Hummer H1 (2006+). Manual - part 171

3-26 Fuel, Emissions, and Exhaust

___________________________________________

    8

Repair or replace the fuel return line between fuel selector valve and the 
engine.

Did you correct the condition?

Go to step 10.

- -

    9

Repair or replace the fuel return line between fuel selector valve and the fuel 
tank.

Did you correct the condition?

Go to step 10.

- -

    10

1.

Install and connect all components or fuel lines that were previously 
removed or disconnected.

2.

Operate the vehicle in order to verify the repairs.

Did you correct the condition?

System is ok.

- -

 High Pressure Fuel System Diagnosis

 STEP

 ACTION

 YES

 NO

    1

NOTE:

If the engine fails to start perform STEP 2.

1.

Remove the fuel return rubber hose from the rear of the left fuel rail and 
plug the hose to prevent fuel leakage.

2.

Install a section of rubber fuel hose on the fuel pressure relief valve con-
nection and place it in a clean fuel container.

3.

Start and idle the engine.

4.

Command the fuel rail pressure to 160 MPa with a scan tool.

5.

Observe the fuel hose and container for fuel leakage.

Did fuel flow into the container?

Go to step 11.

Go to step 3.

    2

NOTE:

Only perform this test when the fuel is more than 65°F (18°C).

1.

Remove the air duct from the air cleaner assembly and the turbo inlet.

2.

Remove the fuel return rubber hose from the rear of the left fuel rail and 
plug the hose to prevent fuel leakage.

3.

Remove the relay that supplies ignition 1 voltage to the fuel injection con-
trol module (FICM).

4.

Crank the engine for 15 seconds while observing the fuel pressure relief 
valve hose connection for fuel leakage.

Did fuel leak from the fuel pressure relief valve at the hose connection?

Go to step 11.

Go to step 3.

 Fuel Return System Diagnosis

STEP

ACTION

YES

NO

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 Fuel, Emissions, and Exhaust  3-27

    3

NOTE:

The engine cranking speed must be more than 150 RPM during the

cranking portion of this test.

1.

1.Remove the relay that supplies the ignition 1 voltage to the FICM, if it 
was not previously removed.

2.

Remove the fuel return hose from the fuel injectors of the right cylinder 
bank.

3.

Connect the yellow hoses from J 45873 Fuel Return Volume Test Kit to 
the J 45873-30 Fuel Injector Test Adapters.

4.

Connect the J 45873-30 with yellow hoses to each fuel injector return port 
of the right cylinder bank, and install the retaining clips.

5.

Install the 4 yellow hoses in the J 45873 graduated cylinders in numerical 
order.

6.

Connect the fuel return hoses to the J 45873-30 to prevent leakage.

7.

Crank the engine in 15-second intervals, with 1 minute cooling time 
between intervals, until fuel starts to flow into all of the graduated cylin-
ders.

8.

Elevate the 4 hoses to retain the fuel in the hoses, and empty the 4 gradu-
ated cylinders into a suitable container.

9.

Install the 4 yellow hoses in the J 45873 graduated cylinders in numerical 
order.

10. Crank the engine for 15 seconds.
11. Measure the quantity of fuel in each of the graduated cylinders. Refer to 

Fuel System Specifications for the desired quantities (Figure 3-15).

Were any of the fuel quantities more than the specified values?

Go to step 4.

Go to step 5.

    4

1.

Remove the fuel feed pipes from any fuel injectors that have high return 
flow and install the EN 47589 Fuel Pressure Adapter Cap to the fuel rail 
outlets.

2.

Elevate the 4 hoses to retain the fuel in the hoses, and empty the 4 gradu-
ated cylinders into a suitable container.

3.

Install the 4 yellow hoses in the graduated cylinders in numerical order.

4.

Crank the engine for 15 seconds.

5.

Using the Retesting Fuel Injector Return Flow Values table, measure the 
quantity of fuel in each of the graduated cylinders. Refer to Fuel System 
Specifications for the desired quantities (Figure 3-16).

6.

Remove the fuel feed pipes from any uncapped fuel injectors that have 
high return flow and install the EN 47589 to the fuel rail outlets.

Did you complete the action?

Go to step 5.

- -

 High Pressure Fuel System Diagnosis

 STEP

 ACTION

 YES

 NO

3-28 Fuel, Emissions, and Exhaust

___________________________________________

    5

NOTE:

The engine cranking speed must be more than 150 RPM during the

cranking portion of this test

1.

Remove the fuel return hoses from the fuel injectors of the left cylinder 
bank.

2.

Connect the yellow hoses from the to the J 45873-30.

3.

Connect the J 45873-30 with yellow hoses to each fuel injector return port 
of the left cylinder bank, and install the retaining clips.

4.

Connect the fuel return hoses to the J 45873-30 to prevent leakage.

5.

Crank the engine in 15-second intervals, with 1 minute cooling time 
between intervals, until fuel starts to flow into all of the graduated cylin-
ders.

6.

Elevate the 4 hoses to retain the fuel in the hoses, and empty the 4 gradu-
ated cylinders into a suitable container.

7.

Install the 4 yellow hoses in the graduated cylinders in numerical order.

8.

Crank the engine for 15 seconds.

9.

Measure the quantity of fuel in each of the graduated cylinders. Refer to 
Fuel System Specifications for the desired quantities (Figure 3-15).

Were any of the fuel quantities more than the specified values?

Go to step 7.

Go to step 6.

    6

Were any fuel injector lines capped off during either cylinder bank testing?

Go to step 10.

Go to step 11.

    7

1.

Remove the fuel feed pipes from any fuel injectors that have high return 
flow and install the EN 47589 to the fuel rail outlets. 

2.

Elevate the 4 hoses to retain the fuel in the hoses, and empty the 4 gradu-
ated cylinders into a suitable container.

3.

Install the 4 yellow hoses in the graduated cylinders in numerical order.

4.

Crank the engine for 15 seconds.

5.

Using the Retesting Fuel Injector Return Flow Valves table, measure the 
quantity of fuel in each of the graduated cylinders. Refer to Fuel System 
Specifications for the desired quantities (Figure 3-16).

Were the fuel quantities more than the specified value at the uncapped fuel 
injectors?

Go to step 8.

Go to step 9.

    8

Repeat the fuel injector return flow test with capping until no fuel injectors 
have high return fuel flow.

Did you complete the action?

Go to step 9.

- -

    9

1.

Replace the fuel injectors that had capped off lines (Refer to section 3).

2.

Install all disconnected and removed fuel system components.

3.

Start and idle the engine. You may have to prime the fuel system before 
the engine will start.

4.

Command the fuel pressure control to 160 MPa with a scan tool.

Is the fuel pressure more than 145 MPa?

Go to step 12.

- -

 High Pressure Fuel System Diagnosis

 STEP

 ACTION

 YES

 NO

___________________________________________

 Fuel, Emissions, and Exhaust  3-29

Fuel System Speci cations

The fuel return from the fuel injectors to the tank will vary based on the API value of the fuel. Measure the Fuel API with the
Diesel Fuel Quality Tester. For this reason the Fuel System Diagnosis - High Pressure Side values will vary for identifying a fuel
injector or fuel pump concern. Use the following tables when referred to by the diagnostic. The first table is to be used during the
initial diagnosis to identify the worst fuel injectors. After the fuel injectors that fail the first part of the test are capped off, the return
flow from each uncapped fuel injector must be measured again. This is because the fuel system is returning less fuel to the tank,
and thus the fuel pressure is higher during the retest. Failure to use the correct table may result in the replacement of good fuel
injectors.

Figure 3-15:   Initial Fuel Injector Return Flow Values

Figure 3-16:   Retesting Fuel Injector Return Flow Values

    10

Replace the fuel injection pump (Refer to section 3).

Did you complete the replacement?

Go to step 12.

- -

    11

Replace the fuel pressure relief valve (Refer to section 3).

Did you complete the replacement?

Go to step 12.

- -

    12

NOTE:

The fuel system may have to be primed before starting the engine.

1.

Install and connected all fuel system components that were previously 
removed or disconnected.

2.

Operate the vehicle in order to verify the repairs.

System is ok.

- -

 Initial Fuel Injector Return Flow Values

 API Rating

 Maximum Single Fuel Injector Return Flow

30-34

3 ml

35-39

4 ml

40-44

5 ml

 Retesting Fuel Injector Return Flow Values

API Rating

 Maximum Single Fuel Injector Return Flow

30-34

4 ml

35-39

5 ml

40-44

5 ml

 High Pressure Fuel System Diagnosis

 STEP

 ACTION

 YES

 NO