Oshkosh JLG 400S, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3-114 – JLG Lift – 3120895
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 exhaust gas oxygen sensor
(HEGO) mounted in the exhaust system sends a voltage
signal to the controller. The controller then calculates any
correction that may need to be made to the air fuel ratio.
The controller then outputs signals to the EPR to correct
the amount of fuel being 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 the Platform Control Sta-
tion. Malfunctions in the system are identified by a Diag-
nostic Code number. In addition to notifying the operator
of the malfunction in the system the controller also stores
the information about the malfunction 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 is used to measure the
amount of oxygen present in the exhaust stream and com-
municate 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 dur-
ing 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 pres-
ent 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.
THE HEATED EXHAUST GAS OXYGEN SENSOR IS AN EMISSION
CONTROL DEVICE. IF THE HEGO FAILS TO OPERATE, REPLACE IT
WITH AN OEM REPLACEMENT PART. THE HEGO SENSOR IS SEN-
SITIVE 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 3-71. LPG Engine Control Unit (ECM)
Figure 3-72. ECM Assembly
Figure 3-73. Heated Exhaust Gas Oxygen Sensor
(HEGO)