JLG 450A_AJ Series II Service Manual - Manual (Page 152)

SECTION 3 - CHASSIS & TURNTABLE
3-102 – JLG Lift – 3121180
3.14 CIRCUIT TESTING TOOLS
DO NOT USE A TEST LIGHT TO DIAGNOSE ENGINE ELECTRICAL
SYSTEMS UNLESS SPECIFICALLY INSTRUCTED. A TEST LIGHT
CAN PUT AN EXCESSIVE LOAD ON AN ECM CIRCUIT AND
CAUSE COMPONENT DAMAGE. ONLY USE A DIGITAL VOLTME-
TER WITH AN INPUT IMPEDANCE OF AT LEAST 10 MEGOHMS
FOR VOLTAGE MEASUREMENTS.
Electrostatic Discharge Damage
Electronic components used in the ECM are often
designed to carry very low voltage. Electronic compo-
nents are susceptible to damage caused by electrostatic
discharge. Less than 100 volts of static electricity can
cause damage to some electronic components. By com-
parison, It takes as much as 4000 volts for a person to feel
the spark of a static discharge.
There are several ways for a person to become statically
charged. The most common are friction and induction.
An example of charging by friction is a person sliding
across a seat.
Charge by induction occurs when a person with well-insu-
lated shoes stands near a highly charged object and
momentarily touches ground. Charges of the same polar-
ity are drained off, leaving the person highly charged with
the opposite polarity. Static charges can cause damage,
therefore it is important to-use care when handling and
testing electronic components.
Follow these guidelines to prevent possible electrostatic
discharge damage:
• Do not touch ECM connector pins or soldered compo-
nents on the ECM board.
• Do not open the replacement part package until the
part is ready to be installed.
• Before removing the part from the package, ground
package to a known good ground on equipment.
• If part has been handled while sliding across a seat,
while sitting down from a standing position, or while
walking a distance, touch a known good ground
before installing part.
Fuel System
FUEL INJECTOR
The Electronic Fuel Injection (EFI) fuel injector is a sole-
noid-operated device controlled by the ECM. The ECM
energizes the solenoid, which opens a valve to allow fuel
delivery.
Fuel is injected under pressure in a conical spray pattern
at opening of the intake valve. Excess fuel not used by
injectors passes through the fuel pressure regulator
before being returned to the fuel tank.
A fuel injector stuck partly open will cause loss of fuel pres-
sure after engine is shut down, causing long crank times.
FUEL METERING SYSTEM COMPONENTS
The fuel metering system is made up of the following
parts:
• Fuel injectors
• Fuel rail
• Fuel pressure regulator/filter assembly
• Electronic governor
• ECM
• Crankshaft position (CKP) sensor
• Camshaft position (CMP) sensor
• Fuel pump
• Fuel pump relay
BASIC SYSTEM OPERATION
The fuel metering system starts with fuel in the fuel tank.
Fuel is drawn to the fuel pump through a pre-filter. The
electric fuel pump then delivers fuel to the fuel rail through
an inline fuel filter. The pump is designed to provide fuel at
a pressure above pressure needed by the injectors. A fuel
pressure regulator in the fuel filter assembly keeps fuel
available to the fuel injectors at a constant pressure. A
return line delivers unused fuel back to the tank.