I would appreciate if anyone would reply with the correct procedure on how to perform a compression check on my car. I have received conflicting instructions and want to make sure I get an accurate proper reading.

I know I need to remove the coil wire, but my first question is should I remove ALL the spark plugs first, or only remove 1 plug, then test that cylinder, then replace it and move to the next plug?

Also, I have heard different stories about whether or not the fuel pump relay should be disconnected so no gas is being forced into the cylinder(s). Also, I have read articles about performing the test and some state to perform the test under WOT. Should I open the throttle while cranking the engine over a few times (or have someone push the gas pedal down)?

 

BUMP I also plan on doing a compression check very soon and would like to know the correct way.

 

You should just unplug the ignition module on the side of the distributor. This should disable fuel and spark. You don't want the pcm to pulse the injectors even if you disable the fuel pump because they will still spray fuel and mess with your readings. Remove all of your spark plugs. Crank engine under WOT for 5 seconds or five hits on the gauge. I prefer five hits. You want each cylinder to build at the same rate (reaches equal value in the same hits). You don't want more than a 10% difference between cylinders. A 5.0 is typically in the 140-160psi range. Perform this test again with a teaspoon amount of oil in the cylinder to evaluate the rings ability to seal. Too much oil may seal valves as well. Your compression should come up regardless of ring condition with a wet test but if it goes from 90 to 180psi - you know you have a bottom end issue.

 

Thanks for the post. This is the info I got, and is very close to what you say. Just wanted to make sure.

Remove all plugs, disconnect coil, disconnect fuel pump relay.

insert gauge into 1 cylinder, and with WOT (or gas pedal down) crank motor 4-6
times and record number. Repeat for all other cylinders