How to Check Valve Pressure
- 1). Remove one end of the the coil wire from the distributor; just pull it loose with your fingers. It's the wire in the center of the distributor, typically the shortest one. The distributor is the round, black plastic cap on top of the motor. All of the spark plugs plug into it in a circle. All cars have distributors and they look almost exactly the same.
- 2). Pull the spark plug wire off the first cylinder. Place the spark plug socket on the end of the spark plug. It will fit down over the spark plug and attach to the spark plug. Attach the ratchet to the socket and remove the spark plug by cranking the ratchet counter-clockwise.
- 3). Screw the compressoion gauge into the hole where the spark plug came out. Screw it in with your fingers, finger-tight only.
- 4). Get into the car and turn over the engine three times. The engine won't start because the coil wire is off.
- 5). Climb back out of the car and read the gauge. Write down the number. If the gauge is turned sideways, unscrew it and take it off; the needle will stay locked at the highest pressure reading. Screw the spark plug back in and put the spark plug wire back on.
- 6). Move to all the successive cylinders, removing the spark plug wires and the spark plugs, checking the pressure and then replacing the spark plugs one by one. A healthy engine valve pressure reading is 180 psi on the gauge. If your cylinder is within 20 psi of this reading don't worry about it. If the pressure drops significantly below 180 psi, you might have a bad valve.