Running Compression Worksheet  

1.      Warm engine up only a little.  (too hot and the plugs may be hard to get out) Remove one spark plug. Ground out the spark plug wire with a jumper wire. Make sure there is no other spark plug for that cylinder, like Mustang and Ranger 2.3 L or 2.5 L engines, some Nissan engines, and some Mercedes engines. If there is another spark plug for the same cylinder, remove the plug wire and ground it out too.  Record which cylinder: ____

2.    Look at spark plug to choose the right compression hose adapter. (Similar length and width—don’t use hose adapter that is too long, the piston may hit the adapter.) Make sure the O-ring or seal is on the end of the hose. Install compression hose into the spark plug hole. Attach compression gauge to the end of the hose.

3.     Run engine at idle speed. Record compression pressure below. (You may have to push check valve to release pressure and watch pressure build up again to get an accurate reading. )

4.    Snap throttle wide open (WOT) for an instant and record the higher reading below.

5.     Repeat above steps for each cylinder of the engine.  Record your readings below:

6.    Is there more than a 20 psi difference between the idle or WOT readings? Yes ____ No ____. What do you think the readings mean? __________________ (Usually higher readings are air can’t get out with exhaust cam lobe worn down, or lower readings mean air can’t get in with intake cam lobe worn down.) When in doubt about readings, you could redo test at a set RPM, like 1500, and record the readings on the back.