Do I need a rebuild or is there something else to check? Misfire on cylinders 5 & 6. Ford diagnostic reveals 5 at 125 PSI and 6 at 105 PSI.
Internal problem is conclusion. It uses no oil. Has no noise, tapping or knocking. No antifreeze in crankcase. Any option other than tear it down? This is the 2nd engine. 1st started knocking at 192k. This is a used engine. In at 65k now has 95k on it. Sad, but I may have to let it go.

 

Miss fire likely isn't caused by the difference in compression. Pull the spark plugs and see what they look like. Low compression could be caused by worn valve guides, carbon build up. What is the compression on the rest? Miss fire could be bad plug, coil pack, wire (if yer motor has one). Need more info, investigation. What vehicle and motor do you have?

 

Thanks for responding. I really like this truck and don't want to lose it. It is a 5.4L vinL. I had new plugs, COP's and injectors installed and ran seafoam through the gas supply.