Compression Test on a 6.2

[SoMnDMAX]

Doing a compression test on a friend's 6.2. What should I expect to see for readings? 300 PSI seems to be the norm, except on one cylinder, which tests at 100 PSI (obviously not good).

Is 300 PSI good/bad/indifferent? Haven't figured out what the cause of the low compression is in the bad cylinder, but I'm thinking it's an exhaust valve judging the way it runs (ran). It popped and smoked badly on that bank.

Tried searching for my answer, but unfortunately the crash ate it... :(

[britannic]

Batteries should be fully charged and cranking speed needs to be over 200rpm; it's more important that the compression values are consistent. More than a 15% difference between cylinders needs investigating.

With a cranking speed above 500rpm and 6 puffs from each cylinder, anything over 275psi is considered to be healthy.

Cylinders that don't build up pressure are indicative of leaking valves, worn out rings etc., a 20% difference can be caused by worn cam lobes.

[SoMnDMAX]

Thanks for the reply!!

Suprisingly, the compression on the seven good cylinders was relatively close- no more than a 20 PSI variance.

Worn cam lobes... Never though of that...