Checking compression
Safety Car
Joined: Jun 2004
Posts: 3,563
Likes: 2
From: Dallas Tx
The service manual says to remove all spark plugs, disable fuel sytem and ignition system. Hold throttle pedal wide open, and crank engine.
After at least 4 puffs on the gauge, that's the reading for that cylinder.
The manual says it should be between 100 and 150 and within 70% of each other. Generally on a healthy engine I will see 10% or less variation and probably around 120sh. psi.
The big thing to look for is the variation. If you've got 7 at 110 to
120sh and 1 at 70, that's leading to an issue in that one cylinder.
After at least 4 puffs on the gauge, that's the reading for that cylinder.
The manual says it should be between 100 and 150 and within 70% of each other. Generally on a healthy engine I will see 10% or less variation and probably around 120sh. psi.
The big thing to look for is the variation. If you've got 7 at 110 to
120sh and 1 at 70, that's leading to an issue in that one cylinder.
Racer
Joined: Nov 2006
Posts: 354
Likes: 0
From: New Lenox IL
Disconnect the plugs from the fuel injectors - disconnect the wiring harness that clips into the coil packs - pull spark plugs and wires. Install compression gauge - turn over 3-4 times and right down your results. As michrider said, you're looking for a variation. Anything under 120 or so is rather low...
Moderator emeritus
Joined: Jun 2001
Posts: 18,599
Likes: 3,955
From: Jacksonville Florida BWO Dayton, Cincinnati, Bloomsbury NJ, Cincinnati
2015 C7 of the Year Finalist
