Hummer H1 (2006+). Manual - part 166

3-6 Fuel, Emissions, and Exhaust

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11. One or more injectors failing.

11. Test the injectors. Replace the faulty injectors as

needed.

12. Air leak at the intake manifold.

12. Locate with soap and water solution (or oil).

Tighten the bolts, replace the gaskets, or replace
the manifold if required.

13. Turbocharger inoperative or no boost.

13. Check the boost output. Replace the turbocharger

if compressor or turbine wheel vanes are broken,
chipped, or if the compressor shaft is seized/
broken.

14. Sensor failure (coolant or air temp, baro or 

boost sensors, etc.).

14. Locate with a scan tool. Test and replace as

needed.

15. ECM signal voltage too low.

15. Check the battery voltage and the generator output.

Repair or replace the parts as needed if voltage is
below 10 or above 16.

16. Injection pump fault.

16. Replace the pump.

Knock-Ping
Under Accelera-
tion.

1.

Contaminated, incorrect or low quality fuel.

1.

Drain, flush and refill the fuel system.

2.

Air leak in the fuel delivery system.

2.

Inspect the injector line fittings. Tighten any loose
fittings. Check all the fuel supply lines for leaks.

3.

Engine overheat caused by low coolant 
level.

3.

Repair any leaks and add coolant.

4.

Coolant and/or air temperature sensor fault.

4.

Check with the scan tool and replace as needed.

5.

Worn valve seals or guides allowing oil into 
combustion chambers.

5.

Repair the engine as required.

6.

Carbon buildup on pistons and in chambers 
as a result of substandard fuel, additives or 
oil entering the chamber past worn rings or 
through valve guides.

6.

Use combustion chamber conditioner to break
down the carbon. Engine disassembly will be
necessary if the conditioner is not effective.

Black, White, or 
Blue Smoke at 
Idle and/or 
Under Load

1.

Incorrect or substandard fuel.

1.

Drain and refill the tanks with the correct fuel.

2.

Glow plug fault (white smoke at cold start-
up).

2.

Test and replace the failed plugs, wires, or relay/
controller.

3.

Worn piston rings, valve guides or stem seals 
(blue smoke) allowing oil into combustion 
chamber. High oil consumption may also be 
noted by owner.

3.

Repair the guides, replace the seals or replace the
rings as needed.

4.

Over rich mixture (black smoke) caused by 
stuck injector.

4.

Test and replace any injectors that fail the fuel
injector balance test with TECH 2 (Refer to section
2)

 Fuel System Driveability Symptoms  (Continued)

PROBLEM

POTENTIAL CAUSE

CORRECTION

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 Fuel, Emissions, and Exhaust  3-7

Fuel System Contamination

Organic Contamination

Diesel fuel systems are susceptible to fungi and other micro-organism infestation when water is present. These fungi can grow into
long strings or large globules anywhere in the fuel system. Due to the amount of water, the most prevalent location for fungi is the
fuel tank.

The growths appear slimy and may be black, green, or brown. They are introduced by refueling with an unfiltered or aged fuel
source.

Fungi feed on the fuel and need only trace amounts of minerals and water. As they grow and multiply, they change fuel into water,
sludge, acids, and products of metabolism.

The most common symptom is a loss of performance due to fuel filter clogging. Infestation can also show up as corrosion of metal
parts such as injectors, fuel pumps, and steel lines.

WARNING:  To avoid personal injury do not come into physical contact with biocide agents, cleaners, or additives
used to remove fungi or micro-organisms.

If fungi have caused fuel system problems, sterilize the system with a diesel fuel system biocide or cleaning agent. Follow the
manufacturer’s instructions.

Use of biocides while operating under heavy loads such as towing a trailer is not recommended. Such use is permissible, but no
additional biocide should be used when refueling during such operations.

Contamination that is severe or does not respond to biocides may require tank removal, disassembly and steam-cleaning.

Water or Wax Contamination

1.

Remove the fuel cap from the filler tube.

2.

Drain the contaminated fuel into an approved container.

3.

Drain the fuel filter, fuel pump and the fuel lines.

4.

Refill the tank with fresh fuel.

5.

Start the engine and bleed the lines, filter and the injectors.

Checking Fuel Quality

The fuel quality may cause driveability problems such as hesitation, lack of power, stalling, the inability to start, etc.

For best results, use Diesel fuel No. 2 year-round (above and below freezing conditions) as the oil companies blend Diesel fuel No.
2 to address climatic differences. Diesel fuel No. 1 may be used in very cold temperatures when it stays below 0° F (-18° C),
however, it will produce a loss in power and fuel economy.

CAUTION: 

The use of Diesel fuel No. 1 in warm or hot climates may result in stalling, poor starting when the engine is hot and

may damage the fuel injection system.

A quick check on the fuel quality can be performed with tool J–38641–B.

NOTE:

The fuel quality hydrometer provides a general indication of fuel quality and should not be considered to be scientifically

accurate.

Rough Idle and/ 
or Hesitation 
Under Hard 
Acceleration

1.

Substandard fuel.

1.

Drain and replace the fuel.

2.

Air leak in fuel line or injector.

2.

Locate and correct the leak. 

3.

Fuel filter cap or tank vent restriction.

3.

Replace the cap or the vent hose as required.

4.

Injector fault.

4.

Locate and replace the faulty injector.

5.

Intake manifold leak.

5.

Replace the manifold or the gaskets as needed.

 Fuel System Driveability Symptoms  (Continued)

PROBLEM

POTENTIAL CAUSE

CORRECTION

3-8 Fuel, Emissions, and Exhaust

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1.

Drain the fuel filter housing as follows:

• Stop the engine.

• Place a container under the drain valve hose, at the left front side of vehicle behind the driver side wheel.

• Open the drain valve.

• You may need to pump the plunger on the top of the fuel manager repeatedly.

• Fill a 1-liter (0.946 quart) container with a sample of the clean fuel.

• Close the drain valve.

NOTE:

Visually inspect the fuel sample for obvious contaminants such as water or sediment. Check the odor of the sample for the

presence of gasoline or other foreign solvents before testing for specific gravity.

2.

Fill the hydrometer tool J–38641-B with a fuel sample as follows:

• Squeeze the hydrometer bulb

• Immerse the hydrometer tip in the fuel sample

• Release the bulb and allow the fuel to enter the glass tube until the indicator floats freely.

• Gently spin the hydrometer to relieve the surface tension of the fuel sample.

3.

Read the scale on the glass bulb at the point where the top of the fuel sample contacts it:

• Reading this scale will indicate an approximate fuel oil specific gravity.

• Refer to the tool instructions on how to determine the API specific gravity.

• Refer to the Fuel Oil Specific Gravity Requirements table.

4.

If the correct fuel is being used in the conditions listed in Fuel Quality (below) and meets the fuel oil specific gravity
requirements for Diesel No. 1 or Diesel No. 2, the fuel is OK. If not, the fuel should be replaced.

5.

Prime the fuel system before starting the engine.

Fuel Oil Specific Gravity Requirements:

FUEL SYSTEM COMPONENTS

Mass Air Flow/ Air Intake Temp Sensor

The mass air flow sensor is used to measure the volume of air flow to the engine. The sensor measures mass flow rate by measuring
the rate of heat lost from a tiny micro machined silicon heater/thermometer held in the air stream. The greater the rate of heat loss,
the greater the air flow.

The sensor outputs are used by the engine control system to provide a faster turbo “spool-up” and crisper throttle response. In
addition, low-end power is stronger and the entire power band is much smoother.

Diesel No. 2

Diesel No. 1

Special

Tool

API

Gravity

30-39

39-44

J–38641–B

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 Fuel, Emissions, and Exhaust  3-9

Figure 3-2:   Mass Air Flow Sensor Circuit

MAF Sensor/Air Intake Temp Sensor Replacement

Removal

1.

Disconnect the electrical connector from the sensor (Figure 3-3).

2.

Remove the two screws securing the sensor and remove the sensor from the air intake tube.