Well, I had a wild hair to do a compression test on my Bonneville last night and I am severely disappointed with my results.

I only tested the front 3 cylinders (I hate shoving the tester in the back 3). Cylinders 1, 3, and 5 I think.

Cylinder 1 (or 2): 95 psi
Cylinder 3 (or 4): 110 psi
Cylinder 5 (or 6): 130 psi.

If I'm not mistaken, 130 is normal. The closer I get to the tranny, the more pressure is lost. What could cause this, besides an old and work engine?

How many miles on the motor?

I assume these were tested with the throttle wide open correct? I had the same situation for the longest time before I realized my shortcoming.

I don't know the engine miles, but the chassis says 307,600. Maybe original motor, maybe not. I has NO idea.

The throttle wasn't open at all. Just unhooked the coilpack ECM and cranked with the tester plugged in. Does the throttle affect it?

I think it does, because it is trying to draw air through a mostly closed throttle plate. Experts? Throttle open or closed?

Throttle needs to be full open. Also test with a warmed up engine and get 5 to 10 good cranks on for a good test. Test all cylinders and if you have more than a 10% difference between the highest and the lowest reading, you are getting in the area to where you may need t look at a rebuilt motor.

The amount of compression you have is not important unless it'* really low, it'* a balance between them all, 10% max difference. Here'* a write up on doing a compression test.
https://www.gmforum.com/trouble-shooting-test-procedures-141/compression-test-284387/

as stated above

warm engine, throttle wide open.

balance between cyls is more important then the actual number

Thanks guys. I'll do it again with WOT here soon. It was warm last time I did it, and I'll warm it again. That makes it a pain in the *hands* cuz the exhaust is just right there with the spark plugs!

Just as another note there are two ways to do the test...first off all the responses are correct lol. u can also do a test where ya squirt a bit of oil in the empty spark plug hole and then crank it over if it holds your rings are good if it bleeds down they re getting worn if i recall correctly...