pounds of compression per cylinder
3 - 4 per cylinder.
I have a 2005 and compression should be close to 120 psi. Normally a good engine will have compression between 115 and 130 psi but a leak down test should be performed also to know the full condition of a cylinder.
The ratio is 9.5.1 in the 350 vortec. Doing a compression test you should not have any below 100 psi and all should be similar to each other.
compression test or leak-down test.
Just did compression test on mine and the normal seems to be 160 -180
Cylinder bleed down.
Oil burning or loss of compression on any one cylinder. It may also be missing on one cylinder. A compression test will verify this.
You will have to do a compression test yourself to know that. A engine that is in good shape should have at least 150 LBS. per cylinder. There can not be more then 20 LBS. difference in any cylinders. It has to have at least 100 LBS. for the cylinder to fire at an Idle.
Do a compression test on each cylinder looking for one that is significantly lower than the others.
This all depends on why it has low compression. If the rings are worn out, the motor should be rebuilt. If one of the valves is bad, re grinding it or replacing them is the fix. Perform a cylinder leakage test to confirm it. You will probably need to take it to a shop for this, but unfortunately, there usually are no quick fixes for low compression.
The easiest answer is when it fails a compression test. Buy a compression tester (farily cheap), and test each cylinder. If one single cylinder is below 120 psi, or if one cylinder reads 15% less pressure than the cylinder with the highest pressure, your engine should be torn down and checked. The problem might only be in the heads, but it's still time for some serious work.