Older Cat D4 (40A3910) with electric start diesel engine seems to have lost pump pressure and will not start. We have changed the fuel filters and bleed the system to no end. It has always started and ran just fine in the past. Maybe another possibility might be the mechanical shut off at the throttle is stuck somehow? Anyone having a suggestion as to what might be the problem it would be greatly appreciated. Thanks

take the plate off of the injector pump, turn engine over, see if the 4 plungers go up and down. some times the plungers will stick in the up position, so no fuel is pumped.

This engine would be a D330 so would have the later compact fuel housing on it and there is no side plate to remove and the pumps set down inside the housing. I,m kind of confused as to what 612 your saying as I take it you can hand pump fuel but the transfer pump isn,t pumping. Take the little cover off the front of the inj. housing and have someone work the throttle and see if the rack bar is moving inside that little hole under the plate as the rack might be sticking.Also turning engine over are you getting any fuel while trying to bleed the pumps with the throttle on or out the filter bleed screw? Make sure with the main fuel line from the tank off see if your getting a flow from the tank.

The 40A uses the compact fuel injection pump system....there is no side cover to remove. Are you getting good fuel flow from the tank to the transfer pump?
Check the pressure relief valve at the transfer pump for crud preventing the relief valve from seating.

Thank you all for the replies. In one way or another they all seem to help. Anyway the D-4 now starts and runs as good as ever. The problem turned out to be with the mechanical shut off by way of the throttle position. The rack within the pump stuck in the shut off position. There is a oil line from the motor to lubricate the pump. By pulling the oil line off and spraying carburetor cleaner into the rack area through the oil line seemed to break the rack loose and into the starting position. Thanks again for the help.