1999 1500 Sport, 5.2/5 speed, 236K miles.

So, took to mechanic to replace radiator, look at other things. Detected a missfire in the #8 cylinder, also 80 psi compression in same cylinder.

The vehicle was purchased with the CAT removed by several owners previous, check engine light is on, white exhaust smoke and oil consumption, #8 plug was badly oil fouled but has since been replaced.

After reading all the "plenum" threads, my theory is this. The dreaded factory plenum plate gasket has failed, pushing oil toward the #8 cylinder (possibly others). As a result, the CAT got plugged up, hence why owner sometime prior removed it. With the oil pushing through, I believe the #8 valves are so carboned up that it's causing the low compression and misfire.

This is my plan, let me know if I'm missing something. I have bought a 2nd "Keggar" intake for a '98 5.2. My plan is to clean it, then add either a Hughes Performance or other suitable plenum repair plate. I'm thinking that while it's there, to replace both cylinder heads, in esscence, a top end rebuild. With the new heads and repaired Keggar, After heads are on, but before intake, want to change cap, rotor, plugs and wires. Once that is complete, to the muffler shop for a universal CAT and maybe a flow master for kicks.

And I on the right path here? I really didn't want to do a whole long block if possible.

TIA

 

You have 236K so it may be time for a rebuild. Do a leak down test and that will tell you if it's the valves or the rings.