JLG 660SJ Service Manual - Manual (Page 152)

SECTION 3 - CHASSIS & TURNTABLE
3-102 – JLG Lift – 3121202
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.
Gasoline Fuel Pump
The Gasoline is stored as a liquid in the fuel tank and in
drawn into the fuel system by an electric fuel pump. The
fuel pump will receive a signal from the ECM to prime the
fuel system for approximately 2 seconds prior to start.
Priming of the fuel system provides for a quicker start,
when the engine begins to crank.
Gasoline Pressure And Temperature Sensor
Manifold
This engine is equipped with a fuel injector rail that does
not have a pressure regulator or a return circuit to the fuel
tank. Fuel pressure for this engine is regulated by the
engine’s ECM. The ECM receive fuel pressure and tem-
perature feedback from the gasoline fuel sensor manifold
and uses this information to control the ground side of the
fuel pump. Fuel pressure is regulated by the ECM pulse
width modulating (PWM) the fuel pump. The fuel pressure
and temperature sensor manifold has a return or "bleed"
circuit that connects back to the fuel tank. This circuit is
used to bleed off any vapor that develops in the line and
return a small amount of fuel to the tank. The fuel comes
from the fuel tank and passes through the fuel pump. Fuel
exits the fuel pump, passes through the filter and then
enters the fuel pressure and temperature manifold assem-
bly. Fuel flows through the feed circuit and is delivered to
the fuel injector rail. Fuel that enters the bleed circuits
through they bypass valve in the manifold is returned to
the fuel tank.
Figure 3-82. Heated Exhaust Gas Oxygen Sensor
(HEGO)
Figure 3-83. Gasoline Fuel Pressure and Temperature
Manifold Assembly