I have a 2000 F150 4x4 with the 4.6 motor, Late last week I was driving down the road when all of a sudden she statrted to mis bad, in fact so bad I couldnt hit 55mph.
does anyone have any idea whast going on with this? I recently bought a new coil pack, I went through each one but couldnt find the bad one.
Any help would be great.

 

Read your codes. You might have a set or pending code that tewlls you which cylinder(s) may be affected.

If no codes, you will need to use a scan tool (not a basic code reader) to access the MISFIRE COUNT PIDs to see where the problem is developing.

Otherwise, you're left with loading up the shotgun and replacing everything, playing some type of round robin with a known good part, or unplugging one injector or plug at a time to see which one doesn't make the problem worse.

Could easily be a spark plug, also.

Steve

 

Listen to Steve's advise, I've been their done that. A good tool that has mode 6 - the cylinder count/history is the key. I'm not sure if mode 6 is an option on the new scanners, But for what the dealer will soak you for it's not worth taking in and half the time there wrong. I have A TSB from Ford I'll post when I find it that state's 50% of the coils returned to the manufacturer are not defective. The basic OB2 scan will not do it, just make sure you can pull cylinder history from the scanner you use and go from there, I plan on purchasing a scanner myself.

 

If you don't want to buy the scanner at this time, Ford dealership will scan for you - I think they charge an hours labor to do so. Make sure they know what you want and talk to the mechanic if you go this route. If your lucky they might do it for free - lol, real lucky!!