Guys, I've been searching here and the rest of the net for a couple of weeks now about a problem with my 05 f150 5.4.

I have a slightly rough idle and can feel a miss at 1600 to 2000 RPM. Sometimes running about 65 MPH up a slight grade I can slowly press the gas pedal and the engine will begin to miss much worse, causing the truck to shake pretty bad. When it gets this bad it will slowly flash the CEL and I get a P0306 code (Cyl 6 missfire).

The truck has 148000 Miles on it and the plugs were replaced at approx 120000 by the dealer.

In the last week I have replaced the plug in cylinder 6 (looked ok) and have replaced all the COP's along with the fuel filter and the injector on #6.

I haven't been able to get it flash the CEL light or throw a code since replacing the COPs though and I am at a loss at to what to try next.

I have seen a few people have very similar issues but haven't seen where anyone reported back what fixed it.

I'm hoping someone here has some insight for me before I pull the rest of my hair out.

Thanks in advance for any assistance.

 

Sounds like a injector too me

 

After replacing plugs, coils, and injector on the problem cylinder, your next logical step is a compression test.

Also, have you ever replaced the VCT solenoids? They are a known fail point and can induce your symptoms and much worse.

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