JLG 601S ANSI Service Manual - Manual (Page 125)

SECTION 3 - CHASSIS & TURNTABLE
3120746 – JLG Lift – 3-85
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 Engine Module ener-
gizes the fuel pump relay for two seconds to build up the
fuel pressure quickly. If the engine is not started within two
seconds, the Engine Module 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 Engine Module, the Engine Module 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 Module.
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 Engine Module. Refer to "Throttle Position (TP) Sen-
sor" for more information.
The 2-wire pigtail carries the throttle signal from the
Engine Module to the governor. Desired engine speeds
are stored in the configuration program for each specific
application, and can be changed with the Engine Module
calibration software. When an engine speed is selected
with the toggle switch, the Engine Module sends the
appropriate signal to the governor. This is a pulse-width
modulated (PWM) signal which cannot be read with con-
ventional 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 Engine Module sends a signal with the
appropriate pulse width to the governor based on the
operator's choice of switch settings.