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what is the proper way to run a cylinder compression check?

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I think I might have a head gasket issue. I got the gauge to check the compression but I've never done this before.


I won't have anyone to help me do it, can I actuate the starter solenoid by running a wire to it from the + battery?


If I do that, do I need to disable the fuel pump? If so, where is the relay or fuse located?


Do I need to ground the center wire going to the distributor when I remove it if I'm just actuating the starter? I'm going to remove all the plugs at one time and test cylinder to cylinder.


Any tips appreciated, like I said this is my first time doing it I don't want to mess up my ignition system or start a fire. Thanks.

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Remove all spark plugs

disable the ignition(I like to disconnect right at the coil)

Dry test:

With tester in place , crank the engine for 3 secs , check guage , note the pressure , release pressure from guage , remove and go to next cylinder ( I always do a double , sometimes triple check)(crank time really depends on the starter , if really slow , go 5 secs )


Cylinder pressures do range . Safely , they should fall between 120-150ish and all be with 10 psi of each other .


If you have a low cylinder(by low I mean below 120 , or signifigantly out of range from other cyls) , you'll need to do a wet test . This can tell you what the problem is for low compression .

On the low cylinders , squirt a litttle oil , maybe tblspoon or less , into the cylinder , do the compression test again . If compression increases (say 10psi+) it would indicate either ring or cylinder issues . If compression stays the say , it would indicate a bad valve seating or simply a bad valve .


Hope this helps


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  • 5 months later...
How are you guys holding the throttle plate open?


I was going to run a compression test today but I didn't let the engine warm up. And I didn't want to dump all the heat I just got working in the garage. :ack:

Pretty much anything will do. I use a pc of broom stick stuck in the throttle body. A screwdriver handle works good too. Anything that'll hold the plate at least half way open.
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If you use a remote starter switch, you can activate the starter without turning on the ignition, and you won't need a helper to turn the key. If you don't already have a remote starter switch or two ... you should.

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