Vortec Max Compression Test

[dirtdriver11]

2008 Vortec Max with roughly 250,000 miles. I keep getting random misfire codes and lean condition(P0300, P1174, P0174). I have did a smoke test on the intake and the exhaust and cannot find any leaks. Truck runs good on highway but as rough idle and goes into closed loop while at idle. I did a compression test today and here are the results. #1-160, #2-180, #3-195, #4-145, #5-205, #6-142, #7-190, #8-200. I’m not sure what the numbers should be but there are a couple weak cylinders. Anybod know what could be going on?

[Mike GMC]

You'll need to do a leak down test to see if it's valves or rings.  Was the compression test done dry or did you put a little oil in the cylinders?  My guess with that many miles, it's a bit of both valves and rings.  Some of you numbers seem quite high for a stock engine with roughly 10:1 compression.  You may also have some significant carbon build up.  Run a tank full of fuel through it with a can of BG44K and re do the test. See if the high numbers come down some. Might even smooth you idle out.

[dirtdriver11]

I did the test dry on a warm engine. I should add that I have replaced all 4 oxygen sensors, injectors, plugs and wires, fel-pro intake gaskets, and MAF sensor. 

[Black02Silverado]

It is my understanding that the compression should be within 10% of each other.  If you put some oil down in the cylinder it can help tell if it is the rings or valves.  If it goes up it is the rings, if not then the valve isn't sealing.