Compression Test Guild Please

[TigerXiao]

Hi all

I just got the compression tester (Pittsburgh Automotive - item#69885 ) from Harbor Freight. I know that before I start the test, I need to pull some fuses.

If I am not mistaken, I need to disconnect these follow fuses and harness:
Fuel injector fuse
Fuel pump fuse
Ignition module harness
Full charge battery preferable (how do you your battery is full or not)

The problem is that when I opened the relay and fuse box under the hood, I could not locate these two fuses. Where are they located in 1996 Saturn SL? Are these steps all I need to start compression test?

[OldNuc]

You only need to remove a single fuse to shut off fuel, injectors, and spark. PCM B fuse.

Only screw that gauge into the plug hole until the o-ring just contacts the head as any more and it leaks.

Follow this.
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. Any other method has no value for comparison in a forum setting. 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.

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.

FSM states the MINIMUM number of compression cycles is 10 and a Fully charged battery is required to obtain the full 250RPM cranking speed. The FSM also does not mention counting the compression cycles and recording them. This is because the high tech recording tester counts them for you and even a blind mechanic can see the differences on the chart. As most of us are doing this with a simple pressure gauge you have to count them yourself.

[TigerXiao]

Thanks OldNuc

[underthehood]

Don't forget to block the throttle open.

[OldNuc]

That is in the instructions I posted, although it does get missed.