I've had 4.6L engines misfire because of spark plug wiring. I know, it's been tuned up. I had a 4.6 come in and it missed. It was damp and rainy out. Looked in the engine bay, everything seemed fine. Brand new aftermarket wires. Talked to the Ford techs down the street. Advised to change to Ford wires. Said they've had that same problem with aftermarket wires. Changed wires and miss was eliminated. Just something else to check. Ford Coil pack ignition systems are very touchy with plug wires. Same as the GM DIS systems.

Just some info.

Jimmie
2003 F250SD SB SC XLT 4X4