JLG 740AJ Service Manual - Manual (Page 154)

SECTION 3 - CHASSIS & TURNTABLE
3-102 – JLG Lift – 3121160
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSOR
The manifold absolute pressure (MAP) sensor responds
to changes in intake manifold pressure (vacuum). The
MAP sensor signal voltage to the Engine Module varies
from below 2 volts at idle (high vacuum) to above 4 volts
with the ignition ON, engine not running or at wide-open
throttle (low vacuum).
The MAP sensor is used to determine the following:
• Engine vacuum level for engine control purposes.
• Barometric pressure (BARO)
If the Engine Module detects a voltage that is significantly
lower than the estimated MAP value for 2 or more consec-
utive seconds, DTC 14 will be set. A signal voltage signifi-
cantly higher than the estimated MAP value for 2 or more
consecutive seconds will set DTC 24.
ENGINE CONTROL MODULE (ECM)/ENGINE
PERFORMANCE MODULE (EPM)
The engine will be controlled by one of two different
Engine Modules. The Ford EFI engine was originally
equipped with an ECM. The EPM was developed to
replace the ECM and provide enhanced performance and
durability. To see the physical difference between the ECM
and EPM, refer to Figure 3-55., ECM/EPM Identification.
The Engine Module controls the following:
• Fuel metering system
• Ignition timing
• On-board diagnostics for engine functions
The Engine Module constantly observes the information
from various sensors. The Engine Module controls the
systems that affect engine performance. The Engine Mod-
ule performs the diagnostic function of the system. It can
recognize operational problems, alert the operator
through the Malfunction Indicator Lamp (MIL), and store
diagnostic trouble codes (DTCs). DTCs identify the prob-
lem areas to aid the technician in making repairs.
The Engine Module supplies either 5 or 12 volts to power
various sensors or switches. The power is supplied
through resistances in the Engine Module which are so
low in value that a test light will not light when connected
to the circuit. In some cases, even an ordinary shop volt-
meter will not give an accurate reading because its resis-
tance is too low. Therefore, a digital voltmeter with at least
10 meg ohms input impedance is required to ensure
accurate voltage readings. The Engine Module controls
output circuits such as the fuel injectors, electronic gover-
nor, etc., by control ling the ground or the power feed cir-
cuit through transistors or other solid state devices.
The Engine Module is designed to maintain exhaust emis-
sion levels to government mandated standards while pro-
viding excellent operation and fuel efficiency. The Engine
Module monitors numerous engine functions via elec-
tronic sensors such as the throttle position (TP) sensor
and the heated oxygen sensor (HO2S).
ENGINE MODULE INPUTS/OUTPUTS
Inputs—Operating Conditions
• Engine Coolant Temperature
• Crankshaft Position
• Exhaust Oxygen Content
• Manifold Absolute Pressure
• Battery Voltage
• Throttle Position
• Fuel Pump Voltage
• Intake Air Temperature
• Camshaft Position
Outputs - System Controlled
• Fuel Control
• Idle Air Control
• Electric Fuel Pump
• Diagnostics:
- Malfunction Indicator Lamp
- Data Link Connector (DLC)