My 2003 F-150 with 4.6 V8 is running very rough while under strain. Got back from Iraq and took it and had tune-up on it and it ran good then started running rough again and took it back and they changed out the number 4 sensor wire. Few weeks went by and started again. Don't have the money to take back so what do I do? It idles fine and aslong as your running at around 30 and 40 mph runs good you get above that it starts spitting, sputtering and serging.
Truck running rough. on 2003 Ford F-150
Do you know what specific codes were stored or why "number 4 sensor wire" was replaced? Was it an ignition coil that was replaced? The OE Ford scan tool measures actual cylinder misfire count which is usually a bad ignition coil or bad spark plug. The faster an engine runs the more it will "smooth out" that's why at idle or under load you may notice the poor running most.
2 more answers
upgrade air intake and exhaust. could be the engine is not breathing properly. may want to reprogram the engine after also.
may be a little late, but had a similar problem with my '97 and it was a result of having a leak in the collant line hat would spray into the sparkplug well and short out a spark plug. Seemed to only happen at start-up with a warm engine or after truck ran for some time. Fixed leak all was good. Hard to diagnose with the engine warm the coolant would evaporate and everything look fine again.