SECTION 3 - CHASSIS & TURNTABLE
3-152
3121160
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The manifold absolute pressure (MAP) sensor responds to
changes in intake manifold pressure (vacuum). The MAP sen-
sor 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 vac-
uum).
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 consecutive
seconds, DTC 14 will be set. A signal voltage significantly
higher than the estimated MAP value for 2 or more consecu-
tive 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 dif-
ference between the ECM and EPM, refer to Figure 3-78., 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 Module performs the
diagnostic function of the system. It can recognize operational
problems, alert the operator through the Malfunction Indica-
tor Lamp (MIL), and store diagnostic trouble codes (DTCs).
DTCs identify the problem areas to aid the technician in mak-
ing repairs.
The Engine Module supplies either 5 or 12 volts to power vari-
ous sensors or switches. The power is supplied through resis-
tances 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 voltmeter will not give an accu-
rate reading because its resistance is too low. Therefore, a digi-
tal 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, elec-
tronic governor, etc., by control ling the ground or the power
feed circuit through transistors or other solid state devices.
The Engine Module is designed to maintain exhaust emission
levels to government mandated standards while providing
excellent operation and fuel efficiency. The Engine Module
monitors numerous engine functions via electronic sensors
such as the throttle position (TP) sensor and the heated oxy-
gen 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)
Summary of Contents for 740AJ
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