Electronic diesel control operation (Engine management system - EDC)

ELECTRONIC DIESEL CONTROL OPERATION

Diesel engines operate by compression ignition. The rapid compression of air in the cylinder is heated during the compression cycle. The fuel is injected into the compressed, heated air and spontaneously ignites. Automatically controlled glow plugs are used during cold starting to reduce post start emissions and assist cold starting by raising the temperature of the compressed air to ignition point.

Electronic Control Module (ECM)

The Electronic Control Module (ECM) processes all inputs and outputs related to the operation of the electronic diesel control. The ECM is located on a mounting plate behind the battery in the engine compartment. The ECM comprises an aluminium cast body with a galvanised sealed lid. A socket is positioned on its upper face and receives a multiplug from the engine wiring loom. The socket contains 55 pins although only the pins corresponding to those in the multiplug are used.

The multiplug is connected into the engine compartment wiring loom. All inputs and outputs to and from each sensor is transmitted through the loom and via the multiplug, to the ECM. The multiplug fits into a corresponding socket on the upper face of the ECM and is locked in position with a cam type locking lever. The multiplug pins are plated 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 inputs, the ECM can adjust the quantity and timing of the fuel being delivered to the cylinder.

Main Features

The main features are as follows:

• The ECM incorporates short circuit protection and can store intermittent faults on certain inputs. TestBook can interrogate the ECM for these stored faults.
• The engine management system is a ’Drive by Wire’ system, with no mechanical link between the throttle pedal and the fuel injection pump. All throttle movements are monitored by the ECM via a throttle position (TP) sensor which is located on the pedal box. The sensor provides the ECM with a signal proportional to throttle pedal movement. The ECM then adjusts the fuel injection pump to deliver the required amount of fuel.
• In conjunction with the TP sensor, the ECM uses engine speed, calculated from the Crankshaft Position (CKP) sensor, to determine the basic fuelling requirements of the engine. This basic calculation is modified using signals from sensors, strategically positioned around the engine, to ensure that the correct fuel mixture is achieved for optimum performance and emissions.
• 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.
• A separate diagnostic socket, located behind the centre console in the passenger footwell, allows engine tuning or fault diagnosis to be carried out using TestBook.
• The ECM also operates the engine immobilisation circuits. When the ignition is switched to position II, a coded signal is sent to the ECM from the Central Control Unit (CCU). If the coded signal does not match the signal programmed into the ECM, the ECM immobilises the engine starting circuits.
• On vehicles fitted with ABS, the ECM provides signal information to the ABS ECU for hill descent control.