I have been wanting to learn to do this but don't have the equipement. Can someone tell me where the best price is on the tools needed, and how do you do this? Do you need to remove the intake manifold? Any other special tools or skills needed?
thanks,
Paul

I got the GM compression test adapter for about $12 from toolsource.com They also sell the guage for under $100 I think. I adapted my VW guage to work with the GM adapter.

First, thoroughly warm up the engine. My haynes manual says to install some intake crossover thing. I don't know what that is and I haven't used it. All I've done is remove all eight glow plugs, then install the adapter in a glow plug port, attach the guage, and crank the engine. Make sure you first disconnect the fuel shut off wire from the injection pump, otherwise you will be spraying fuel out the other ports and the port being tested might want to fire. If you don't know which wire it is, just unhook all the wires from the IP. If you don't have an assitant to crank the engine, you can make things easier on yourself by attatching a wire to the relay terninal on the starter (this is the terminal with only one small wire connected to it). Then run the wire to a simple on/off switch and then to the positive terminal on a battery. This way you can crank the engine while standing over the engine compartment holding the guage.

Crank the engine over 6-10 times and record the highest reading you get. Don't pour oil into the cylinder to see if the compression improves (indicating bad rings/cylinder walls) like you would in a gas engine. The oil could ignite under the compression.

Crank the engine over 6-10 times and record the highest reading you get. Don't pour oil into the cylinder to see if the compression improves (indicating bad rings/cylinder walls) like you would in a gas engine. The oil could ignite under the compression.

So, how do we rule out the bad rings/cylinder if oil use is forbidden? Is there any other way to determine problem than pulling the head, checking the valves, and if those are ok, then it's the rings/cylinder?

Another good reason for not putting some oil in the cylinder is that you could break the piston rings. It would be difficult to get the oil into the cylinder since the diesel has a pre-combustion chamber where the actual ignition of the fuel/air mixture occurs.

It would be difficult to get the oil into the cylinder since the diesel has a pre-combustion chamber where the actual ignition of the fuel/air mixture occurs.

That's a good point. Didn't even think about that.

I was talking about this with my brother, who works with Volvo-trucks, and he told that they lock the engine from the flywheel and use pressurised air to determine faulty cylinders. Makes sense to me, just screw air chuck in place of glowplug, and then feed 30 bars (400 PSI) of air in to the cylinder. Engine needs to be locked so it won't turn when air is fed to cylinder. Then ears sharp, and if air comes from crankcase, it's the rings, and if from exhaust/intake manifold, valves are the problem.