Simple question: I did some leakdown testing today. My input pressure is 100psi. When I start the test sometimes it goes right to 97-98 psi, but other times it goes to around 80 psi. It seems that it will stay there until the piston moves to BDC.

This seems to happen on many cylinders. Is this normal, or does it indicate some problem with the motor?

-ch

 

The piston isn't supposed to move during a leakdown test. You have to get that particular piston to tdc before adding pressure. I am guessing that it takes around 80 psi to move the piston and thats why it stays there until bdc.