first off, checking compression while the engine is running is a proven method of diagnostics.... many things in a motor change under load.

heres a good example... youve got a weak headbolt on a boosted car. compression testing the motor at idle may show decent compression numbers, while when its got load on it, it may be stretching the bolt and allowing the HG to leak.

you guys are all so gung ho to hate but experience can come from listening not just doing... and at my age... 24.... i'm gonna go ahead and listen.