Pull the fuel pump relay, pull all 6 plugs, block the throttle open, crank the engine until the pulses no longer move the gauge upward. A warm engine will give you better readings if you can. If you get low readings, a few drops of oil in the cylinder may boost readings if the rings are worn. A leakdown test (with compressed air) can tell you if your valves are leaking, if you have no compression at all in all 6 pots, then check for a broken timing belt and associated bent valves. If you have zero compression in only a few cylinders, then you may be dealing with 'lawnmower' syndrome where the lifters have collapsed due to very short running cycles.

DEWFPO
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1998 S90 077,400 and 1995 964 154,100