JLG 450A_AJ Series II Service Manual - Manual (Page 175)

SECTION 3 - CHASSIS & TURNTABLE
3121180 – JLG Lift – 3-125
Engine Control Module
To obtain maximum effect from the catalyst and accurate
control of the air fuel ratio the emission certified engine is
equipped with an onboard computer or Engine Control
Unit (ECM). The ECM is a 32 bit controller which receives
input data from sensors fitted to the engine and fuel sys-
tem and then outputs various signals to control engine
operation.
One specific function of the controller is to maintain
“closed loop fuel control”. Closed loop fuel control is
accomplished when the Hot Exhaust Gas Oxygen sensor
(HEGO) mounted in the exhaust system sends a voltage
signal to the controller. The controller calculates correc-
tions needed for the air fuel ratio. The controller then out-
puts signals to the EPR to correct amount of fuel supplied
to the mixer. At the same time, the ECM may correct the
throttle blade position to correct speed and load of the
engine.
The controller also performs diagnostic functions on the
fuel system and notifies the operator of malfunctions by
turning on a Malfunction Indicator Light (MIL) mounted in
the Ground Control Station and Platform Control Station.
Malfunctions in the system are identified by a Diagnostic
Code number. In addition to notifying the operator of a
system malfunction the controller also stores malfunction
information in its memory.
Heated Exhaust Gas Oxygen Sensor
There are two Heated Exhaust Gas Oxygen Sensors
(HEGO). The first HEGO is mounted in the exhaust system
downstream of the engine. It measures the amount of oxy-
gen present in the exhaust stream and communicate that
to the ECM via an electrical signal. The amount of oxygen
present in the exhaust stream indicates whether the fuel/
air ratio is too rich or too lean. If the HEGO sensor signal
indicates that the exhaust stream is too rich the ECM will
decrease or lean the fuel mixture during engine operation,
if the mixture is too lean the ECM will richen the mixture.
The ECM continuously monitors the HEGO sensor output.
If a rich or lean condition is present for an extended period
of time, and the ECM cannot correct the condition, the
ECM will set a diagnostic code and turn on the MIL light in
control box.
The second HEGO is mounted in the exhaust system after
the muffler. It measures the amount of oxygen in the
exhaust system after the catalyst treatment has been com-
pleted in the muffler. If the ECM detects that the catalytic
action in the muffler is not sufficient and fuel correction
cannot correct the malfunction the MIL light is illuminated
in the control box and a DTC code will stored in the com-
puter.
HEATED EXHAUST GAS OXYGEN SENSOR IS AN EMISSION CON-
TROL DEVICE. IF THE HEGO FAILS TO OPERATE, REPLACE IT
WITH AN OEM REPLACEMENT PART. HEGO SENSOR IS SENSI-
TIVE TO SILICONE OR SILICONE BASED PRODUCTS AND CAN
BECOME CONTAMINATED. AVOID USING SILICONE SEALERS OR
HOSES TREATED WITH SILICONE LUBRICANTS IN THE AIR
STREAM OR FUEL LINES.
Gasoline Multi Point Fuel Injection System
(MPFI)
The primary components of the Gasoline Multi Point Fuel
Injection (MPFI) fuel system are the fuel tank, electric fuel
pump, fuel pressure and temperature sensor manifold,
fuel filter, and fuel rail.
Figure 3-82. LPG Engine Control Unit (ECM)
Figure 3-83. ECM Assembly
Figure 3-84. Heated Exhaust Gas Oxygen Sensor
(HEGO)