Cranking compression on my 525 warmed up is 88-90 psi on all cylds. I tried two testers and got similar readings but both testers are old. I squirted lots of oil in one cyld and got no increase in reading. The manual says cranking pressure should be 140 psi. I don't think I have a leak-down tester anymore but will look around some more later. I do have a way to put regulated compressed air into the cylds though. The oil test indicates good rings. Would it be normal for the valves to be worn and still get such consistent readings? Engine has about 250 hours and still runs strong. I was hoping to put off the valve job one more season. I would appreciate opinions from those familiar with the HP525 EFI that 90 psi is too low and that it's time to pull the heads this winter.

All cylinders the same, I'd be looking at timing chain and components ...

was the throttle wide open when you did the test?

something does not seem right to me...try your gauge on another engine..

Throttle was open. Engine was warm but not up to operating temp. My tools are old since I used to wrench on cars up until 1993. I might go buy a new compression tester tomorrow. Maybe a leak down tester too. I will try the tester on the Mustang. I'll do that now. brb

X2 prop ably will not run with 90

+1.. That seems way too low for the "engine to be running strong"...I'd buy a new compression tester and try again.

Thanks guys. A healthy Mustang GT just tested at 50 psi so my tester is junk. I will buy a new one tomorrow and post the results. This was an expensive Mac tester but old and gone bad. I expect to see close to the 140 psi specified with a new compression tester.

do you have a 6 ft hose connected to the tester?

No, it's a professional tester and the hoses are about two feet long. It's old and something has broken with it.