Diesel Tech Tips - How to Perform a Relative Compression Test

The relative compression test is a simple, easy test that can save you, your techs, and your customers hours of frustration and headache. It just requires a current clamp and oscilloscope to test all cylinders at the same time.

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[freestonediesel]

Thanks for the video! Just used this method. I jumped wires to a core 6.7 injector I had and used a 2nd channel to watch voltage spike. I thought the issue was #1, but it ended up being the companion cylinder #6 exhaust rocker arm bridge fell off, causing no compression release. Thanks again?

[markmacias]

How can you tell if its a good relative compression test, or you have a starter drawing to much amperage. How would you tell the difference between the two possibilities.

[עודדרף]

Hi Michael nice video.
I bought the scope that connects to the diesel laptop.
Is there a way to study your course remotely?
I am reaching out to you all the way from Israel, is there any way you can assist me in taking the course from here?
I also work with the Jaltest on tractors and am interested in this too.

[torquesnhorses]

If the engine failed a relative compression test, does it always mean a problem to compression? I'm thinking a parasitic load from faulty accessories like the AC compressor, alternator, air compressor, drive pulley and belt can greatly affect the cranking effort of the motor. Will this test lead you to a wrong diagnosis?

[stevesauerland]

Nice video. Assuming you used a 2000 amp clamp? Also, if you have multiple battery cables how do place your amp clamp? Thanks

[jamesstanley]

Good video, you cant differentiate cylinder compression in that way tho, your only checking the when the pintle opens and closes do to the signal its receiving. It does not give you an in cylinder compression or integrity. I like how you are using and oscilloscope tho.