During a compression test, a cylinder has 40 percent of the specified compression reading. When the technician performs a wet test, the compression reading on this cylinder has 75 percent of the specified reading. The cause of the low compression reading could be:

Worn out piston rings

Explanation:

Here there is increase in the pressure during the wet compression test. Since, the pressure reading from 40 percent of the specified compression reading raised up to 75% of the specified reading.

The cause of the low compression reading could be Worn out piston rings that is allowing the pressured to be released and hence the compression reading is low.