i'm in the garage now so hoping someone knows this off the top of their head:

should a leakdown test be performed with all plugs out, or only the the cylinder being tested? we're getting very different readings depending on which way we do the test.

thanks,

tony

I take the plugs out but only to make it easier to turn the motor by hand. I can't see how the cylinder under test would be affected by the other cylinders unless there is a leak from one cylinder to the next (bad head gasket, crack, etc.)

Let us know the results so we can help you more. I did mine with plugs on, and that did not affect on the results

If the cylinder under test is not at TDC, the compressed air can in theory turn the crank and in turn (pun) decrease the pressure through increased volume.

The other chambers should not affect the results (a measurement of sealing) however, if the plugs are in the other cylinders, they would be more reluctant too turn when driven by the piston under test.

Here is how I would do it:

All plugs out

Test cylinder at TDC

Engine in 5th with Ebrake on