Hummer H1 (2002+). Manual - part 35

The fuel lift pump is located on the firewall near the drivers
side of the engine. The electric fuel lift pump has a hollow
plunger that slides in a bore located in the center passage be-
tween the inlet and outlet ports (Figure 3-2). An inlet valve is
mounted on one end of the hollow plunger, and an outlet valve
is positioned at the outlet end of the center passage. Both
valves are closed by spring force.

The lift pump is designed to move fuel under a low (suction)
pressure from the fuel tank and deliver it through the filter to
the transfer pump, inside the fuel injection pump. To operate
correctly, the injection pump must have fuel at the correct pres-
sure and without air bubbles.

The lift pump is checked as part of the fuel supply system diag-
nosis. The lift pump should deliver fuel with a minimum vol-
ume of one half pint (0.24 liter) in 15 seconds and tee'd in at
the injection pump fuel inlet connection running at idle, with a
pressure of 5.8 to 8.7 psi (40 to 60 kPa). The lift pump suction
line from the fuel tank must be air tight for correct operation of
the injection pump.

Any air present in the fuel system will

cause runability problems and possible diagnostic trouble
codes (DTCs) to be set in PCM memory.

Figure 3-2: Fuel Lift Pump Construction

The electrical circuit for the lift pump involves several main
components (Figure 3-3). A relay mounted in the exterior fuse
box, and the lift pump itself, mounted near the filter on the left
side of the engine compartment.

When the driver moves the ignition switch to the “RUN” posi-
tion, the lift pump relay is energized by the PCM for 5 to 20
sec., depending on PCM time out.

As soon as the PCM receives RPM signals from the EFI pump
the relay is energized again. The lift pump remains running as
long as the engine runs.

Figure 3-3: Fuel Lift Pump Electrical Circuit

FUEL

INJECTION

PUMP

INJECTORS

TANK SELECTOR

MAIN

TANK

AUXILIARY

TANK

FUEL

LINES

ELECTRIC

FUEL

LIFT

PUMP

FUEL

FILTER/
WATER

SEPARATOR

FUSE 2D
20A
INTERIOR

FUEL PUMP
RELAY
EXTERIOR
FUSE BOX

C1-10

POWERTRAIN

CONTROL

MODULE

FUEL PUMP

RELAY CONTROL

FUEL LIFT
PUMP SIGNAL

TO FUEL

SELECTOR SWITCH

FUEL
LIFT
PUMP

57 BK

787 GY

C27-D5

57 BK

C27-D8

238 DG

537 OR

9-S12-051

____________________________________________

Fuel, Emissions, and Exhaust 3-3

5745159

Fuel Filter-Water Separator

The filter-water separator is located at the driver side of the en-
gine compartment firewall (Figure 3-4). It performs five func-
tions which are:

• Fuel filtering (2-stage)

• Water separation

• Water detection

• Water drain

• Fuel heater

Fuel filtering and water separation is through a 2-stage, re-
placeable filter element. The filter second stage causes water to
separate from the fuel in the form of droplets. These droplets
are collected in a reservoir at the bottom of the filter element
housing. Water is then drained off through a drain valve and
hose. The drain valve is located in the driver side wheel well.

Water detection and fuel heating are controlled by sensors in
the filter housing. Water build-up causes the water sensor to
activate the instrument panel “drain filter” warning light. Fuel
heating occurs during cold ambient temperatures. It is con-
trolled by a sensor in the fuel inlet port that monitors incoming
fuel temperature. When temperature falls to a point where wax
build-up could occur, the sensor activates the heat element
within the filter housing. The heater will continue to operate
until incoming fuel temperature is at or above 46° F (8° C).

Figure 3-4: Fuel Filter Breakdown

Electronic Injection Pump

The turbo diesel injection pump (Figure 3-5) is controlled by
the powertrain control module based on inputs from the elec-
tronic accelerator pedal and various engine sensors.

The drive mechanism for the pump consists of a drive gear on
the camshaft, and a driven gear on the pump. The pump is op-
erated at camshaft speed in the opposite direction of rotation.

A rotary type pump mechanism pressurizes fuel to the injec-
tors. Pressure at the injector nozzles is approximately 2000 psi
(138 bar). Residual pressure in the injector lines is maintained
at 500 psi (3447 kPa) during operation.

Fuel distribution to individual nozzles occurs at the pump head
and rotor assembly and is activated by the fuel solenoid driver.
High strength, plated steel lines are used to connect each injec-
tor to the pump.

The powertrain control module controls injection timing and
fuel mixture according to input signals from various sensors.

A crankshaft position sensor and optical sensors are used to
provide engine and injection pump position and speed signals.
These signals are transmitted to the PCM and used as reference
for fuel flow and timing.

The injection pump is equipped with a shut off solenoid con-
trolled by the PCM. The purpose of the solenoid, is to close and
stop fuel flow within the pump. This occurs when the ignition
switch is moved to the “Off” position. At this point, loss of PCM
hold-open voltage de-energizes the solenoid causing it to close.

Figure 3-5: Electronic Fuel Injection Pump

AIR BLEED

VALVE

RETAINING

NUT

FILTER

HOUSING

SPRING

SEAL

HEATER

SCREEN

O-RING

SENSOR

ELEMENT

SOLENOID

DRIVER

FUEL

SOLENOID

PUMP

SHAFT

SHUT-OFF

SOLENOID

OPTICAL/FUEL

TEMPERATURE

SENSOR

INJECTION TIMING

STEPPER MOTOR

3-4

Fuel, Emissions, and Exhaust

_____________________________________________

Fuel Injectors

An identical fuel injector nozzle is used for each cylinder. The
nozzle is threaded into the cylinder head and positioned so the
injector nozzle extends into the combustion prechamber.

The injectors are a spring loaded, valve and pintle design
(Figure 3-6). The pintle forms the injector nozzle and the valve
seats in the nozzle tip opening.

Fuel is supplied to each nozzle and in the necessary sequence,
by the fuel injection pump. The high pressure fuel pulse over-
comes spring pressure lifting the valve off its seat. Pressurized
fuel then enters the prechamber through the nozzle in the form
of a highly atomized spray.

A small amount of fuel travels around the nozzle and valve for lu-
brication purposes. This fuel cycles back to the fuel return system
through the fuel return ports at the upper end of each nozzle.

The fuel injection nozzles are not repairable and are serviced
only as an assembly. However, they may be cleaned to remove
contamination.

Figure 3-6: Fuel Injector Components

Fuel Tanks, Lines, and Valves

The main and auxiliary fuel tanks are made of high density
polyethylene. Auxiliary fuel tank capacity is 17 gallons (64.3
liters). Main tank capacity is 25 gallons (94.6 liters).

Quick connect fittings are used at most of the fuel line connec-
tion points.

Fuel level transmitters for main and auxiliary tanks are
mounted within the tanks. A selector valve, mounted on the
passenger side of the frame, controls tank flow and selection.

A check valve is used in the supply and return lines to prevent
backflow. Vent lines are used at both tanks to avoid internal
pressure buildup.

Fuel return lines are used to send unused fuel from the nozzles
and the injection pump back to the fuel tanks.

Glow Plugs

The diesel engine glow plugs are threaded into the cylinder
head and extend into the combustion prechamber. The purpose
of the plugs is to heat air entering the combustion chambers to
help start the combustion process when the engine is cold.

The glow plugs are used as an aid to starting; especially when
ambient temperatures are low. The plugs are cycled on/off for
short time periods prior to engine cranking and during initial
start-up. The plugs are not on continuously, as plug damage
can occur after 6-7 seconds.

Turbo diesel engines use a glow plug relay that is controlled by
the PCM based on inputs from engine temperature sensors.
The glow plugs will cycle after the engine has started to main-
tain good combustion.

Electronic Accelerator Pedal

Turbo diesel models are equipped with an electronic accelera-
tor pedal assembly (Figure 3-7). The assembly consists of a
pedal and arm, mounting bracket, and potentiometer module.
The pedal assembly mounts in a conventional location.

The pedal potentiometer module contains three potentiometers
that send varying voltage signals to the PCM. By comparing
the different voltage signals against a standard, the PCM can
determine fuel delivery rate based on accelerator pedal posi-
tion.

A “check throttle” warning light is used to alert the driver of a
problem with the pedal assembly.

Some faults in the pedal potentiometer module or related wir-
ing will trigger the check throttle warning light. The light is lo-
cated in the status center. Some faults will cause loss of cruise
control only and multiple faults in the APP circuit can result in
decreased performance or engine idle only.

FUEL

RETURN

PORT

INJECTOR

BODY

NOZZLE

PINTLE

VALVE

SPRING

FUEL

RETURN

PORT

FUEL

INLET

PORT

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