Modular engine management system operation

MODULAR ENGINE MANAGEMENT SYSTEM OPERATION

The Modular Engine Management System (MEMS) is a combined engine management system using a single Engine Control Module to control the multipoint fuel injection, idle speed control and ignition systems.

Electronic Control Module (ECM)

The ECM processes all inputs and outputs related to the operation of the fuel injection and ignition systems. The ECM is located on a mounting plate behind the battery in the engine compartment. The ECM comprises an aluminium cast body with a pressed alloy sealed lid. A socket is positioned on it’s side face and receives a multiplug from the engine wiring harness. The socket contains 36 pins, although only the pins corresponding to those in the multiplug are used.

The multiplug is connected to the engine wiring harness to each individual sensor. The multiplug fits into the corresponding socket on the side face of the ECM and is locked in position with a plastic clip. A rubber seal within the body of the multiplug prevents the ingress of moisture. The ECM harness multiplug incorporates plated pins to minimise oxidation and give improved reliability.

The ECM monitors the conditions required for optimum combustion of fuel in the cylinder through sensors located at strategic points around the engine. From these sensor inputs, the engine control module can adjust the fuel quantity and timing of the fuel being delivered to the cylinders.

The main features are as follows:

• A single ECM controls the fuel injection system and the ignition system. The ECM incorporates short circuit protection and can store intermittent faults on certain inputs. TestBook can interrogate the ECM for these stored faults.
• In conjunction with the Throttle Position (TP) sensor, the ECM uses the speed/density method of air flow measurement to calculate fuel delivery. This method measures the crankshaft position/speed, inlet air temperature and inlet manifold pressure and assumes that the engine is a calibrated vacuum pump, with its characteristics stored in the ECM, it can then determine the correct amount of fuel to be injected.
• The ECM contains an integral Manifold Absolute Pressure (MAP) sensor. The MAP sensor reads manifold pressure via a hose connected to the inlet manifold. The manifold pressure is monitored by the ECM, which in turn adjusts the injector pulse width to maintain the correct fuel delivery relative to the air flow ratio. This system removes the need for a fuel pressure regulator and fuel return line on the fuel rail. The device which normally functions as a fuel pressure regulator on other ’K’ series applications is now used as an accumulator to damp fuel pump pulses in the fuel rail.
• A separate diagnostic socket, located behind the centre console in the passenger footwell, allows engine diagnostics and tuning to be carried out using TestBook, without disconnecting the ECM harness multiplug.
• The ECM controls the operation of the radiator cooling and air conditioning (if fitted) fans based on signals received from the engine coolant temperature sensor and air conditioning system. If a high engine temperature is detected, the ECM will prevent the air conditioning system from operating.
• If certain system inputs fail, the ECM implements a back-up facility to enable the system to continue functioning, although at a reduced level of performance.