Home » Duramax LLY » Duramax LLY – COMPRESSION TEST


1. Disconnect fuel solenoid wire at injection pump.

2. Disconnect and remove all glow plugs.

3. Thread adapter J Ð26999-30 into glow plug hole of first cylinder to be tested. Then attach compression gauge JÐ26999 to adapter.

4. Have helper crank engine through six cycles (to generate six compression strokes). Note and record gauge pressure.
Repeat procedure at remaining cylinders.

5. Minimum acceptable cylinder pressure is 380 psi (2626 kPa). In addition, lowest cylinder should be at least 80% of highest; this is maximum allowable cylinder variance.

CAUTION: Never inject oil into the diesel engine cylinders for any reason. This could result in piston and rod damage because of the minimal clearances in a high compression diesel combustion chamber.


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