That's a compression test.  The fit a pressure gauge with a hose into a
spark plug hole and crank the engine (after the engine is warm).  This
gives the BMEP (Brake Mean Effective Pressure) of the cylinder.  All
cylinders should be within 15 to 20 percent of each other.  Readings below
120 indicate a possibility of a rebuild (for most engines).  Hope this
helps.

----------
> From: Christopher M. Smith <csmith@sdsc.edu>
> To: Multiple recipients of list <vanagon@lenti.med.umn.edu>
> Subject: Leak Down Test, define ?
> Date: Tuesday, December 10, 1996 7:06 PM
> 
> 
> What is meant by a "leak down test" ?
> 
> I'm having a problem with power (loss) in my 82' Vanagon. The tech
> suggested a do a leak down test to determine why I have "massive" power
> loss on the #3 & #4 cylinders. I had the car in the shop for an unrelated
> sensor adjustment 
> 
> I am going to do a compression check (dry & wet) ASAP, is this what is
> meant by a "leak down test" ?
> 
> Thanks, Chris