2006 5.4L Intermittent Dead Miss

[bskouby]

Well...I may have made some progress on this issue. Yesterday I pulled the COPs and spark plugs. I was thinking if I was suffering an actual misfire, I should be able to see some evidence on the plugs. Seven of the eight plugs all looked good. Just a bit of carbon buildup on the shanks, porcelain insulators, electrode, and ground strap all looked good.

The plug in question was from cylinder 5. I noticed that when I pulled the plug it was not as tight as the rest. It is possible I didn't get it torqued down all the way when I replaced plugs 5000 miles ago.

Anyway, the shank was completely covered in carbon build up, in fact there was even carbon on the seat of the plug all the way up to the first threads. So, that can't be good. That aside, the electrode and porcelain looked good. I cleaned the plug in question and put it back in the same cylinder with the same COP.

I also noticed that my battery need to be replaced. The little green window was no longer green, the dreaded red ball had made an appearance. I have been keeping an eye on this for a few weeks, I noticed that the battery had seemed a bit weak on start-up.

With cleaned and re-torqued plugs, reseated COPs, and a new battery the truck is running great on the custom tune. Maybe between the iffy plug and weak battery it was enough to cause a misfire when pushed.

I don't know if the problem will come back, but I figure I found enough things to fix on the truck to make a difference. The jury is still out, but it is looking good so far.