Hello everyone, new to the site. Fleet tech on about 130 Fords, and finally have one I can't figure out. We've got a 2006 F150 with a 5.4 in it. One of the new kids was told to change the spark plugs, then when I went to start the truck the next day it was missing bad. Plugged in the Ford IDS, number 7 cylinder is dead. Only codes are for that cylinder misfire, and random miss on startup. So, I double checked the kids work and it was all fine. Tried putting a new plug in, didn't work. Moved the coil to a different cylinder to see if the miss would jump, stayed on number 7. Used a noid light to verify COP harness was working, and it was. Put a new coil on it anyway since I had one, still missing. Used noid light to verify signal going to injector for the cylinder. Signal was good, replaced the injector for the cylinder. Still misfiring. Ran a compression test and the cylinder has good compression. The threads for the plug are fine, not cross threaded or torn out. The only thing I can think is that the PCM has gone bad in a way that its firing the injector/COP, but doing so at the wrong time some how. Every other cylinder is running fine, O2 sensors fine. PCM isn't trimming anything back to account for anything, and if it was it would do it to multiple cylinders to keep the engine balanced. SO, has anyone got any ideas on where to go from here? Cant think of any more tests, and I don't believe there is anyway that the airflow could be restricted to only 1 cylinder, but I could be wrong. Wanna try and solve this to keep from sending it to the dealer. Thanks.

 

I seem to be running into the exact same problem with my 06 5.4, i tightened the spark plugs last night, and after i took it down the road, it was misfiring and running rough. checked all of the coil packs, everything was plugged in and seated properly. I'm going to monkey with it tonight, ill update what i discover (if anything).

 

Well ironically enough, my truck had a cylinder 7 misfire, ended up being a damaged plug. i was going to tell you to check the harness wiring, but you seem to have covered everything. i don't think the PCM can fault in this type of manner though? at least ive never heard of it doing so. wish i could help you

 

Unfortunately I tried replacing the plug without results. We sent the truck to the dealer yesterday, I expect to hear from them by tomorrow. Ill post when I find out

 

Ford dealer just called, turns out the kid that originally changed the plugs dropped something into the plug hole and now we need a new motor. Good thing the fleet is backed by a millionaires bank account, ain't even mad.

 

Yikes. My guess would be that plug broke and he didn't blow it out with compressed air after extraction. Still makes me wonder though why it would be missing with good compression since you checked it? Kind of weird. Most of the time, those pieces usually get blown out of the exhaust valve and get caught in the cat.

 

Definitely a possibility. And for the compression, it spiked good on the gauge, but had a 40% leak down afterwords. The other cylinders had 0. Also using a camera, the tech at the dealer says he looked inside the bore and saw the piston was gouged and scraped.