I want to compression test my 3.8l. I have a few questions. One should the throttle be held wide open while trying to crank and test compression? Two will trying to crank six times (once for each cylinder) and holding it for five seconds everytime hurt the starter? Should I do wet tests in addition to the dry? And lastly what compression would be ideal for my 1998 3.8l? I have about 115k miles on it and have always treated it like a baby.

 

Disconnect the icm so it doesn't start while doing the test. Check one cylinder at a time and make sure the cylinder you are testing makes at least 4 compression strokes before stopping. Will not hurt starter and don't out any oil in cylinder before test as oil could hide a compression leak issue.

Honestly can't remember the psi of compression it should make but all cylinders should be very close to each other.

A better test to do is a cylinder leak down test as this tells you if rings are leaking along with valve issues where a compression test only tells you the rings are holding seal to make psi even though valves could be leaking a bit.

 

Turbo monte could I just pull of all the plug wires and take out all the plugs instead of unplugging the ICM? And how do I know when it's made 4 compression strokes?

 

I suggest unplugging icm but pulling plug wires would work I guess. Disconnecting icm will send no spark anywhere which is safer in my eyes.

Count 4 revolutions of the engine "woom woom woom woom" per say lol

 

As mentioned, disable the ICM. Remove all spark plugs and wedge the throttle open wide. Allow the engine to make 4-6 complete rotations then record the compression reading. Your lowest reading should be within 60% of the highest reading.

The only reason to do a wet test is if you have a suspect cylinder with low compression. A wet test is done by pouring a little oil into the cylinder then taking another reading. If the reading only rises by a couple of pounds the problem is with the valves or head gasket leakage. If you see a significant increase the rings are worn.

 

Right here.

I have always wondered why the fuel pump isn't disabled during this process.

 

Thanks guys. I have also heard others say to also unplug the mpi (multi-port injection) fuse to prevent the injectors from spraying during wide open throttle?

 

Some vehicles do require that the fuel pump be disabled. On these cars the pump activates to prime the fuel rails then shuts off. It won't energize again until the engine starts. Vehicles that power the pump all the time once the key is on should always have the fuel pump disabled (pull fuse).

 

What's the point of doing the "Compression" test?
R you having a problem that's prompting you to want to do a "Compression" test?

 

Stumpmi nothing wrong I'm just curious as to how close the compression is now to when it was new. It's a 98 so I just want to see what she's givin up over the years.