98 F150 4x4.. 4.6 V8

Ok guys question. I bought my f150 a year ago. I have always had some piston slap never has gotten worse. Bought the truck and they had replaced the wires/plugs to it so I decided to hell with it I just put premium in it and not much of a problem it doesnt do it unless I gun the gas.

The last 10k miles or so its been shuttering at the 2k RPM range (has 142k miles at the moment). This weekend I went through replaced both ignition coils put on new bosh wires some good plugs etc. I gapped for .055 and #4 STILL miss-fires. I made sure I replaced the clamp above the small radiator hose thats above the #4 so that shouldnt be leaking to trigger a miss-fire. When I removed the plugs there was some dirt/oil buildup on them but nothing bad at all. Anyone have any ideas?

 

I have the same year, same engine. I had the #4 misfire, but it was caused by a coolant leak from the heater hose. It sounds like you checked for the leak already. You might need to install factory plug wires, or quality aftermarket wires. I don't know if the Bosch wires will work well or not.

I had put Bosch plugs in a few months back and it ran so-so. Then when the misfire started, I bought new Motorcraft plugs from the dealer. I tightened up the heater hose, cleaned up the #4 plug wire and injector plug, and installed the new plugs. It runs smoother now and no misfire.

 

Sounds like the only thing left is the fuel injector.