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 provide an overview of each diagnostic category.

### Circuit/System Description

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the primary fuel tank 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.

An electric turbine style fuel pump attaches to the primary fuel tank module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter, past the fuel pressure regulator, and through the fuel feed pipe to the fuel injection system. The fuel pressure regulator has a T-joint that diverts the needed fuel to the fuel rail with the unused fuel dropping back into the reservoir of the primary fuel tank module. The primary fuel tank 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.

The primary fuel tank module also contains a primary jet pump and a secondary jet pump. Fuel pump flow loss, caused by vapor expulsion in the pump inlet chamber, is diverted to the primary jet pump and the secondary jet pump through a restrictive orifice located on the pump cover. The primary jet pump fills the reservoir of the primary fuel tank module. The secondary jet pump creates a venturi action which causes the fuel to be drawn from the secondary side of the fuel tank, through the fuel transfer pipe, to the primary side of the fuel tank.

### Diagnostic Aids

• | A vehicle that runs out of fuel above empty may indicate a condition with the siphon jet pump, or transfer lines between the fuel tanks. Inspect for blockage, foreign objects or restrictions in all related hardware.

• | A vehicle that runs out of fuel above empty may be caused by an inaccurate fuel level sender. Inspect the float arm for binding, or obstructions.

#### 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 42964-1 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.

• | DO NOT start the engine.

1. Ignition ON, command the fuel pump relay ON with a scan tool. You should hear the fuel pump turn ON and OFF for 3-5 seconds.

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

2. Ignition OFF, all accessories OFF, install the J 42964-1 and J 34730-1A .
3. Ignition ON, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 380-410 kPa (55-60 psi) and remains steady for 5 minutes.
4. Operate the vehicle within the conditions of the customers concern while monitoring fuel related parameters with a scan tool.

⇒ | If the scan tool parameters do not indicate a lean condition, refer to Symptoms - Engine Controls .

### Circuit/System Testing

1. Ignition ON, command the fuel pump relay ON with a scan tool and observe the fuel pressure while the fuel pump is operating. Verify the fuel pressure is between 380-410 kPa (55-60 psi).

⇒ | If the fuel pressure is more 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 for the following:

• | Restricted fuel feed pipe

• | Restricted or plugged fuel filter

• | Restricted or plugged strainer

• | Stuck or binding fuel level float

• | Restricted siphon jet pump

• | Restricted transfer lines between fuel tanks

• | Faulty fuel pressure regulator

• | Poor connections at the harness connectors and ground circuits of the fuel pump

⇒ | If you find a condition, repair as necessary.

⇒ | If all components test normal, replace the fuel pump.

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 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. | Open the valve on the J 42964-1 .

2.3. | Bleed the air from the fuel pressure gage.

2.4. | Close the valve on the J 42964-1 .

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

⇒ | If the fuel pressure remains constant, replace the fuel pump.

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

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. Remove the J 42964-1 and J 34730-1A .
5. Operate the vehicle within the conditions of the customer concern while monitoring fuel related parameters with a scan tool.

⇒ | If the scan tool parameters indicate a lean condition, test/inspect for the following:

• | Restricted fuel feed pipe

• | Restricted fuel filter

• | Restricted siphon jet pump

• | Restricted transfer lines between fuel tanks

• | Faulty fuel pressure regulator

• | Poor connections at the harness connectors and ground circuits of the fuel pump

⇒ | If all components test normal and the scan tool parameters indicate a lean condition, replace the fuel pump.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Primary Fuel Tank Module Replacement

• | Fuel Injection Fuel Rail Assembly Replacement