dry and wet compression tests
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Joined: Aug 2003
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dry and wet compression tests
I suspect I have a blow by problem with my '91 EFI 460. My question is will a compression test confirm this and if so will someone tell me the proper way to perform the test (wet and dry). Thanks in advance.
Postmaster
Joined: Aug 2001
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From: Nevada
Pull all the sparkplugs/wires, make sure your EFI is opened to the full throttle position (does this require key-on with EFI or can one hold the MAF butterfly open, I'm a carb guy?), screw the compression gauge into a sparkplug hole and crank the engine for a couple of seconds. Read compression from gauge, write it down on a pieve of paper next to the cylinder number. That's the dry test. Remove compression gauge from sparkplug hole, squirt a tablespoon or two of engine oil into the cylinder, replace compression gauge, crank engine and read compression gauge. That's the wet test.
Postmaster
Joined: Mar 2001
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From: So Cal
The other half of the answer is...
if the compression goes up a lot after the squirt of oil, then you have a problem with the rings. If it doesn't then probably the valve guides or maybe a broken ring.
The dry compression should hopefully all be within say 10% of each other, for example, you don't want to see 150, 155, 160, 100, 100, 145, 150, 145. The 100 reading indicates a problem. The double 100 indicates a head gasket problem between 2 cylinders.
Good Luck,
Jim Henderson
if the compression goes up a lot after the squirt of oil, then you have a problem with the rings. If it doesn't then probably the valve guides or maybe a broken ring.
The dry compression should hopefully all be within say 10% of each other, for example, you don't want to see 150, 155, 160, 100, 100, 145, 150, 145. The 100 reading indicates a problem. The double 100 indicates a head gasket problem between 2 cylinders.
Good Luck,
Jim Henderson
