During a cold snap my 97 F1504.6L started running rough, especially around 1500 RPMs. Eventually the Check Engine light came on. Diagnostic showed a cylinder 8 misfire. Had the plugs replaced. No change. I put in a new ignition coil on the cylinder 8 side with no results. I then replaced the cylinder 8 fuel injector with no improvement. Interestingly, the check engine light does not come on anymore but I still have the rough engine. Next I will look at vacuum leaks, perhaps new plug wires and check out the exhaust and cat converter for being plugged or something.
I almost think it could be timing from the computer or perhaps it could be throttle control.

Anybody have ideas?

BTW, my 4x4 truck has 150K miles, Up until now it has been PERFECT with no problems. I have pulled horse trailors, 4 wheeled on rough jeep roads etc. It has been a great truck.

Another note, one of the major auto parts chains gave me the wrong fuel injector and I could not install it due to a size difference on the O-rings. Their cross -ref showed it to be the correct part but physically it looked different, was a shorter length hand slightly different shape. I wonder how many others have had this problem. This cost me several hours.

 

Both of my 99 4.6's required spark plug wires at approx 100K miles. Make sure you installed double platinum plugs and that your plug wires are at least factory equivalent.

 

Thanks for the tip. I replaced the plug wires and it is purring like a kitten now. No more shaking and lots of power.

 

same problem except mine originated from a little offroading... i initially thought the computer got wet. ill try the wires. supper helpfull