Hey all,

I have a heistation/misfire problem I finally solvedon my 2006 Expedition, 5.4, with 66,000 miles. It was a frustrating process, so I figured I'd document it in case somebody along the line can get some use out of it.

Started out with a hesitation about six weeks ago under load. Nothing major, happened about 3500 rpm on a freeway on-ramp. I changed the air filter and didn't think much about it.

It came back maybe 3 weeks ago under similar conditions. No MIL mind you, but I could tell something was up. Found the biggest hill in my area and decided to push it a bit to see if I could get a code. I found I had to really push it and hold it to get the code to come up. Finally got one, P0306. Took off the COP, re-greased, put it back. No difference in performance, this time got P0300, P0302, P0304, and P0306. Huh? Changed fuel filter, no improvement.

<O</OI then took off all the COPs and checked and regreased them, and put them back. No difference, still hesitated (not bad mind you, but I couldn't get a code). Purchased 8 new COPs on Ebay and installed. Ran terrible!! Put back OEM COP and drove. This time was able to get P0301.<O

Took to dealer, who diagnosed bad COP and plug on #1, which they replaced. Picked up and drove truck, and noticed only marginal improvement. Brought back to dealer. Dealer couldn't find anything wrong, so I went to dealer and test drove with them. Under the exact circumstances I told them when I brought it in both times, I was able to get a P0302 code to flash (within 3 minutes, which tech sitting next to me).

Dealer diagnosed bad COP and plug on #3 and #6, which they replaced. I picked up truck and noticed it was better, but not perfect. I replaced #2 and #5 COP myself with 8 from Ebay to start eliminating other COP, and truck ran worse (I got a PO305, and then a P0302 code)! I put back OEM COP and truck was better but not perfect. I set those two COP aside and put another one of the 8 Ebay coils into #7. Truck ran the same (Ok, but not perfect). Took OEM coil I removed from #7 and put it into #8, and presto! The power seems to be consistent through the whole RPM range now, especially from 3000 to 4000 rpm where it struggled before. Seems to have done the trick.<O
<O
I think I was thrown off by what appears to be a bad lot of Ebay COP. I'm not sure which vendor I purchased them from, but they were 80-something dollars before shipping (close to an even 100 after shipping). It appears there are at least two that are marginal, if not bad. The combination of multiple bad COPs also made it tough to fix, I think. The key in the end was just to try to get it to run at least a little bit better which each COP change and work my way up from there.<O
<O
I hope this helps somebody in the end! It drove me crazy for three weeks. If you are not going to change all 8 (or if you do and that doesn't make it any better!), the key is to get the code. I found success when I could push the truck up a hill or under a load starting at about 40 mph. I wouldn't floor it, but I'd try to get the rpms into the 3000-range. Taking the truck off of overdrive helped out a lot. I'd have to hold it even when it started to misfire, sometimes for 5-6 seconds, in order to get the MIL code. And that didn't always work either.<O

 

Great post thanks for taking the time to write it down.

Having the same issue with 2006 Nav and suspected COP but a few details you have mentioned are exact so now am pretty certain (no codes though but have not pushed for them as you note). Will order a complete name brand set...

 

Hello just to update the misfire ended up being spark plugs. We bought the 5.4 Navigator and didn't get a record for when plugs were changed last, they weren't.

<o></o>
138000 KM's/~90,000 miles on original plugs.

We filled up at Safeway (87 Octane) when they dropped their gas prices and paid for it when the engine misfired during all acceleration. On 91 Octane (Chevron, Shell, Esso), it would only misfire around 50 MPH and you could get used to working the gas pedal to avoid it but with cheap gas it really misfired.<o></o>
<o></o>
Now with new SP515 pugs it ran great even on the cheap Safeway gas but will use name brand fuel from now on.<o></o>
<o></o>
Dealer quoted $360 - $450 depending on how many original plugs broke, none broke so was $360 installed. Original coils still working fine.<o></o>