Looking for a little help here with my '01 F-150 / 5.4L. Developed a misfire last week and took it to Autozone & had codes read (no CEL at the time). Got a P0307 so I bought a new COP and replaced it. I changed plugs in June so I assumed COP not plug.

Ran great for about 4 days and then yesterday started bucking/misfiring again. I'm going to have codes checked again but does anyone have any ideas? Why would it run good for a couple of days and then redevelop the same issue?

Could a vacuum leak cause this behavior? I'm about to lose my mind trying to figure this out.

Thanks for any help.

 

Pull the COP and look for moisture in the pocket. Possibly a small leak from the heater hose or something? If dry, pull the plug to make sure it looks ok. You might get it scanned again first, could be another cylinder.

 

Update:

Got the code pulled Saturday and was P0305 (misfire #5). This just days after I fixed a P0307 with a new coil on #7. Bought another coil and replaced #5 and reset by disconnecting neg cable on battery for 15 minutes. All is good right now but all was good just after I replaced coil on #7.

Does it make sense getting the same issue on a different coil after 4 days? P0307 was the ONLY code Autozone got last week. All is/was dry in the engine bay. Just doesn't make sense to "jump" to another cylinder just days after fixing #7.

Thanks for the help.

 

This seems to be the normal way they go out, in groups!

 

They are all the same age. Bad things seem to come in 3's ya know

 

Great. One more to go.

Checking acct. minus another $45. I had to replace #8 a year ago so at least #5, #7 & #8 are out of the way. I hope to NEVER see COP's #7 and #8 ever again!

 

I've talked about this in other forums, but the miss may not be the COP itself.

The boot degrades over time, allows moisture in, and develops a misfire. New COP fixes it because it has a new boot, and it's dry.

In terms of environmental abuse, the chance of multiple COPs going out within days (or even weeks) of each other is astronomically high. I'd suspect something else, like moisture.

Did you ever change the plugs to a non-Motorcraft brand? Or did someone else?

 

Plugs are Motorcraft double platinum as I changed them in April myself. As far as moisture, absolutely no moisture was detected at plug changed and none seen now as I have been fighting this issue and changing COPs.

It's running pretty good now (no major misfire as before) but it does seem at times like it's almost slightly misfiring as I accelerate from a stop. Maybe I'm just super-sensitive to the issue now - I don't know.

I'm keeping my fingers crossed but I'll keep the boot only idea in mind should I get a misfire again.