Testing Compression while hanging from engine crane, need help - Ford Powerstroke Diesel Forum
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post #1 of 3 Old 12-23-2009, 05:20 PM Thread Starter
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Testing Compression while hanging from engine crane, need help

I have a 7.3 hanging from a engine hoist, I hooked-up starter and batteries (4 of them for good measure and fast crank).

Using a known working digital diesel comp. tester, I was unable to get readings on this engine though I can hear/feel the engine sucking and pushing air (glow plugs out).

Being that this engine timing runs off a CPS, am I ever going to get any reading (same thing that happens when cps goes out on the road).

Number one, two and four cylinders show some small movement of valve springs, the rest just lay there like a dead dog.

I was able to get number one hole to push my gauge to 46 psi. Two injectors are currently removed, but can't see how that would affect comp in other holes.

I just wanted to see if this engines rings/valves held any psi and what kind of life it may have left before I go to the trouble of dropping it into a vehicle.

Any ideas on if this engine hang test is possible would be great.
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post #2 of 3 Old 12-24-2009, 07:27 AM
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Does the tester plug go in the engine through the gp holes? Either way if you hear "sucking and pushing" then you need to seal that up. Compression is built in a sealed area. As far as your valves...are all of them tight like they are supposed to be. I e rocker arms. I am still learning the diesel setups so I could be way wrong.

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post #3 of 3 Old 01-18-2010, 07:06 AM
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I realize I’m seeing this post rather late but, you need oil pressure to make the lifter work and make the valves work. Having an injector out might cause the oil pressure not to build up because of all the oil just dumping out the injector hole, not to mention the chance of oil dumping into a cylinder causing later hydro lock. The cam sensor will have no effect because the electrical side just fires the injectors, compression is completely mechanical. You should be seeing around 400 psi if you got good oil pressure and she is cranking good. You are doing it correctly having all 8 glow plugs out so that only the test cylinder is building pressure and the other 7 are sucking and pushing. You need oil pressure.

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