Ford Explorer, Maintaince And Repair Manual, Page: 537 / 1119

ELECTRONIC ENGINE CONTROLS
Electronic Engine Control (EEC)
All Sequential Fuel Injection (SFI) systems use the EEC system. The heart of the EEC system is a
micro−processor called the Powertrain Control Module (PCM). The PCM receives data from a number of
sensors and other electronic components (switches, relay, etc.). Based on information received and
information programmed in the PCM's memory, it generates output signals to control various relay, solenoids
and other actuators. The PCM in the EEC system has calibration modules located inside the assembly that
contain calibration specifications for optimizing emissions, fuel economy and drive ability. The calibration
module is called a PROM.
The following are the electronic engine controls used by 1991−99 Ranger/Explorer and Mountaineers:
Powertrain Control Module (PCM) •
Throttle Position (TP) sensor •
Mass Air Flow (MAF) sensor •
Intake Air Temperature (IAT) sensor •
Idle Air Control (IAC) valve •
Engine Coolant Temperature (ECT) sensor •
Heated Oxygen Sensor (HO2S)
•
Camshaft Position (CMP) sensor •
Knock Sensor (KS) •
Vehicle Speed Sensor (VSS) •
Crankshaft Position (CKP) sensor •
The MAF sensor (a potentiometer) senses the position of the airflow in the engine's air induction system and
generates a voltage signal that varies with the amount of air drawn into the engine. The IAT sensor (a sensor
in the area of the MAF sensor) measures the temperature of the incoming air and transmits a corresponding
electrical signal. Another temperature sensor (the ECT sensor) inserted in the engine coolant tells if the engine
is cold or warmed up. The TP sensor, a switch that senses throttle plate position, produces electrical signals
that tell the PCM when the throttle is closed or wide open. A special probe (the HO2S) in the exhaust
manifold measures the amount of oxygen in the exhaust gas, which is in indication of combustion efficiency,
and sends a signal to the PCM. The sixth signal, camshaft position information, is transmitted by the CMP
sensor, installed in place of the distributor (engines with distributorless ignition), or integral with the
distributor.
The EEC microcomputer circuit processes the input signals and produces output control signals to the fuel
injectors to regulate fuel discharged to the injectors. It also adjusts ignition spark timing to provide the best
balance between driveability and economy, and controls the IAC valve to maintain the proper idle speed.
Because of the complicated nature of the Ford system, special tools and procedures are necessary for
testing and troubleshooting.
Powertrain Control Module (PCM)
OPERATION
The Powertrain Control Module (PCM) performs many functions on your car. The module accepts
information from various engine sensors and computes the required fuel flow rate necessary to maintain the
ELECTRONIC ENGINE CONTROLS 533