Greeting to all!

There are so many misfire threads that it's really tough to search for relevant or common symptoms, so I apologize if this has been covered before.

Here's my story:

2002 Expedition with 5.4 Triton. Very high mileage, close to 250K. It's been a great vehicle.

Plugs and coils were replaced about 20K miiles ago. I had hoped that the new coils and plugs would improve the badly degraded fuel economy, but no such luck. I still can't explain why the mileage has dropped from close to 17 MPG (hwy) to around 11 MPG over the last few years, but I'll chalk it up to a very tired engine. Otherwise it's been running great.

A few days ago it started misfiring at cold start and for the first 10 minutes or so of driving. BlueDriver scanner reported pending code for cylinder #2 misfiire. Sometimes solidified to confirmed code, other times started running right before the misfire count got high enough. Replaced #2 coil and plug. Cleared codes.

The problem, exactly as described above moved to cylinder #3. Yes, I checked and reseated the coil and injector connections.

Possibly unrelated - While fumbling around with in the area, I noticed that the rubber "elbow" for the PCV hose was collapsed. There might have been a vacuum leak leading up to these events. In any event, I obviously created or worsened the leak while doing the work on the coil and plug becasue it got LOUD. I temporarily patched it up and vacuum is good now. Still throwing the #3 misfire code.

Not much to go on, but the coil, injector, and control seem to be right for #2 now, and there were right for #3 until the above operation. I observed this for several days, and the only reported misfire until now was #2.

I'd welcome any ideas or wild theories.

Thanks,

Tom

 

It could be the 2-wire connectors going to the coils. If the contacts are not clean then unplugging them and plugging them back in might scratch the contacts just enough to make better contact for awhile.