Circuit/System Testing

Fuel Pressure Low

1. Verify none of the conditions listed below exist:
   • Restricted or dislocated fuel feed front pipe check valve
   • Restricted fuel feed pipe
   • Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
   • If a condition exists 

     Repair as necessary.

   • Go to next step: If no conditions exist 

     Replace the G12 Fuel Pump.

Fuel Pressure Leaks Down

1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief .
2. Install the EN-37287  between the chassis fuel feed hose and the engine compartment fuel feed pipe.
3. Open the valve on the EN-37287  .
4. Ignition ON, command the Fuel Pump Enable On and then Off with a scan tool.
5. Close the valve on the EN-37287  .
6. Verify that the scan tool Fuel Pressure Sensor parameter does not decrease more than 34 kPa (5 PSI) in 1 min.
   • If greater than 34 kPa (5 PSI) 

     Replace the G12 Fuel Pump.

   • Go to next step: If less than 34 kPa (5 PSI) 
7. Test for a faulty fuel feed front pipe check valve.
   • If a condition exists 

     Replace the fuel feed front pipe.

   • Go to next step: If no condition exists 
8. Test for a leaking G18 High Pressure Fuel Pump.
   • If a condition exists 

     Replace the G18 High Pressure Fuel Pump.

   • Go to next step: If no condition exists 

     Locate and replace the leaking Q17 Fuel Injector.

Fuel Pressure Drops Off

1. Verify none of the conditions listed below exist:
   • Restricted or dislocated fuel feed front pipe check valve
   • Restricted fuel feed pipe
   • Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
   • If a condition exists 

     Repair as necessary.

   • Go to next step: If no conditions exist 

     Replace the G12 Fuel Pump.