Engine basic condition - how to check
by: Cobalt327
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[edit] Checking engine's basic health
First thing is to look at is all the fluids and the air filter to get an indication of how the engine was maintained. Check the oil for water and the water for oil. Either can indicate a blown head gasket or cracked block.
Remove the breather and PCV to look for obvious signs of sludge. Check cooling system for rust and the radiator for clogged tubes or evidence of leaks that could have caused overheating.
Next, start the engine and warm it up. Remove one spark plug wire at a time using an insulated spark plug boot puller, noting any change in idle speed. If the idle speed drops, that cylinder was firing. Go through all the plugs and if there was a plug or plugs that the idle speed remained unchanged or nearly so, the next step is to see if it's a problem with the plug or wire. Remove the plug wire from the weak cylinder and swap it with a plug and wire from a cylinder that was working normally. If the weak cylinder is now OK, it was either the plug wire or the plug. Swap the wire from the weak cylinder with another good wire and see the results. If the miss followed the wire, the wire is bad, If not it's the plug.
If the miss did not follow the plug or wire, that cylinder or cylinders need to have a compression test performed on them. With the throttle propped wide open and the ignition disabled, crank the engine over letting the cylinder come up on compression three times. Note the reading. Next, squirt oil into the cylinder through the plug opening and test again. If the reading doesn't change, likely the valves aren't sealing. If the pressure comes up, there's a good chance it has worn or possibly broken rings.
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