cranking psi

[1bad383]

I am looking for the GM specs on the cranking psi on the 6.5's. I've looked and looked, but cannot find them. I have a range of 300-360. Just trying to troubleshoot for my recent power loss. Thanks for your help!

[More Power]

A cylinder pressure of 275 psi is considered (by GM) to be the lowest acceptable limit for the 6.2/6.5. The lowest cylinder should not be 10% or more below the highest reading cylinder. Typical cranking pressures range 350-400 psi.

How the cylinder compression test is performed can make a difference. Perform this on a warm engine, and take the reading after no less than 4 "puffs" (compression strokes). Battery and starter condition can play a part in pressures. Need at least 200 rpm cranking speed. A worn engine cranked at 300 rpm could read pressures equal to a fresh engine at 200, so it takes some interpretation - as does whether all the glow plugs are removed or only one cyl at a time.

For the most meaningful information, cranking rpm, engine temperature, and whether all or one glow plug(s) are in/out should be included in the final analysis. :)

Jim

[1bad383]

Thanks for the info. I did remove all the glow plugs, except for #6. PITA to remove downpipe to get to it..... The motor does spin over pretty good, and the motor was fairly warm when it was checked. So it is starting to look like the power loss problem is in the top half of the motor. IP, injectors, timing chain & heads.