Engine Management System - Up to 99MY

Description
The V8 engine for models prior to 99MY is controlled by a Sagem GEMS engine management system. The ECM uses sensors to determine ambient conditions and operating data and uses this data and the information stored in an internal memory map to control the electronic ignition and fuel injection. The system features idle speed control, fault monitoring, security immobilisation and engine load management functions. GEMS can be interrogated via the diagnostic socket to access fault codes and other diagnostic information using Testbook.

The engine management system (EMS) maintains optimum engine performance over the entire operating range. The correct amount of fuel is metered into each cylinder inlet tract and the ignition timing is adjusted at each spark plug.

The system is controlled by the engine control module (ECM) which receives data from sensors located on and around the engine. From this information it provides the correct fuel requirements and ignition timing at all engine loads and speeds.

The fuel injection system uses a hot wire mass air flow (MAF) sensor to calculate the quantity of air flowing into the engine.

The ignition system does not use a distributor. It is a direct ignition system (DIS), using four double ended coils. The circuit to each coil is completed by switching inside the ECM.

The on-board diagnostic system detects any faults which may occur within the EMS. Fault diagnosis includes failure of any EMS sensors and actuators, emissions related items, fuel supply and exhaust systems.

The system incorporates certain default strategies to enable the vehicle to be driven in case of sensor failure. This may mean that a fault is not detected by the driver. The fault is indicated by illumination of the malfunction indicator light (MIL) on North American specification vehicles.

A further feature of the system is 'robust immobilisation', fitted to European specification vehicles. Upon arming the alarm, the EMS ECM disables the injectors and the Body electrical Control Module (BeCM) inhibits the crank relay (the vehicle cannot be started until the alarm is disarmed).


CAUTION: System sensor connectors can be contaminated by oil or coolant when disconnected during repair or testing. Use a suitable cap to prevent dirt or fluid ingress.