Quote:
Originally Posted by jake12tech
the peak psi on a new engine is 418psi according to the service manual IIRC.
Giants, I don't think you're doing the compression test correctly. you have to hold the pedal WOT for two compression hits or 5 seconds and quit. that's why you're seeing such high cylinder pressures.
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The maximum rated PSI I've seen quoted is 30bar, which is around 450PSI. That's assuming a NEW engine with perfect valve seating and no cylinder wear. I'd expect a 300K engine to be somewhere in the mid 300's.
WOT means nothing on these diesels, there's no throttle plate. The injectors or glow plugs should be removed, so there's no compression on the untested cylinders either.
As a rule of thumb, the first compression hit should get you somewhere around 50% of your max reading, and you should have the max reading after 3-4 hits. You can crank all you want after that and it should make no difference at all. A low first hit, or a slow buildup to max reading is a sign of low compression, even if the final compression number is acceptable.