Fuel Injectors; Fuel Tanks, Lines, And Valves; Glow Plugs - Hummer H1 Service Manual

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.
FUEL
RETURN
PORT
INJECTOR
BODY
NOZZLE
Figure 3-6: Fuel Injector Components
FUEL
INLET
PORT
FUEL
RETURN
PORT
VALVE
SPRING
PINTLE
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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.
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