Hummer H2. Manual — part 1482

arm indicates the fuel level. The fuel level sensor contains a variable resistor, which changes resistance in
correspondence to the amount of fuel in the fuel tank. The powertrain control module (PCM) sends the fuel
level information via the class 2 circuit to the instrument panel (I/P) cluster. This information is used for the I/P
fuel gauge and the low fuel warning indicator, if applicable. The PCM also monitors the fuel level input for
various diagnostics.

Fuel Pump

The fuel pump is mounted in the fuel sender assembly reservoir. The fuel pump is an electric high pressure
pump. Fuel is pumped to the fuel rail at a specified flow and pressure. The fuel pump delivers a constant flow of
fuel to the engine during low fuel conditions and aggressive vehicle maneuvers. The powertrain control module
(PCM) controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe acts to
dampen the fuel pulses and noise generated by the fuel pump.

Fuel Strainer

The fuel strainer attaches to the lower end of the fuel sender. The fuel strainer is made of woven plastic. The
functions of the fuel strainer are to filter contaminants and to wick fuel. Fuel stoppage at this point indicates that
the fuel tank contains an abnormal amount of sediment.

Fuel Filter

The fuel filter is contained in the fuel sender assembly inside the fuel tank. the paper filter element of the fuel
filter traps particles in the fuel that may damage the fuel injection system. The fuel filter housing is made to
withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There is no
service interval for fuel filter replacement.

Nylon Fuel Pipes

Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and
changes in temperature. There are 3 sizes of nylon pipes used: 9.5 mm (3/8 in) ID for the fuel supply, 7.6 mm
(5/16 in) ID for the fuel return, and 12.7 mm (1/2 in) ID for the vent. Heat resistant rubber hose or corrugated
plastic conduit protects the sections of the pipes that are exposed to chafing, to high temperatures, or to
vibration.

Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if
nylon fuel pipes are forced into sharp bends, the pipes kink and restrict the fuel flow. Also, once exposed to
fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Take special care when working
on a vehicle with nylon fuel pipes.

Quick-Connect Fittings

Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The
fittings consist of a unique female connector and a compatible male pipe end. O-rings, located inside the female

CAUTION: Refer to Fuel and EVAP Pipe Caution in Cautions and Notices.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2

connector, provide the fuel seal. Integral locking tabs inside the female connector hold the fittings together.

On-Board Refueling Vapor Recovery System (ORVR)

The On-Board Refueling Vapor Recovery System (ORVR) is an on-board vehicle system designed to recover
fuel vapors during the vehicle refueling operation. The flow of liquid fuel down the fuel filler pipe provides a
liquid seal which prevents vapor from leaving the fuel filler pipe. An EVAP pipe transports the fuel vapor to the
EVAP canister for use by the engine.

Fuel Pipe O-Rings

O-rings seal the threaded connections in the fuel system. Fuel system O-ring seals are made of special material.
Service the O-ring seals with the correct service part.

Fuel Rail Assembly

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2

Fig. 197: Injectors & Fuel Dampener
Courtesy of GENERAL MOTORS CORP.

The fuel rail assembly attaches to the engine intake manifold. The fuel rail assembly performs the following
functions:

z

Positions the injectors (3) in the intake manifold

z

Distributes fuel evenly to the injectors

z

Integrates the fuel dampener (2) into the fuel metering system

Fuel Injectors

The fuel injector assembly is a solenoid device controlled by the PCM that meters pressurized fuel to a single
engine cylinder. The PCM energizes the injector solenoid to open a normally closed ball valve. This allows the
fuel to flow into the top of the injector, past the ball valve, and through a director plate at the injector outlet. The
director plate has machined holes that control the fuel flow, generating a spray of finely atomized fuel at the
injector tip. Fuel from the injector tip is directed at the intake valve, causing the fuel to become further atomized
and vaporized before entering the combustion chamber. This fine atomization improves fuel economy and
emissions.

Fuel Pressure Regulator

The fuel pressure regulator is contained in the left fuel sender assembly.

Fuel Metering Modes of Operation

The PCM monitors voltages from several sensors in order to determine how much fuel to give the engine. The
PCM controls the amount of fuel delivered to the engine by changing the fuel injector pulse width. The fuel is
delivered under one of several modes.

Starting Mode

When the ignition is first turned ON, the PCM energizes the fuel pump relay for 2 seconds. This allows the fuel
pump to build pressure in the fuel system. The PCM calculates the air/fuel ratio based on inputs from the engine
coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP)
sensors. The system stays in starting mode until the engine speed reaches a predetermined RPM.

Clear Flood Mode

If the engine floods, clear the engine by pressing the accelerator pedal down to the floor and then crank the
engine. When the TP sensor is at wide open throttle (WOT), the PCM reduces the fuel injector pulse width in
order to increase the air to fuel ratio. The PCM holds this injector rate as long as the throttle stays wide open
and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the PCM returns to
the starting mode.

Run Mode

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the
engine speed is above a predetermined RPM, the system begins Open Loop operation. The PCM ignores the
signal from the heated oxygen sensors (HO2S). The PCM calculates the air/fuel ratio based on inputs from the
ECT, MAF, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions:

z

Both front HO2S have varying voltage output, showing that both HO2S are hot enough to operate
properly.

z

The ECT sensor is above a specified temperature.

z

A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for each different engine, and are stored in the electrically
erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after
reaching these values. In Closed Loop, the PCM calculates the air/fuel ratio, injector ON time, based upon the
signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to
14.7:1.

Acceleration Mode

When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly. To prevent
possible hesitation, the PCM increases the pulse width to the injectors to provide extra fuel during acceleration.
This is also known as power enrichment. The PCM determines the amount of fuel required based upon the TP,
the ECT, the MAP, the MAF, and the engine speed.

Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The PCM monitors the
corresponding changes in the TP, the MAP, and the MAF. The PCM shuts OFF fuel completely if the
deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in
order to prevent damage to the catalytic converters.

Battery Voltage Correction Mode

When the battery voltage is low, the PCM compensates for the weak spark delivered by the ignition system in
the following ways:

z

Increasing the amount of fuel delivered

z

Increasing the idle RPM

z

Increasing the ignition dwell time

Fuel Cutoff Mode

The PCM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the
powertrain from damage and improve driveability:

z

The ignition is OFF. This prevents engine run-on.

z

The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2