Fuel Article - ASD Controlled Lift Pump

  If the ECM is no longer powering the electric lift pump and you’re using a manual switch wired directly to the fuel pump relay for control there is a danger of the fuel pump feeding a fire in the event of an accident even if the engine stalls.  The automatic shutdown relay is an alternative that will turn the fuel lift pump off if the engine stops and still be able to prime the VP44 if needed.

  The automatic shutdown relay (ASD) in the power distribution center (PDC) is energized by the powertrain control module (PCM) by grounding pin 85 of the relay when the engine is started.  This closes the contacts and battery voltage is supplied to terminal 87 of the relay.  The terminal 87 of the ASD relay supplies power to the PCM through a 14 gauge dark green/orange (DG/OR) wire.  When the engine stalls the PCM opens the grounding circuit within 3 seconds and the voltage is removed from terminal 87.

  The lift pump relay can be controlled by connecting a wire between terminal 87 of the ASD relay, or splicing into the DG/OR wire) and terminal 86 of the lift pump relay.  The power draw of the lift pump relay solenoid is less than 1 amp so an 18 gauge wire can be used.

There is an option to run the lift pump without the engine on, a bypass switch and second relay can be installed.  The second relay is used to isolate the PCM and not power up systems unless the key is in the on position.  Also if the bypass switch was wired directly to pin #86 of the fuel pump relay the amp draw from the PCM would blow the 3 amp fuse.

   If installed improperly the lift pump could stay on in the event of an accident.  Installer/user assumes responsibility for proper installation and use.   

Written by: J. Daniel Martin, Martin’s Mobile Maintenance

AKA: IBMOBILE

3/24/19

View full Cummins article