Your harbor frieght compression tester is meant to be used through the injectors holes on the 617 engines. Not sure there is an adapter in the kit that will allow you to go through the GP hole. I have the same kit.

There is some arguement wether it's better to test compression on a cold or hot engine. To me the compression on a cold engine is far more important than that of a hot engine. A hot diesel is much easier to start, even with pretty poor compression. A cold engine with poor compression is much harder to start or won't start. A hot reading will give you a more acurate reading of what the compression is when the car is warm and running, but the cold compression will tell you what you are dealing with when you go to start the car in the morning.

As for doing the test. You screw the adapter in. Plug in the gauge, and crank the engine and watch the gauge go up until it stops going up. And thats your compression. If you do go through the GP holes you'll need to remove the injector lines or wire the stop lever down, to keep the engine from starting. Also if you take all the GPs out you'll reduce the draw on the battery and starter, because it won't be fighting the compression of the other cylinders to turn over.

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