I have a problem with my 1997 f150 4x4 4.6. When it is cool it runs fine until it gets warm then it misses. It is missing so bad you can hear a knocking noise in the bottom of the engine. I would appreciate any replies on this.

 

That's a little strange for a 97 F150, it it would have been almost any other car with a ignition module I would have told you to check that first, maybe it's one of the two coil packs.
When and what mileage was the last tune-up performed? DO you have any kind of check engine lights on? You could have a scan of the PCM to see if there is pending DTC's in there. Also , I just got to thinking when the engine is cold is running off of values programmed into the PCM, when it warms up it will switch to reading the sensors (like the post cat O2's).
I've had the OE wires last for 98K miles and then an aftermarket set that only lasted for 23K. I have had plugs that only lasted for 12K but the death was partailly due to a dealer who power washed the engine.

 

I changed the coil packs there was no difference. When the codes were scanned the 5 and 6 plugs are missing. This seemed to have started after i got a tank of gas. I thought maybe it was the O2 sensor but why would it just be the cylinders 5 and 6?

Baffled