Question about Cars & Trucks
How low is it? Usually any cylinder that is less than 75% of highest cylinder compression is a problem. They should all be close to each other for good balance and power. Any cylinder below about 100 psi will be misfiring.
If one is very low, yes, the head will have to be removed to find the problem. Could be a valve not sealing or a head gasket failure. If you want to be certain of what the problem is, you could have a leak-down test of the cylinder done before removing the head. About 100 psi compressed air is held in the cylinder, and wherever the air is escaping points to the problem. A bad intake valve will have the air coming out the intake manifold. A bad exhaust valve will have air coming out the exhaust. A failed head gasket will have air escaping where the gasket lets compression escape, like the radiator sometimes, or sometimes into the crankcase, or sometimes outside the engine where the block and head mate. It's another diagnostic test, if you want to spend the money to have it done.
If the engine overheated, be sure and check the head surface for warping or cracks.
Posted on Jul 18, 2013
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Posted on Jan 02, 2017
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