Just finished a leak down test... and I'll say that even if you buy the tool, rent a compressor and buy the hose/couplings to adapt... it's STILL cheaper than taking it in! Even I can't mess it up.

Any insight or experience with these tests/the results I got is a huge help as always

found 0 bubbling in the coolant, 0 hissing/leakage from exhaust... did find through the oil filler cap hole (right name?). Plugs are normal looking @ the ground/tip, looks like fresh oil around the edge/ring though

#1 - 17-17.5%, some leakage/hissing @ oil cap
#8 - 15-15.5% some leakage/hissing @ oil cap
#4 - 18.5-20% some leakage/hissing @ oil cap
#3 - 19-21% some leakage/hissing @ oil cap
#6 - 13 firm... loud leakage/hissing @ oil cap
#5 - 15 firm... loud leakage/hissing @ oil cap
#7 - 11-11.5% semi-loud leakage/hissing @ oil cap
#2 - 15% moved slowly from 100% to 15% semi-loud leakage/hissing @ oil cap

No bubbles in coolant/rad.. no hissing leakage from exhaust

 

I probably missed this in another thread, but I assume you are doing this test because you have an issue. When I have done leak down tests in the past I have pulled the valve cover and first did one when visually seeing that both the intake and exhaust valves are closed. If they still leak then I loosen the rocker arm to make sure I don't simply have one too tight. If you do one cylinder at a time and back each one off the same exact amount then when you are done with that cylinder you can tighten it back exactly where it was. With the valve cover in place it is too easy to have a valve slightly open. Did you try listening through the throttle body. Usually if you have an exhaust valve issue you will hear it at the exhaust and if you have an intake valve issue you will hear through the throttle body/carb.

 

I'm going to do the test again today like you specified with the valve covers off... it seems a little more in depth than sticking a screw driver in the plug hole.

Playing dumb here, how does a rocker arm that is too tight affect the leakage?
I would do this to both intake and exhaust rocker arms at the same time, or one at a time? Or play around with it a bit?

So when I heard it through the oil filler on the valve cover, it could have been that the valves weren't completely closed?

I will listen through the tb, I didn't think of that!

 

I guess I should have asked what year - if they are adjustable then tightening too much can cause a valve to remain open. The newer trucks just torque down although I have had a later model 4.3 that was running rough actually have a cracked rocker arm cradle that when torqued was going down too far (due to the crack) and therefore the intake valve was never fully closed. This resulted in a cylinder with zero compression. Have you tried a compression check. That is usually the first thing I do when doubting compression and then if I find a cylinder with none I do a leak down test to see if it is intake or exhaust.

Yes if a valve is not completely closed then it will leak into whichever valve is open - intake or exhaust.

 

1992 1500 305, should be adjustable