Your piston rings are probably bad, but 1st make sure you don't have too much oil in the motor and that the oil isn't thinned by having fuel mixed in.

The proper test for worn piston rings is called a leakdown test which requires compressed air pumped into 1 cylinder at a time. There's a special tool that has a gauge that usually reads a percentage of leakdown and the cylinder being tested needs to be at top dead center which is when the piston is at it's highest point and both valves are closed.

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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com