Compression Test with intake manifold removed
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Compression Test with intake manifold removed
I know I should have done a compression test first.
But in my attempt to locate the cause of coolant loss I have removed the intake manifold.
I don't really want to remove the heads unless I know the gaskets are leaking.
My idea is to modify a simple compression tester so that I can thread a fitting into a spark plug hole, put a tee on that fitting, connect a pressure guage with air release button to one port on the tee and a compressor fitting on the other port. Then I can pressurize the cylinder, disconnect the compressor, and see how fast it loses pressure. I'd have to plug the fuel injector hole and manually rotate the engine so both valves are closed.
Is this possible? Has anybody ever tried anything like this before?
But in my attempt to locate the cause of coolant loss I have removed the intake manifold.
I don't really want to remove the heads unless I know the gaskets are leaking.
My idea is to modify a simple compression tester so that I can thread a fitting into a spark plug hole, put a tee on that fitting, connect a pressure guage with air release button to one port on the tee and a compressor fitting on the other port. Then I can pressurize the cylinder, disconnect the compressor, and see how fast it loses pressure. I'd have to plug the fuel injector hole and manually rotate the engine so both valves are closed.
Is this possible? Has anybody ever tried anything like this before?
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
What your trying to do is half of a cylinder seal test that would tell you a rough percentage of leak down.
Doing such a test requires you to have a means of locking the crank from rotating because the pressure will attempt to push the piston downward same as combustion would unless you place each piston at exact top dead center for that cylinder under test.
A standard cranking compression pressure test should be good enough to pick out a cylinder down on pressure as compaired to the average of the other 5..
As far as injectors goes, removing the connectors will stop them or removing the cam position sensor connector will stop them.
Other way are removing the PCM fuse, crank sensor connector will stop all actions.
Good luck.
Doing such a test requires you to have a means of locking the crank from rotating because the pressure will attempt to push the piston downward same as combustion would unless you place each piston at exact top dead center for that cylinder under test.
A standard cranking compression pressure test should be good enough to pick out a cylinder down on pressure as compaired to the average of the other 5..
As far as injectors goes, removing the connectors will stop them or removing the cam position sensor connector will stop them.
Other way are removing the PCM fuse, crank sensor connector will stop all actions.
Good luck.
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So, it might work?
I have already removed the fuel rail with injectors. I guess I could just reinstall the rail with injectors to plug the holes. (this is a 2001, 4.2L on a F-150, XL, 2wd)
I didn't want to crank the engine because with the intake manifold removed - I thought the remaining coolant would be thrown all over the place.
Looking back at my first statement - it would work better to put the guage on one port of the tee and put the one way valve (that comes with the compression tester) between the compressor and the other port of the tee.
I have already removed the fuel rail with injectors. I guess I could just reinstall the rail with injectors to plug the holes. (this is a 2001, 4.2L on a F-150, XL, 2wd)
I didn't want to crank the engine because with the intake manifold removed - I thought the remaining coolant would be thrown all over the place.
Looking back at my first statement - it would work better to put the guage on one port of the tee and put the one way valve (that comes with the compression tester) between the compressor and the other port of the tee.
Hotshot
Joined: Jul 2005
Posts: 11,931
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the coolant leak is internal ? You could also plate over the intake maniifold ports (and water ports), then put pressure on one fitting into the water jacket, then see which cylinder the air leaks out of by putting a thumb over the spark plug hole. If the head is cracked or gasket blown on one cylinder, you would have air leak into that cylinder.
Fleet Mechanic
Joined: Sep 2003
Posts: 1,716
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I'd have to plug the fuel injector hole
I guess I could just reinstall the rail with injectors to plug the holes.
Another idea is to pull the block drain plugs and empty out all of the antifreeze, so you can crank it with the starter and do a (cold) compression test. But disable the fuel pump circuit first before cranking
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Freshman User
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You found me out. Amatures like myself should probably not be digging this deep into a motor. I think at this point I can get it back to at least the same shape it was before I started. I don't think I would pull the heads myself even if I discovered the head gaskets were bad. Thanks for the input - it has been helpful.
Postmaster
Joined: Jul 2003
Posts: 2,544
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From: okc
Do not pull the heads. Most Mod motors cannot be reassure properly without a full teardown. I know people who have done it successfully, but I know more people that tried and failed. These motors must be assembled in order so all the covers and pans line up right and seal correctly. Very difficult to do in the truck unless you have built one correctly before.
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