Compression pressure drops

If the compression pressure drops in one of the following nodes, then, according to experience, the reasons are as follows:

• intake manifold or intake damper - leaky intake valve
• open radiator or coolant expansion tank - defective cylinder head gasket or cracked cylinder head
• open oil filler or dipstick - worn cylinder walls, piston sliding surfaces or piston rings
• muffler exhaust pipe - leaky exhaust valve

Repeat the measurement process alternately on all four cylinders. More important than absolute pressure are the same pressures in the cylinders.