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Old 03-14-2019, 06:53 PM   #2
OldNuc
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Join Date: Apr 2008
Location: Far Southwestern Iowa
Posts: 66,694
 

1998 SC2
Default Re: Proper way to do compression test?

To prevent washing the cylinders down with fuel remove the PCM B fuse to shut off the fuel pump, injectors, and ignition before starting the test. Remove all spark plugs and block the throttle open. Use a low charge rate battery charger to fully charge the battery before conducting the test.

Crank the engine until the gauge quits increasing and compare both the final pressure and number of compression strokes to reach the max pressure, cylinder to cylinder. You can do this test either cold or hot or warm just mention it when stating results.

For example if you find all cylinders produce a final reading of 200psi but the compression cycles are as follows: 1-8, 2-6, 3-8, 4-14 then it should be obvious that cylinder #4 has a serious problem with leakage past either the valves or compression rings.

FSM states the MINIMUM number of compression cycles is 10 and a Fully charged battery is required to obtain the full 250RPM cranking speed.

Nominal compression for a high mileage good condition DOHC is 190-220psi and SOHC is 175-205psi.


Do not screw it into the head past the point the sealing o-ring just contacts the head. Do not overtighten as it will leak.
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