For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Circuit/System Description

When the ignition is turned ON, the engine control module (ECM) supplies power to the in-tank fuel pump, by energizing the fuel pump relay. The in-tank fuel pump remains ON as long as the engine is cranking or running and the ECM receives crankshaft reference pulses. If there are no reference pulses, the ECM turns the in-tank fuel pump OFF, 2 seconds after the ignition switch is turned ON or 2 seconds after the engine stops running. The electric fuel pump is incorporated into the modular fuel pump and sender assembly and is located inside the fuel tank. The fuel pump supplies fuel through a fuel filter, also located in the modular fuel pump and sender assembly, through the fuel feed pipes, to the fuel rail assembly. The fuel pump provides fuel at a pressure above the pressure needed by the fuel injectors. The fuel pressure regulator, located in the modular fuel pump and sender assembly, keeps the fuel available to the fuel injectors at a regulated pressure. When the fuel pressure rises above the pressure regulator calibration, the pressure is relieved, with excess fuel exhausted into the modular fuel pump and sender assembly reservoir.

### Reference Information

#### Description and Operation:

Fuel System Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

#### Special Tools Required

• | J 34730-1A Fuel Pressure Gage

• | J 37287 Fuel Line Shut-Off Adapters

### Circuit/System Verification

Important:

• | Inspect the fuel system for damage or external leaks before proceeding.

• | Verify that adequate fuel is in the fuel tank before proceeding.

• | The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

1. Ignition ON, command the fuel pump relay ON with a scan tool. You should hear the fuel pump turn ON and OFF.

⇒ | If the fuel pump does not operate, refer to Fuel Pump Electrical Circuit Diagnosis .

2. Ignition OFF, all accessories OFF, install the J 34730-1A . Refer to Fuel Pressure Gage Installation and Removal .
3. Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 380-427 kPa (55-62 psi) and remains steady for 5 minutes.

### Circuit/System Testing

Important:

• | The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

• | DO NOT start the engine.

1. Ignition ON, 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 380-427 kPa (55-62 psi).

⇒ | If the fuel pressure is greater than the specified range, replace the fuel pump.

⇒ | If the fuel pressure is less than the specified range, remove the fuel tank and test, inspect, and repair the items listed below. If all items test normal, replace the fuel pump.

• | Restricted fuel feed pipe

• | Restricted or plugged fuel filter

• | Restricted or plugged strainer

• | Stuck or binding fuel level float

• | Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.

Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.

2. Verify that the fuel pressure does not decrease greater than 34 kPa (5 psi) in 1 minute.

⇒ | If the fuel pressure decreases greater than the specified value, perform the following procedure:

2.1. | Ignition OFF, relieve the fuel pressure. Refer to Fuel Pressure Relief .

2.2. | Install the J 37287 between the fuel feed pipe and the fuel rail.

2.3. | Open the valve on the J 37287 .

2.4. | Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the fuel pressure gage.

2.5. | Close the valve on the J 37287 .

2.6. | Verify that the fuel pressure does not decrease greater than 34 kPa (5 psi) in 1 minute.

⇒ | If the fuel pressure drops, locate and replace the leaking fuel injector.

2.7. | If the fuel system test normal, replace the fuel pump.

3. 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 minutes.

⇒ | If the fuel pressure decreases greater than the specified value, replace the fuel pump.

4. Remove the J 37287 and J 34730-1A . Refer to Fuel Pressure Gage Installation and Removal .
5. Operate the vehicle within the conditions of the customers concern while monitoring fuel related parameters with a scan tool. The scan tool parameters should not indicate a lean condition.

⇒ | If the scan tool parameters indicate a lean condition, test for a restricted fuel feed pipe, restricted fuel filter, or poor connections at the harness connectors and ground circuits of the fuel pump. If all test normal, replace the fuel pump.

6. If the fuel system components test normal, refer to Symptoms - Engine Controls .

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Sender Assembly Replacement

• | Fuel Injection Fuel Rail Assembly Replacement