove 2 blocks, light is back flashing. They replace injecter. Well, that did not work, still running rough. Said compression is 70 PSI, should be 160 or so. They gave up and said take it to Ford dealer. Any thoughts that can make me feel better ?

 

I had this problem: I replaced plugs and checked cops etc... First dealer said I needed a new motor, at about $6300... The 2nd dealership confirmed low compression and ask to remove the valve cover to look for a broken valve spring: upon not finding anything they asked to go one step deeper and remove the head. I said yes and when they did that found a valve not seating correctly causing the low compression. I have a new head installed at about 50,000 miles, and its been about 14 months and she still runs good.
Good Luck!