Air Fuel Mixer; Electronic Throttle Control (Etc) - JLG 400S Service And Maintenance Manual

Air Fuel Mixer

The air valve mixer is an air-fuel metering device and is com-
pletely self-contained. The mixer is an air valve design, utiliz-
ing a relatively constant pressure drop to draw fuel into the
mixer from cranking to full load. The mixer is mounted in the
air stream ahead of the throttle control device.
When the engine begins to crank, it draws in air with the air
valve covering the inlet, negative pressure begins to build.
This negative pressure signal is communicated to the top of
the air valve chamber through 4 vacuum ports in the air valve
assembly. A pressure/force imbalance begins to build across
the air valve diaphragm between the air valve vacuum cham-
ber and the atmospheric pressure below the diaphragm. The
air valve vacuum spring is calibrated to generate from 4.0 in.
(101.6 mm) of water column at start to as high as 14.0 in.
(355.60 mm) of water column at full throttle. The vacuum
being created is referred to as Air Valve Vacuum (AVV). As the
air valve vacuum reaches 4.0 in. (101.6 mm) of water column,
the air valve begins to lift against the air valve spring. The
amount of AVV generated is a direct result of the throttle posi-
tion. At low engine speed the air valve vacuum is low and the
air valve position is low thus creating a small venturi for the
fuel to flow. As the engine speed increase the AVV increases
and the air valve is lifted higher thus creating a much larger
venturi. This air valve vacuum is communicated from the mixer
venture to the LPR secondary chamber via the low pressure
fuel supply hose. As the AVV increases in the secondary cham-
ber the secondary diaphragm is drawn further down forcing
the secondary valve lever to open wider.
Figure 3-107. Air Fuel Mixer
3121671
SECTION 3 - CHASSIS & TURNTABLE

Electronic Throttle Control (ETC)

Engine speed and load control is maintained by an ETC device.
Speed and load control are determined by the ECM. Defaults
programmed into the ECM software and throttle position sen-
sors allow the ECM to maintain safe operating control over the
engine. The Electronic Throttle Control device or "throttle
body assembly" is connected to the intake manifold of the
engine. The electronic throttle control device utilizes an elec-
tric motor connected to the throttle shaft. When the engine is
running electrical signals are sent from the equipment con-
trols to the engine ECM when the operator depresses an
equipment function switch. The ECM then sends an electrical
signal to the motor on the electronic throttle control to
increase or decrease the angle of the throttle blade thus
increasing or decreasing the air/fuel flow to the engine.
The electronic throttle control device also incorporates two
internal Throttle Position Sensors (TPS) which provide output
signals to the ECM as to the location of the throttle shaft and
blade. The TPS information is used by the ECM to correct
speed and load control as well as emission control.
Figure 3-108. ETC throttle control device
3-135