Compression checking

[basement]

So did a compression check and found most of the cyls are extremely low, so much that some will barely register on the gauge. Question, what kind of adaptor can i get or make so that I can pump some air into the cylinder while at TDC of the compression stroke so i can see where the air is getting past?

[mojavered]

Are you sure that the tester is holding up against the head correctly?  I had a few testers that I rented from Autozone and had to take back because I never could get them to work right.  They leaked like crazy.
Also, make sure that you have your throttle held wide open (with a rag take on the fuel while turning over) so that you are not dumping all that raw fuel down the cylinders. 

[72bluNblu]

Even if there were holes in all the pistons, it should register on the gauge. I mean, 40 psi is ridiculously low, and that should read fine on the gauge. I honestly can't recall getting a compression reading less than 50 psi on a 318, and that was on a cylinder that had a valve hanging wide open (bent valve) AND a blown head gasket.  And to get that in all your cylinders leads me to believe its not the engine.

My guess is you either have a really awful/broken gauge, or you're not sealing the spark plug hole with the adapter. I am assuming that this isn't the screw in type of compression tester.

Just for fun, could you detail the process you're using when you test a cylinder (ie, warm the engine up, remove all the spark plugs, fix the throttle wide open for the entire test, etc.) But, even if your process is wrong I can't see it not reading on the gauge. Even if you didn't do any of the things I mentioned I can't see it not reading on the gauge. The test wouldn't be accurate, but not reading on the gauge is something else.

[ireland383]

Yes, you need a good seal and a Fully charged battery.

[basement]

1) though the engine was not completely up to temp it was warm
2) pulled all but 2 of the plugs
3) used the screw in type
4) throttle wide open

And just for kicks I put the gauge on the wifes Jeep and the gauge showed compression on it, but hers was only showing 60psi which does lead me to believe there is something wrong with the gauge. Maybe I should try a different one?

[72bluNblu]

Although I would recommend pulling all the plugs, that's definitely not your problem. Sounds like your gauge is toast. Not sure what year or how many miles your wife's Jeep has on it, but I think a safe guess that gauge is probably off by 80-90 psi.

[Aussie Challenger]

*** Warning *** when doing a leak down test don't have your hands anywhere near the fan as the motor may turn over if the piston is not completely at TDC.   

[BIGSHCLUNK]

Also check the schrader valve, if t leakes even slightly..... you get the idea. We've had it happen! 

[moper]

If the car has running isues, might be the car. Do the other 6 and get back to us. The test should be with no plugs in it... And if there is no real reason other than you are curious, it's probably a bad gage...