All vehicles covered in this guide are utilize an electronic multi-port fuel injection system. The heart of this system is a micro-processor called the Powertrain Control Module (PCM) or Electronic Control Module (ECM). The PCM/ECM receives data from a number of sensors and other electronic components (switches, relay, etc.). Based on information received and information programmed in the PCM/ECM's memory, it generates output signals to control various relay, solenoids and other actuators. The PCM/ECM in this system has calibration modules located inside the assembly that contain calibration specifications for optimizing emissions, fuel economy and driveability. The calibration module is called a PROM.
The following are the electronic engine controls used by MPV, Navajo and B Series Pick-ups:
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 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 this system, special tools and procedures are necessary for testing and troubleshooting.