TheBestCollie

Good Morning everyone, I have a 2004 FX4 with the 5.4L 3 valve. It has a Cylinder 5 misfire (Code P0305).

Here's the story:
Bought it off a dealer a month ago. Drove it to Riverside and back into the Central Valley with no major issues. MPG was terrible, was getting only about 11. I removed the plug on cylinder 5 to sample the condition of the plugs and it seemed to be old. I put the old plug back in and fired up the truck and it started running like a paint shaker. Scanner was showing misfire on cylinder 5. Parked it for the week and got all new Motorcraft plugs (it was running Autolites). Installed them and the truck ran smoothly for that weekend. Come to turn it on Monday and it was running like a paint shaker again. Scanner again showed a cylinder 5 misfire. I exchanged the plug and COP with another cylinder and it still tested back to #5. I tested the spark and it was good. I also interchanged the injectors with another cylinder but it still came back with #5 misfire. At this point I'm stumped.

My questions are, how do I check if its the wiring to the injector? Or do you guys have any other ideas? Any help is appreciated

SCORGE

A simple thing, but worth a check. Is the COP connection clean/ in tact?

TheBestCollie

Just checked that and the connection is clean. There's only di-electric grease in there right now.

nrivera04

Move the plug and see if the misfire changes.

TheBestCollie

If you mean moving it into another cylinder, I've already tried that. Misfire stays with #5.

nrivera04

My apologies. I miss that... thought you said you'd just move the COP.

I see youre looking at possible electrical. Have you checked voltage at your connector yet?

TheBestCollie

No I haven't checked the voltage. I don't have an OHM meter. Is there anyway to check if the injector is firing at all any other way?

redfishtd

It is not to be used on connectors or metal parts . Boots are to be changed along with plugs, they go bad all the time . that's the only thing standing between the high voltage( 30000 volts) and the head- 5 inches of it . A pin hole is all a misfire needs . Boots are damaged by heat /age / oil etc . Old grease gets contaminated with dirt etc .
Clean the gel off the coil and get new boots and springs ,napa has them . Just use a dab of dielectric grease on each end of boot . Its purpose is to stop boot from heat seizing to plug and keep moisture out of boot .
Clean all coil connectors with contact cleaner and get corrosion off .
To bring people to earth I always offer to let me put 30,000 volts thru the center of these boots while in their hand . No one has taken the offer yet .
Torque those plugs in to 25-28 foot pounds with a wrench not by feel .
Just for your info there have been many reports of new sp515's bad out of the box .

TheBestCollie

I'll clean them out and put it on bare just for testing purposes then.
About the plugs being bad from factory, wouldn't moving around plugs make the misfire move around with the bad plug?
And now for boots, isn't it the same thing, that a bad one moves around with the misfire?

nrivera04

Find a mechanic friend that will let you borrow a noid light is about the only other way i know of.