Circuit/System Testing

NOTE:

The fuel pump may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
DO NOT start the engine.

Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating. Verify the fuel pressure is between 345- 690 kPa (50-100 psi).
- If the fuel pressure is greater than the specified range, replace the fuel tank module.
- If the fuel pressure is less than the specified range, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank module.
  - Restricted fuel feed pipe
  - Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
Verify that the fuel pressure, after the fuel pump is turned off, decreases to 500-599 kPa (72-87 psi), and does not decrease more than 34 kPa (5 psi) in 1 minute from that point.
- If the fuel pressure stays above 600 kPa (87 psi), replace the fuel tank module.
- If the fuel pressure decreases greater than the specified value, perform the following procedure:
  1. Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief (With CH-48027) or Fuel Pressure Relief (Without CH-48027) .
  2. Disconnect the chassis fuel feed hose from the engine compartment fuel pipe.
  3. Install the J 37287: Shut-Off Adapter between the chassis fuel hose and the engine compartment fuel pipe.
  4. Open the valve on the J 37287: Shut-Off Adapter.
  5. Ignition ON, command the fuel pump ON with a scan tool and bleed the air from the CH 48027: Gage or the CH 48027-100: Gage.
  6. Command the fuel pump relay ON and then OFF with a scan tool.
  7. Close the valve on the J 37287: Shut-Off Adapter.
  8. Monitor the fuel pressure for 1 min.
    - If the fuel pressure decreases more than 34 kPa (5 psi) within the specified time, locate and replace the leaking fuel injector(s).
    - If the fuel pressure does not decrease greater than 34 kPa (5 psi) within the specified time, replace the fuel tank module.
Relieve the fuel pressure to 69 kPa (10 psi). Verify that the fuel pressure does not decrease greater than 14 kPa (2 psi) in 5 min.
- If the fuel pressure decreases greater than the specified value, replace the fuel tank module.
Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH 48027: Gage or the CH 48027-100: Gage. The fuel pressure should not drop off during acceleration, cruise, or hard cornering.
- If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank module.
  - Restricted fuel feed pipe
  - Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
If the fuel system tests normal, refer to Symptoms - Engine Controls and Fuel Injector Solenoid Coil Test .