Low Compression on 525? (new problem, new thread)
 

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.

Probably broke when your wife used it for a hammer . :whistle:

i had a similar problem with my old snap on tester,the schrader valve was bad,i replaced the schrader and all is well.

I could try that. There is one inside and another on the outside to release the pressure. I'll put a new one on the inside and try it before I buy a new one. That won't take long.

Yay! 135 psi, engine cold, throttle closed. Manual says 140 w/engine warm & throttle open. I'm good! So this morning I'm looking at my 30+ year old compression tester and I'm like, ah, no, not gonna try to fix it. Bought a new one. :)

good deal...cheaper than engine repair !

Good news. You can now resume breathing. LOL

im glad your problem turned out to not be a real problem,no go and buy a lottery ticket because you are lucky.

Thanks guys. I was worried there for a little while. I lost a Bravo XR upper this year from a nut backing loose inside and the money tree has been plucked clean. Now to finish the winterizing and get ready for another Michigan winter. :(

and carl,,when its time for a valve job look into a set of afr heads....

Does a 6 ft. hose give a lower reading?

Not to hijack but.....these are related questions.

I always here people say that a leak-down test is a better determination of what's going on inside an engine. I know how a compression test is done, have a gauge, and can do that myself.

What is involved with a leak-down test? What is the procedure? How much for tools?

How much could I expect to pay to have a leak-down done?

Since I don't wrench professionally anymore I just bought a leakdown tester at Harbor Freight for $40. Procedure can vary but what I do is pull all plugs, use a remote starter switch to bump the engine over while I hold a finger over the spark plug hole until I hear and feel the compression stroke. Then I put a long thin screwdriver in the cyld and rock the engine back and forth by hand until I can feel that the piston is at TDC. Otherwise the air will push the piston down. Now inject the air into the cyld following directions as some testers work differently. If leakage is excessive then listen at throttle body/carb, oil fill, exhaust to hear where the air is escaping. I've done lots of these tests on cars. I'd loosen the belt on a marine engine first (water pump). You can also use a fully degreed harmonic balancer but my way works good. I used to use the test as a back up if the compression test showed a problem. Leakdown will tell you if it's an intake valve, exhaust valve, rings or head gasket or crack.

Thanks for the info. It does sound a little more complicated than a compression test.

a compression will tell you if something is wrong
a leak down test will tell you whats wrong