Hello I have an 07 F150 5.4 with a #8 misfire. Changed all plugs with motocraft . changed the cop. same issue. misfire from idle to high rpm. changed fuel filter 6 months ago. truck has 225000 km. injector maybe???

 

Anybody got a suggestion????

 

I would absolutely check the injector, there has been documented replacements at all mileage levels. But right now I severely doubt my diagnostic skills.........

 

Move #8 injector to the #5 spot.if the miss moves its the injector if it doesent do a compression check.

 

Will do. I hope its the injector ! Gonna swap it out this weekend. ill let yous know how it goes. thanks

 

So replaced the injector ...same problem. what do u do now??? Guess ill have to take it to ford. I've replaced everything!!

 

Compression test time.

 

If you have access to an oscilloscope, and know how to use one, you should look at the wires going to the injector. One wire should be at 12V, and the other wire will pulse negative. If you don't have access to an oscilloscope, the next thing you can use is a noid light. You can use this same process for looking at the wires going to the COP.

 

Get cats checked too.

 

So compression test was good 150psi . since would a.plugged cat cause one cylinder to act up? I would think it would cause multiple cylinder issues.

 

You are correct, a plugged CAT wouldn't only cause a misfire on #8. Either the injector, or COP isn't getting the proper signals. Do you need any other information from post #8?

 

All i would have is a normal volt meter. u gave a digital and analog . This should work to tell me if i am getting voltage or not to the coil. is this the same for the injector plug?

 

No, because you have to look for pulses. A standard meter can't respond quick enough.

 

True, but he can check for 12V on one side of the injector and COP. Matter of fact, with the ignition in the "RUN" position, he should measure 12V on both terminals of the COP, and injector. Without a negative pulse on the "pulsed" terminal, the 12V should feed through the winding on the COP and injector.

 

Mine were clogged. Only cylinder misfire was #5.