real quick question... how to do a compression test

[84TD]

Not for my truck but my buddy is over here and we are trying to diag his truck that is running really rough and has a lot of blowby, we bought a $29 harbor freight comp test special but looking at it I am wondering if you are supposed to do it through the injectors. And also searching around the forum I see there is a wet and dry test? What does that mean?

 

[02x72]

Not sure about the difference between a wet and dry test, Ive never heard of that. But the adapter goes into the glow plug hole.

 

['94IDITurbo7.3]

x2 on gp hole

 

[mobilemech]

you take a dry test reading of all the cylinders, write all the readings down for each hole. then you set up to do the test again but before you thread the adaptor in the glow plug hole you squirt 1 pump of eng oil in the cylinder to see how much higher the compression is, run through the test for each cylinder. it helps to diag ring or piston problems. when you start the engine up it will smoke a while. when you start the compression test, make sure the FSS on the IP is unplugged so the engine will not start.

 

[Iowa 73]

Dry test on these engines. Do not add oil to the cylinder when testing a diesel.
Pull all of the glow plugs, disable the glow plug controller, and pull the FSS plug off the IP.

 

[84TD]

thanks guys. about to make a followup thread. prognosis is not good.

 

[rhkcommander]

the harbor freight compression test kit glow plug fitting doesn't fit, unless they've updated it. you have to snip the end off and remove the shrader valve.

Remove all 8 glowplugs to make it easier to turn the engine over. Also makes it so you dont accidentally get a short start from compression and oil residue or something. I made a switch for the starter relay with 2" wires, 1 small ring terminal and 1 large coming off it so I can turn the engine over from under the hood.

 

[84TD]

the harbor freight compression test kit glow plug fitting doesn't fit, unless they've updated it. you have to snip the end off and remove the shrader valve.

Remove all 8 glowplugs to make it easier to turn the engine over. Also makes it so you dont accidentally get a short start from compression and oil residue or something. I made a switch for the starter relay with 2" wires, 1 small ring terminal and 1 large coming off it so I can turn the engine over from under the hood.

There was a long one and a short one, we used the short one. Took us a minute to figure out the adapter was bottoming out.