JLG 450A_AJ Series II Service Manual - Manual (Page 124)

SECTION 3 - CHASSIS & TURNTABLE
3-84 – JLG Lift – 3121290
Direct Electronic Pressure Regulator (DEPR)
THE DEPR IS AN EMISSION CONTROL DEVICE AND SHOULD ONLY BE SERVICED
BY QUALIFIED TECHNICIANS.
The ECI engine management system uses the DEPR to control
fuel delivery for precise fuel metering needed for optimum
combustion, fuel economy, and transient response.
The DEPR is a single-stage microprocessor based electrome-
chanical fuel pressure regulator that incorporates a high
speed/fast acting actuator. It communicates with the Engine
Control Module (ECM) over a Controller Area Network (CAN)
link, receiving fuel pressure commands and broadcasting
DEPR operating parameters back to the ECM.
The DEPR can regulate fuel pressure from -18 to +13 inches of
water column above the Mixer air inlet pressure, providing suf-
ficient control authority to stall an engine either rich or lean.
When the DEPR receives an output pressure command from
the ECM, the valve is internally driven to attain targeted fuel
pressure, the DEPR then closes the loop internally using a built
in fuel pressure sensor to maintain target fuel pressure/fuel
flow rate, until another external command from the ECM is
received (intervals < 10 ms).
The DEPR has an integral fuel temperature sensor that is used
by the ECM to correct for variations in fuel density. This pro-
vides an extremely accurate method for open loop fuel con-
trol. Then with the addition of the pre- and post-cat oxygen
sensors, the pressure command transmitted form the ECM can
be further adjusted using closed loop feedback.
Figure 3-60. Direct Electronic Pressure Regulator
Air Fuel Mixer
THE AIR/FUEL MIXER IS AN EMISSION CONTROL DEVICE. COMPONENTS INSIDE
THE MIXER ARE SPECIFICALLY CALIBRATED TO MEET THE ENGINE’S EMIS-
SIONS REQUIREMENTS AND SHOULD NEVER BE DISASSEMBLED OR REBUILT.
IF THE MIXER FAILS TO FUNCTION CORRECTLY, REPLACE WITH AN OEM
REPLACEMENT PART.
The air valve mixer is a self-contained air-fuel metering device.
The mixer is an air valve design, utilizing a relatively constant
pressure drop to draw fuel into the mixer from cranking
speeds 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, and negative pressure
begins to build. This negative pressure signal is communicated
to the top of the air valve chamber through vacuum ports in
the air valve assembly. A pressure/force imbalance begins to
build across the air valve diaphragm between the air valve
vacuum chamber and the atmospheric pressure below the
diaphragm.
The vacuum being created is referred to as Air Valve Vacuum
(AVV). As the air valve vacuum reaches the imbalance point,
the air valve begins to lift against the air valve spring. The
amount of AVV generated is a direct result of throttle position.
At low engine speed the air valve vacuum and the air valve
position is low, creating a small venturi for the fuel to flow. As
engine speed increases, AVV increases and the air valve is
lifted higher creating a much larger venturi. Air valve vacuum
is communicated from the mixer venturi to the IEPR via the
fuel supply hose.
Figure 3-61. Air Fuel Mixer