What symptom or problem are you trying to solve?
When doing a compression test, the engine should be warm, and you should have a battery charger connected, on a slow charge rate. As the cylinders are tested, the battery runs down, so the last cylinder checked will be lower due to slower cranking speed, and cold piston rings that do not seal well.
The compression test only tells you when a cylinder is low. It does not tell you why. For that you need to perform a cylinder leakage test. That involves forcing in compressed air, through the tester, into the spark plug hole after the piston is brought to top-dead-center on the compression stroke. The gauge on the tester will show the percent of leakage. Next, you observe at four places to determine the cause. If you hear hissing at the tail pipe, the exhaust valve is leaking. Hissing at the throttle body means the intake valve is leaking. Hissing at the "oil" cap or dip stick tube indicates leaking piston rings, and a steady stream of tiny bubbles in the radiator points to a leaking cylinder head gasket.
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Monday, January 29th, 2018 AT 2:21 PM
