1999 Volvo Penta "WT" Models Workshop Manual, Page 13Get this manual
bRemove any foreign matter from around spark plugs by blowing out with compressed aircRemove and inspect all spark plugsInstall thread-type compression gauge in spark plug hole IA
dTo Prevent Sparking: All Models Except 5.0 GL and 5.7 GS: Remove (grey) 2-wire connector, with purple and grey wires, at ignition coil 5.0 GL and 5.7 GS Models Only: Remove both distributor primary wires from the ignition coil Tape wire terminals to prevent accidental grounding8
With choke andor throttle plates wide open, crank engine through at least four compression strokes
Test Conclusion The indicated compression pressures are considered normal if the lowest reading cylinder is within 75 of the highestExample: If the highest pressure reading was 140 PSI, 75 of 140 is 105Therefore, any cylinder reading less than 105 PSI indicates an improperly seated valve, worn valve guides, piston, cylinder, or worn or broken piston ringsAny cylinder reading 105 PSI or greater is within specifications, and compression is considered normalIf one or more cylinders read (ow, squirt approximately one tablespoon of engine oil on top of the pistons in the low reading cylindersRepeat compression pressure check on the cylinders1If compression improves considerably, the piston rings are at fault2If compression does not improve, valves are sticking or seating poorly, or valve guides are worn