flockoshot

2012 F150 5.0. I have a worsening misfire P0308 (Cylinder 8) and occasionally a P0300 (Random/Multiple Cylinder). First thing I did was maintenance, replaced all 8 plugs with Motorcraft and set the gaps at 0.045. I drove about 100 miles and pulled the #1 and #8 plugs out to inspect, also because I wanted to swap the coils from #8 to #1 to see if the misfire follows. I will find that out tomorrow if it does, but I did notice that the #8 plug has considerable yellowing on the porcelain insulator nose, while the #1 looks pretty clean compared. I attached the picture. Does the yellowing on that plug point me in the direction of my possible misfire problem from #8 cylinder? What else should I check out? I plan to get a compression gauge if I can't track down the problem. I'm hoping it's an injector or a bad COP, but my luck it's probably much more serious. I used compressed air to blow out the electrical connectors at the COP, but it's hard to tell if it's dry because there is dielectic grease on them. Also of note, I paid my Ford dealership a pretty penny to perform the TSB # 15-0126 PCM update and also reset the cam and misfire calibration with the scan tool, but that didn't cure my misfire, in fact is may have made it worse. I'll update tomorrow what swapping the COPs do, but I'm not optimistic that it'll follow.

#1 plug on the left and #8 plug on the right... driven 100 miles since replaced. Does the yellowing mean anything concerning my misfire?

PerryB

I'm leaning toward an injector, but you're on the right track with your diagnostic procedure .

flockoshot

I sure wouldn't be sad if it was an injector. I couldn't find a thread explaining the procedure for removal, just assuming it's pretty straight forward. I just never know about removing some of those clips and such without damaging or breaking them. I find a special tool is sometimes required. Fuel under pressure can get messy.

flockoshot

After a 10 mile drive this morning, code reader is indicating a pending P0308, so looks like I can rule out the COP.

PerryB

If the 5.0 injectors are like the 5.4, the clips come off easily. Yes it does spew some gas, so be careful and have the area packed with rags. When you reinstall the injectors and rails, give the O-rings a film of oil or dielectric.

FLXLT

There have been issues with cylinder 8 misfires as a result from overheating in that cylinder. Think it's more common in Mustangs or tuned trucks but just something to think about.

Hoping it's just a bad injector.

flockoshot

I did read some on the other cylinder 8 misfires, including the overheating. No tune, though.

Does the pressure need relieved in the rail before I remove it?