All of the fuel system tests will require operation of the fuel pump to measure pressure, evaluate pressure decay, or perform the pressure at the calibrated flow tests.

Although the fuel pump can be controlled with the ignition, this is fairly awkward since:

The scan tool provides control of the fuel pump at the technicians finger-tips. The tool will run the pump for 30 seconds after the ON command. This timer will then shut the pump OFF.

Important: Once the fuel pump is commanded ON with the scan tool it will be energized for 30 seconds before it times out and returns to the OFF status. Do not leave the vehicle unattended while running any of the system tests with the pump ON.

The scan tool also controls the pulsing of the injectors and pressurizing the system during the Injector Balance Test 8.

Operating the Fuel Pump/Injector Balance Test

Control of the fuel pump and injector are under the Special Functions menu.

The fuel system tests outlined in the fuel system diagnostic flow chart and detailed procedures (Tests 1-8) provide a systematic approach to determining whether the fuel system, from the fuel pump to the fuel injectors, is functioning as intended.

For the engine to operate as designed, the fuel supply system must deliver fuel at the proper pressure with adequate volume and maintain pressure after the engine and fuel pump are turned OFF.

In addition, the fuel injectors must deliver the precise quantity of fuel at exactly the correct intervals with no leakage of fuel when the injector is turned OFF.

The battery of tests outlined in the Fuel System Diagnosis flow chart are designed to evaluate all the performance characteristics. Symptoms or complaints related to the fuel system include:

Diagnostic trouble codes associated with fuel supply problems include DTC P0171 and P0172.

Important: The performance of the fuel pump (pressure and flow) is very dependent on supply voltage. The voltage must be above 12 volts when running any of the diagnostic tests. Published test specifications cover the range of system operation from 12-14 volts, but are biased towards the lower voltages (12-12.7 volts) since all tests are run with the engine OFF. All accessory loads should be OFF when running any tests (DRL's, interior lights, radio, etc.) to provide maximum available voltage for the tests. If voltage is below 12 volts, the battery must be charged before running the tests.

Test 1 - Fuel Pump Operational Test

Test to establish whether the fuel pump is operating and providing fuel to the injectors.

Test 2 - Fuel Pressure at Idle (or engine Off) Test

Basic integrity test of the fuel system to determine whether the regulated operating pressure is achieved under low load conditions.

Test 3 - Fuel Pump Flow/Pressure Test

Actually a series of 4 tests (3A, 3B, 3C, and 3D) to determine if fuel pressure is within operating limits while simulating the flow demand of the engine running at wide open throttle. These tests are run with the engine OFF and provide a means, based on testing at 4 points in the system, of determining if the fuel feed line, fuel pump, and the fuel filter are operating to design specifications.

The testing is performed using the SA9127E-7 fuel flow/pressure test adapter which incorporates a precision orifice to meter 50 liters/hr at a delivery pressure of 380 kPa (55 psi) for the 2.2 liter (L61).

The flow/pressure adapter consists of:

It is connected with the inlet side to the fuel feed, the outlet side to the fuel return (or drain), and the gage port to the pressure gage or cap. The ON/OFF control valve provides a means to control the fuel flow for pressure and leakdown testing.

The test criteria is the fuel pressure read while the fuel pump is energized. Refer to Energizing the Fuel Pump, with the engine OFF. If the pressure measured is within specification then the fuel supply is capable of meeting all volume requirements of the engine.

Test 4 - Fuel Pressure Regulator and Return Lines Integrity Test

Actually a series of 3 tests (4A, 4B, and 4C) to determine if the fuel pressure regulator or fuel return lines are operating properly.

Test 5 - Fuel System Pressure Leakdown (Decay) Test

Actually a series of 3 tests (5A, 5B, and 5C) to determine if the fuel system will maintain pressure after the engine and fuel pump are shut-off. Fuel pressure must be maintained after shut-off to ensure quick restarts and prevent fuel vapor from forming at the fuel rail, causing hard or extended cranks. The tests are arranged to allow isolating the problem components or area by evaluating the components in sequence.

Test 6 - Fuel System Pressure Test

Actually a series of 2 tests (6A and 6B) used to determine the cause of low fuel pressure. The 2 tests are designed to isolate faulty components, such as the fuel pressure regulator, fuel pump, or fuel filter. This is accomplished by measuring pressure using the SA9127E-7 fuel flow/pressure adaptor in 2 locations.

Test 7 - Fuel Injector(s) Tip Leakage Test

This test determines if fuel injectors are leaking fuel into the intake system. Leaking fuel injectors can cause problems with extended cranks, hard starting, and rich running conditions (DTC P0172).

Test 8 - Fuel Injector Balance Test

This test determines if fuel injectors are metering an equal quantity of fuel when they are commanded open. By measuring fuel pressure drop during a timed cycle of opening each injector, a relative evaluation of each injectors flow rate is made. This test is designed to identify injectors with significant differences in flow rate but will not identify problems with an injector flow pattern (e.g., improperly sized spray cone, non-uniform spray cone (pattern), mis-directed spray cone, etc.)

Tools Required

SA9127E Gage Bar Set

Caution: Refer to Relieving Fuel Pressure Caution in the Preface section.

Prior to servicing any fuel system components, such as the fuel rail, injectors, filter, pressure regulator, fuel tank, fuel pump module, etc., any pressure built up in the system must be relieved. There are 2 preferred methods:

1. Start and run vehicle then disable the fuel pump with the scan tool.

This method is the cleanest since no fuel, under pressure, will be present at any fitting or connection that needs to be serviced.

This method is preferred when removing any components of the fuel system that require disconnecting fuel lines. If performance tests are to be run on the system underhood, procedure 2 will be preferable since the SA9127E will also be required for the testing.

This method is also preferable to disconnecting the fuel pump relay since no DTCs will be set and there is no concern about voltage spikes to the ECM if the relay should be installed with the key ON.

1.1.	Connect the scan tool and start the vehicle.

1.2.	Turn the scan tool ON and locate Special Functions.

1.3.	Select Powertrain.

1.4.	Select Fuel System.

1.5.	Select Fuel Pump.

1.6.	Command the fuel pump OFF.

1.7.	The engine will die in 3-5 seconds. Turn the key OFF, and proceed with component removal/installation.




2. Bleed pressure at the service test port.

This method will require collection of fuel as pressure is relieved. Use of a suitable container is required.

Caution: Refer to Gasoline/Gasoline Vapors Caution in the Preface section.

2.1.	Locate the service test port on the fuel rail and remove the protective cap.

2.2.	Connect the gage bar 53476 to the fuel gage pressure adapter 309725 using a flexible hose from the SA9127E .

2.3.	Make sure the needle valve on the pressure adapter is closed (OFF).

Notice: Do not use any tools to tighten the adapter to the fuel line pressure port. If the adapter will not seal with finger tightening, then the seal is defective or damaged and needs to be replaced. Excessive torque on the adapter will damage the fuel line test port.

2.4.	Connect the pressure adapter to fuel line test port.

2.5.	Route the drain hose from the pressure adapter into a suitable container or route the fuel back to the fuel tank.

2.6.	Open the valve on the pressure adapter and bleed off the pressure and fuel.