I have a 2005 f-150 lariat. It sounded like it had a small misfire but it ran good. I took it to an auto parts store codes showed the camshaft position sensor was bad, the number 4 plug and the number 4 ignition coil needed replaced. I replaced all 3 and all of the plugs. After that the engine started running really rough. I couldn't get the truck over 25 mph, sometimes I hit the gas and it wouldn't go at all. I took it back in and they said the number 4 injector was bad. I had that replaced yesterday. The shop said it had low compression on cylinders 2 & 3. I'm confused. It went from running just fine with a small misfire to all of a sudden running like this only after replacing all of the plugs. What could have happened. Please help!

 

so basically you need a new engine. i had a similar issue, low compression. ford wanted 5600$ to fix the valve. mine was from an improperly done helicoil however.

why dont you call them and ask?

did they do a leak down test to determine if it was the rings or intake or exhaust valves?

i would bring it to ford and see what they say.

even with low compression it should do more then 25mph, sounds like you need to run the DTC codes again. its probably in LIMP mode.