What valve is it? I-2 or I-3 by chance? If it is, the low pressure for bypass has not been set correctly. Remove valves, inspect car up, adjust screw til you get 0 motion, turn screw in until it creeps, then back it out slowly til zero again. Stop pump, take screw out 1/2 turn again, and voila, low pressure has been set for the I-2 or I-3.
This can contaminate the up leveling speeds so you may need to re adjust that as well.
