This is my first post. These forums are unbelievable. I just purchased a 2004 F150 S-crew Lariat. It has a serious miss under any load (especially hills). It came from a car auction with the motor in pieces. Apparently it got reposed while at a dealership getting repaired. I put it all back together and it runs good, but not quite right. Like I said, under load it misses bad, especially after it warms up good. I found many good threads on here with the same problem so I began to try to diagnose the problem on my own. I replaced the fuel filter. I checked the fuel pressure, it was good. I borrowed 4 coils from a company truck where I work and changed the front four to see if that was it. Nothing. Didn't try the back four because of difficulty getting to them. I finally gave up and took it to the The dealership. The mechanic hooked it up to the computer and we drove it. It was missing on all eight cylinders. He said he had never seen one do this. It feels like an ignition problem. He wants to replace the plugs. He said he found a TSB saying it had to have a specific numbered plug which it did not have. I am afraid he is going to just start replacing parts until he gets it right and that will cost me. I have read many things on this forum such as grounded wiring harness to injectors, bad injectors, bad coils or boots, etc. I was wondering if anyone that has had this problem and ever got it fixed.

 

Plugs could do it, the 3v plugs have a long section after the threads before you get to the electrodes. Depending on the mileage it may not be a bad place to start. The mechanic's scan tool should test injectors to show shorts and possibly duty, so he should be able to see if one is sticking open or not working as much as the rest.

 

Plugs seem to have done the trick for now. It is 100% better. It still has a little issue. It has one exhaust lifter ticking. I think it may be setting off the knock sensor and retarding the timing. I will change that lifter next week and see how she does. Thanks for the reply.