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

[abugarcias]

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.

[NewfieMJ]

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

Newf

[1987Comanche]

Hot engine with throttle fully open, correct?

[terrawombat]

I normally keep the throttle plate fully open.

[NewfieMJ]

Sorry , meant to mention that as well . Throttle wide open and I prefer the engine warmed up .

[Thunderbear]

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:

[JACKED88]

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.

[87Chief]

If possible, it's much easier with two people. Person sitting in the seat pushing pedal to floor and another watching the gauge.

[Geonovast]

Best way to disable the ignition is to unplug the coil and the CPS. unplugging the CPS will also disable the injectors, so you won't be spraying gas into the cylinders while doing this.

[Eagle]

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.