I apologize for the long post, but I feel that the more detail, the better.

'05 1500 4.7L QCSB 4x4 w/5-45RFE with 142k

About 6 months ago the check engine light came on and the associated code was P0303. I was at about 130k, and it had been about 60k since I did the spark plugs, so I went ahead and swapped them out. Number 3 looked a little worse for the wear, but not terrible. The truck was happy.

Fast forward to 3 months ago. CEL comes on again. P0300 & P0303. Check all the plugs again. Number 3 has a cracked insulator, but the rest look good. I replace the bad plug, and, for the heck of it, swap the coils between 1 and 3. P0301, now we're getting somewhere. I swapped out all 8 coils, and the truck was happy again.

This week, you guessed it: P0303. Cracked insulator again. There is also a new almost imperceptible vibration on the driver's side while accelerating. I ran a compression test, and all 8 cylinders came out with similar readings. I'm not leaking any fluids, there is no coolant in the oil or vice versa, so I'm reasonably sure a head gasket is not to blame. But I'm stumped as to what else could be the issue. Any help would be greatly appreciated.

Cheers

 

Swap injectors on 1 and 3. See what happens. If the injector is partially clogged, it could be running that cylinder lean... (which would explain the cracked insulator.)

 

Inspect the harness for #3 coil. If it's chaffed, then an electrical short could be causing the repeating problems with #3.

 

That is odd, I am working on a neighbor's Charger R/T 5.7 with a bad #3 misfire and when I popped the #3 plugs out they both were smashed closed. I replaced the plugs and a coil but still a misfire persists, They aren't closed anymore.
I then swapped #3 coil with #5 and it still has a miss but the cel does not come on anymore.
I did notice that I only had 85 lbs. compression on that cylinder in both plug holes but ran outta time to test any other ones.
I'm going to do that tomorrow along with checking voltages on the injector and coil wires.