OK, here is what I got. 1990 460 EFI engine with Great vacuum, very steady. The engine has just over 37,000 miles and burns 1 quart of oil in 1 hours time. Whether it is on the expressway and averaging 50 miles / hour or if it is in the city and only doing 30. 1 hour operating time and I have to add 1 quart of oil.

Cylinders #1 through #7 have 193 psi to 200 psi. #8 had 75 psi. Spark Plugs with 37,000 (approx miles) on #1 through #7 looked great while #8 was oil fouled to the max.

I loaded the #8 cylinder with air and there was none coming out the intake or the exhaust. I pulled the PCV valve and heard the air coming out through the grommet, along with some fumes. So I have either rings or a cracked piston.

I installed 8 new plugs and all plug wires. I ran some Ris-Lone Ring Sealer and Marvel Mystery Oil in the crank case for about an hour and then let it cool down. I checked the compression again on #8 and the compression went up to 110 psi. The #8 spark plug was again oil fouled. I changed the spark plug in #8 hole and added 1 quart of oil once again and drove the motorhome about 30 miles. I re-checked the compression on #8 cylinder for a third time and it went up to 135 psi. However the coach now smokes like a BEAR after it is warmed up.

Ok, it seems to be rings on #8. I am wondering if the rings will finally free up, given enough time and still using more detergents.

Also, could this possibly effect the injector? I am wondering if the injector is coked up so that the cylinder is not firing at full strength to help free up the rings.

Help ... if someone knows of a better way to free up the rings with out tearing down the engine, feel free to step in. The location of this engine will mean that I have to drop it out the bottom of the motorhome even to pull the heads. UGGGGGH!

I am thinking that the valve guide seals might also be in bad shape. I can get the valve covers off, with a little work. Any suggestions?

"Doc"

 

Sounds like you either melted hole in the top of the piston or more likely burnt the outside edge of the piston, taking out the rings. The only real way to know is pull the head, but I will bet the engine needs a rebuild. There is no way a valve seal can let a quart thru in an hour of running.