JLG 660SJ Service Manual - Manual (Page 117)

SECTION 3 - CHASSIS & TURNTABLE
3121202 – JLG Lift – 3-67
FUEL PRESSURE REGULATOR
The fuel pressure regulator is a relief valve mounted in the
fuel filter. It provides a constant fuel pressure of 441 kPa
(64 psi).
If the pressure is too low, poor performance and a DTC 32
will set. If the pressure is too high, excessive odor and/or a
DTC 42 will result.
When replacing the fuel filter, be sure to use an identical
filter/regulator assembly. A standard fuel filter does not
regulate pressure and could cause engine problems or
component damage.
FUEL PUMP ELECTRICAL CIRCUIT
When the key is first turned "ON," the ECM energizes the
fuel pump relay for two seconds to build up the fuel pres-
sure quickly. If the engine is not started within two sec-
onds, the ECM/EPM shuts the fuel pump off and waits
until the engine is cranked. When the engine is cranked
and crankshaft position signal has been detected by the
SECM, the ECM/EPM supplies 12 volts to the fuel pump
relay to energize the electric fuel pump.
An inoperative fuel pump will cause a "no-start" condition.
A fuel pump which does not provide enough pressure will
result in poor performance.
FUEL RAIL
The fuel rail is mounted to the top of the engine and dis-
tributes fuel to the individual injectors. Fuel is delivered to
the fuel inlet tube of the fuel rail by the fuel lines.
ELECTRONIC GOVERNOR AND THROTTLE
BODY
In the 2.5L EFI industrial engine, throttle control is
achieved by using an electronic governor which is con-
trolled by the engine control module (ECM).
The electronic governor consists of a throttle body, an
electronically-actuated throttle plate, and a built-in throttle
position (TP) sensor. There are two pigtails that exit the
governor body. The 3-wire pigtail connects the TP sensor
to the ECM/EPM. Refer to "Throttle Position (TP) Sensor"
for more information.
The 2-wire pigtail carries the throttle signal from the ECM
to the governor. Desired engine speeds are stored in the
configuration program for each specific application, and
can be changed with the ECM/EPM calibration software.
When an engine speed is selected with the toggle switch,
the ECM/EPM sends the appropriate signal to the gover-
nor. This is a pulse-width modulated (PWM) signal which
cannot be read with conventional diagnostic tools such as
a voltmeter. A 12-volt signal is pulsed on and off at a high
rate of speed. The width of the "on" pulse determines the
amount of throttle opening. The ECM sends a signal with
the appropriate pulse width to the governor based on the
operator's choice of switch settings.
The electronic governor also acts as an idle air control
(IAC) valve. Changes in engine load are detected by the
ECM/EPM by comparing manifold absolute pressure
(MAP) with throttle position. When the ECM/EPM detects
a change in engine load, it can adjust idle speed by
changing the PWM signal to the governor.