Hello all,
My boys '07 MCS w/ 62k miles started acting up last week. Smoking out the tailpipe, missing at low rpm. Checked the compression and got the following readings:
Cyl 1: 180
Cyl 2: 30
Cyl 3: 160
Cyl 4: 180
Borescope showed no piston damage (visible from the top) no cylinder wall damage.
Tried pouring some oil in the cylinder and checked again, came up to 60. Thinking its the rings. Any further advice? Debating on my next step.

Thanks
Sean

 

I have seen cases where the intake or exhaust valve would break and melt away.

1- Place cyl # 2 at compression stroke (rotate the engine by hand at this point forward to not further damage the engine).
2- with the compression tools, you can remove the check valve and connect an air compressor to "pump" air into the cyl.
3- hear where the "hissing" sound is coming from "if any" to determine whether it is on the intake or exhaust side.

 

Minitobe has good advice. You need a leak down test, bet it's a bad valve..

 

Thanks guys. I'll do that this evening.

 

Well, I followed MiniToBe's advice. Sure enough air coming out of the dipstick. Next question, with Cylinder #3 being 20 #s low, should I go ahead and replace the rings on both #2 and #3 cylinders? Thanks for all the help.

 

Since you are getting the head removed anyway, might as well doing all of them. My fear is that it is might be more than rings. But you wont till you open it up.

 

Where you located by the way?

 

Fairmont, WV. About 90 Miles South of Pittsburgh. I stuck a borescope down the cylinder and didn't see any cylinder wall damage. Right now my plan is to pull the pan and just replace what I need to from there. I talked to a guy who had a similar problem but he had a hole in his piston. He was able to replace it that way.

 

Rings can only be done from top.