Engine management system - MEMS (Description): Description and operation

Description

General

The Modular Engine Management System Version 3 (MEMS 3) is a sequential, multiport fuel injection system controlled by the Engine Control Module (ECM).

The ECM controls the operation of the fuel system, ignition system, evaporative emission control, cooling system and the air conditioning system.

The ECM uses the speed/density method of air flow measurement to calculate fuel delivery. This method calculates the density of the intake air by measuring its pressure and temperature.

The density signal, combined with the engine speed signal, allows the ECM to make a calculation of the air volume being inducted and determine the quantity of fuel to be injected to give the correct air/fuel ratio.

MEMS 3 is designed to meet new exhaust emission standard; ECD 3 (European Commission Directive Stage 3), also known as OBD (On-Board Diagnostics).

Engine Control Module

The ECM is located in the Environmental box (E-box) on the left hand side of the engine compartment. The ECM is accessible by loosening five cap screws to release the lid on the box.

The E-box is a lidded container that provides a protected environment for the ECM and the EAT ECU. An open hub, centrifugal fan powered by an electric motor ventilates the E-box with air from the passenger compartment. Exhaust air from the E-box is directed back into the passenger compartment. The ventilating and exhaust air is routed between the passenger compartment and the E-box through plastic ducting and corrugated rubber hoses. Operation of the cooling fan is controlled by a thermostatic switch in the E-box. The thermostatic switch receives a power feed while the ignition switch is in position II. If the temperature in the E-box reaches 35 °C (95 °F) the thermostatic switch closes and connects the power feed to the fan, which runs to cool the E-box with air from the passenger compartment. When the temperature in the E-box decreases to 27 °C (80 °F), the thermostatic switch opens and stops the fan. To prevent the fan seizing up in colder climates, where it may not operate for long periods of time, the fan also receives a power feed from the starter circuit so that it runs each time while the engine is cranked.

The ECM electronic components are housed in an aluminium case for heat dissipation and protection from electromagnetic interference.