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

The engine control module (ECM) supplies voltage to the fuel pump control module (FPCM) when the ECM detects that the ignition is ON. The voltage from the ECM to the FPCM remains active for 2 seconds unless the engine is in Crank or Run. While this voltage is being received, the FPCM closes the ground switch of the fuel pump and also supplies a varying voltage to the fuel tank pump module in order to maintain the desired fuel rail pressure.

The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel pump module, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel pump module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of the flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel pump module. The function of the venturi pump is to fill the fuel pump module reservoir. The fuel pressure regulator, a part of the fuel pump module, maintains the correct fuel pressure to the fuel injection system. The fuel pump module contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

#### Special Tools

• | CH 48027 Fuel Pressure Gage

• | J 37287 Fuel Line Shut-Off Adapters

### Circuit/System Verification

Note:

• | 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 OFF, all accessories OFF, install the CH 48027 Gage . Refer to Fuel Pressure Gage Installation and Removal.
2. Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 345-414 kPa (50-60 psi) and remains steady for 5 minutes.

### Circuit/System Testing

Note:

• | 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 345-414 kPa (50-60 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

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

Note: 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 more than 34 kPa (5 psi) in 1 minute.

⇒ | If the fuel pressure decreases more 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 Shut-Off Adapters between the fuel feed pipe and the fuel rail.

2.3. | Open the valve on the J 37287 Shut-Off Adapters .

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 Shut-Off Adapters .

2.6. | Verify that the fuel pressure does not decrease more 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 more than 14 kPa (2 psi) in 5 minutes.

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

4. Operate the vehicle within the Conditions of the customer's concern while monitoring the fuel pressure with the CH 48027 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 sender.

• | Restricted fuel feed pipe

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

5. If the fuel system tests normal, refer to Symptoms - Engine Controls.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Fuel Hose/Pipes Replacement - Chassis

• | Fuel Injector Replacement

• | Fuel Tank Fuel Pump Module Replacement