Compression test numbers

Capri306 · 03-02-2001, 08:18 PM

With a warm (not hot) engine, pull all of your plugs, disable the fuel pump (inertia switch) and the ignition system (DO NOT just pull the coil wire, disconnect the plug going into the coil!). Then you screw the end of the gauge's hose into a cylinder, hold the throttle open about ¼ of the way, crank for about 4-5 seconds, then see what the gauge says. Repeat for all cylinders. Oh, here's my numbers I got today:

172-172-174-172-172-176-172-172

Not too shabby for an all-stock engine with 110,000 miles, eh?

Chipdog: it seems you have a vacuum leak, and it sounds like it's in your PCV system. Let's keep the possibility of bad injectors on the back burner for now. Replace the PCV valve & screen under it, check that and ALL other vacuum hoses for leaks, and pray for the best. BTW, what oil pressure do you have at idle and cruising? What grade of oil are you using?

As to your low compression numbers, do as directed above and try pouring 1-2tbsp of oil into the cylinders to see if compression is raised. Good luck.

------------------
Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch

[This message has been edited by Capri306 (edited 03-02-2001).]

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03-02-2001, 08:18 PM	#4
Capri306 Moderator Join Date: Sep 1998 Location: Grand Rapids, Michigan, USA Posts: 1,001	With a warm (not hot) engine, pull all of your plugs, disable the fuel pump (inertia switch) and the ignition system (DO NOT just pull the coil wire, disconnect the plug going into the coil!). Then you screw the end of the gauge's hose into a cylinder, hold the throttle open about ¼ of the way, crank for about 4-5 seconds, then see what the gauge says. Repeat for all cylinders. Oh, here's my numbers I got today: 172-172-174-172-172-176-172-172 Not too shabby for an all-stock engine with 110,000 miles, eh? Chipdog: it seems you have a vacuum leak, and it sounds like it's in your PCV system. Let's keep the possibility of bad injectors on the back burner for now. Replace the PCV valve & screen under it, check that and ALL other vacuum hoses for leaks, and pray for the best. BTW, what oil pressure do you have at idle and cruising? What grade of oil are you using? As to your low compression numbers, do as directed above and try pouring 1-2tbsp of oil into the cylinders to see if compression is raised. Good luck. ------------------ Capri306, Moderator, The Mustang Works Online 1979 Mercury Capri, 5.0L -- C4 -- 2.73 1987 Mustang LX Notch [This message has been edited by Capri306 (edited 03-02-2001).]