What does a differential pressure compression tester indicate if a cylinder will not hold pressure after rotating the crankshaft?

A differential pressure compression tester is a diagnostic tool used to evaluate the sealing capability of a cylinder within an engine. When a cylinder does not hold pressure after rotating the crankshaft, it signifies that there is a failure in achieving the necessary compression within that cylinder.

In this context, a cylinder failing to hold pressure typically indicates that there is a loss of compression either due to improper sealing between the components (like the piston rings or valves) or potentially through an internal leak. A normal indication would be that a cylinder maintains pressure, reflecting that it is sealing appropriately.

In cases where no pressure is held after the crankshaft is rotated, it suggests that there is indeed a concern that warrants further investigation, such as worn piston rings or malfunctioning valves. While one of the choices refers to a potential problem with the piston rings, the correct interpretation is to conclude that if there is a failure to hold pressure, it signifies an abnormal condition that deviates from expected engine performance, rather than a normal operational state. Therefore, the failure to hold pressure is consistent with recognizing an abnormal indication.