When I am going around 45 to 60 MPH whenever I press the gas pedal you have to press hard. If you just lightly press it the engine jerks and hesitates like it jumping gears. Dealer claims it is bad plug but it has been changed 4 times new coil pack, fuel filter, o2 sensor on bank one. Fuel injector has crossed my mind but why does it not affect it when it travels over 70 mph? Any help would be great I am lost.

 

Year, engine, type of plugs that were used, etc will help us get a better feel on the problem.

 

I forgot to mention that part.
It is a 2004 5.4 4x4 XLT. The plugs were Motorcraft and the coilpack came from a Ford dealer as well. The one from Advance Auto was a joke.

 

If it is the same cylinder each time, swap out the injector with another cylinder and check the compression in that cylinder. If the misfire is on that side but keeps moving, get the cats on that bank looked at.

 

^x2. if same cylinder is giving the problem after all that stuff, i'd say injector is next. But apparently you aren't going to a very good dealer if they are just guessing with stuff like that. They can plug right in with their laptop, drive it, and see exactly which coil or injector is causing the trouble.

 

It is always the number 1 cylinder that gives me the trouble. I have been told it is a cracked spark plug. Possible vacuum leak, just running lean on bank one. Got tired of being jerked by dealer I bought it from. Went to another dealer and they want another 90 dollars just to hook it to their computer. quoting service man here " since you have done all the other things I am guessing it is a fuel injector." ok but it only does it in the 45 to 55 mph range when you press the gas. also when it shifts into 4th when you are just traveling down level road it drops from 2000 rpms to 1200 rpms, is this normal? I also installed a gforce chip and no increase in rpms. I am beginning to think this thing is cursed.

 

REMOVE the G-force "chip" open it up and you'll find a $.01 resistor you could buy at Radio shack. It messes with the MAF and causes faulty readings.

 

I have a 2004 f-150 5.4L Lariat. Does anyone know if the pcv valve distributes evenly to all cylinders if i wanted to add seafoam cleaner

 

When was the last time your fuel filter was changed? That $10 goes a long way and it is an easy fix. I would say it is the foolproof way to isolate a bad injector. Might not cure your problem, but it seems like your Ford dealer is taking a stab in the dark as well.

 

Well I changed the injector on the #1 cylinder that always gave bad signal. Still ran bad.... So I take it apart again and see if "swaping" injectors would make a difference. Low and behold the third injector back when it was pulled out the bottom O ring stuck in the injector frame. It was plain nasty. So I clean the injector pull the O ring out and put it back where it goes. It alot better when I drove it a few miles...I will findout in the AM if that takes care of the misfiring for now. Thanks to everyone for helping. It did kinda suck paying 142. for the injector from dealership.