When this started the Navigator just died while my wife was driving at 25 mph and it wouldn't restart! When I got to it found a 30 amp fuse out! Can't remember the fuse number (I think it was 19) but if you are looking at the fuse block under the dash cover and looking at the fuses it is the one on the bottom left that was out! I replaced it (unfortunately had only a 25 amp) it started and on came on the SES (Service Engine Soon) light. Scanned and found the P0306!
OBDII code P0306, I know that it's a misfire in cylinder 6! Replaced coil, spark plug and it comes back! Tried swapping coil, plug and fuel injector with different cylinder and still P0306! Performed compression test and leakdown and both perfect!!! Trying to diagnose backwards and can't figure it out! I don't have a manual on this vehicle and am trying to ascertain the electronics! BTW you can feel the misfire!
So thats my story, has anyone got an idea? Unfortunately had to take it to the $tealer since they were the closest shop, and they don't know yet either, but are trying to say it may be a problem with the head and will have to be replaced, but they sound more like they are guessing at this point! I have a hard time with that when compression and leak down are perfect. Does this beast have a central control module or ???? It sure is striking me as electrical and not mechanical!
Any and all help is greatly appreciated! I've posting this in multiple places on this forum, since being new I am not sure where the best spot to post would be!
I have heard that if DIS coils ground out, it can distroy the coil driver in the ECM. I can't remember where I read that or if it was even ford COP related. Sence you have replaced the coil/spark plug on that cylinder, check the wiring and suspect the ECM.
Something else to check on, if you used any neverseaze, was it the non-conductive variety? Your issue could be as simple a bad ground to spark plug.
Thanks for the information! I agree, something with the electrical system caused the issue and continues to be the issue! With all the details, I have a very hard time believing that the mechanical aspect of the head could our would cause this problem!
I did mention that to the $tealer when they called me yesterday to advise that head replacement is over $5k an would just suggest a long block for over $8k! They are supposed to be tracing that down but I haven't heard back yet! If they don't have a valid repair plan this morning, I'm having them reinstall the original bad coil and I'll bring it home and start tracing everything by hand!
Thanks again and if you think of anything else, please let me know!
Just got a call after bitching the $tealer out yesterday about it being a short and not mechanical and guess what!
They found a wire to the injector was shorted out! Tried to sell me a complete wiring harness for over $1k installed and I said no, button it up and I'll fix it! A couple minutes later they came back and said oh, we can fix the wire we don't need to replace the harness!
Damn $tealer's, I don't care what I have to do, I'll not go back there again!!!
I came across this forum while banging my head into a wall because of a repeat P0306 on a 2001 Lincoln Navigator (5.4L, 4x4- 120k miles).
I replaced the plugs, coils, used seafoam and lucas oil treatment, checked all wires, still no go.
Every single time I replace either plug or coil on cylinder 6, the problem goes way for about 1 week / 200 miles. The car runs fine, accelerates strong; in other words, I cannot "feel" or hear a misfire.
I reset the code, and comes back after 5-10 minutes.... I am starting to think this might be mechanical.... however, I do not understand why it works fine for about a week after I replace coil/plugs? I tried moving plug/coil to other cylinder (7) to see if the problem moves as well - no dice.
I am getting desperate here, any help is greatly appreciated.
Bottom line: if this is mechanical (nightmare) wouldn't I see that nasty 0306 within minutes after installing a new plug or coil? I cannot wrap my mind around this one: why does it drive perfect (starts with 1 crank) for a week before it starts doing the damn 0306 code?
Did you ever find a solution? If so, what might it have been? My 2000 Excursion XLT (320k miles) perceptibly misses as some highway speeds. I have a ScanGaugeII that displays P0306 and P0000. I don't have an extra $8k, $5k, $1K or any other of those quotes for dealer repairs. I'm in the $50-100 range.