I have a 2003 5.4 f150 fx4 I have been having miss firing problems for over a year now. I have been to a auto parts store to get them to pull a code off my truck and it says I have multi miss fires and miss fires out of cylinder number 6 but I replaced the coil pack for #6 & #7 a week ago and the spark plugs have been changed recently. #6 and #7 have been the only cylinders that have been giving me trouble. I have replaced coil packs and spark plugs more than once. I have yet to find anybody with answers so will someone please give me one.

 

FWIW: My 97 4.6L has been intermittently stumbling and missing and throwing a P0308 code, misfire on cylinder #8. The truck runs well for a few days, then starts crapping out. I wiggle the injector connector and the thing smooths out....anyway, look at the injectors as a possible source of the misfire troubles you have.

 

Look at the injector harness as he said can be one issue as well as the injector itself.

There is a test but requires a pro level scanner from what I've been told. They say go to a Mode 6 data and the vehicle will show what cylinders are missing. Sometimes one will miss but it will blame another cylinder.

Also how is the plug looking? there are sites on how to read a plug to help

 

Good morning and wish timing was different. My go to guy for these engines is on a 2 month commitment elsewhere, so I'm going to ask a couple questions. Any coolant loss? Thinking head gasket. Have you taken a compression reading? And then also when doing the work with the plugs and COP have you used the dielectric grease on assembly. Thinking moisture. Am not going to give the members name over the open forum, send me a PM and I'll see if he has the opportunity to assist. Just respecting his privacy.

 

I have not noticed any loss of coolant here lately, we have not done a compresion test yet, and I didn't think about using dieletric grease I will try that.

 

I have played with the injectors and theres no change in the perfomance. I have double platinum plugs but I am going to change them to regular plugs today to see if that helps.

 

I played with the injectors while the truck is running but theres no change in the tone and vibrations of the truck. its throwing a po300 and po306.

 

Check out Kattumurans post yesterday in the engines section. Something about the coils firing two cylinders at the same time. All new to me, am waiting for an answer.

 

check the boots on the coils also i had a misfire and it was a bad boot they can be pulled right off the coil and its recommended to replace them whenever you replace the plugs and there pretty cheap

 

my truck has been missing really, really bad lately, and i had the po300 code come up on the scanner for my triton 5.4. i have replaced a few of the coils, but never the plugs. why i didnt replace the plugs when i replaced the coils? who knows?!!! anyway, i just got done replacing all the plugs, which had 210,000 on them!!!, and the thing runs perfect. my old plugs were really white though. my next problem is why is it running so lean?