Leave all the spark plugs in except for the cylinder you’re testing. You’ll need a breaker bar or long- handle ratchet and socket to turn the crank nut.
1. Warm up the engine, so the rings have a chance to seal.
2. Pull the spark plug out of the cylinder you want to test.
STEP 1: Remove the fuel pump and fuel-injection fuses. Disconnect the main wire to the coil and spark plug wires; remove spark plugs.
STEP 2: Start the threaded end of the compression gauge in a spark plug hole by hand.