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 during the compression cycle heats the injected fuel causing it to self ignite. During cold starting, automatically controlled glow plugs assist in raising the temperature of the compressed air to ignition point.

Engine Control Module (ECM)

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

The main features are as follows:

• The ECM controls the fuel injection quantity and timing of the fuel delivered to a cylinder based on inputs from sensors located around the engine. 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. The throttle pedal is not physically connected to the fuel injection pump, but instead connected by a cable to a throttle potentiometer which 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 throttle potentiometer the ECM uses the speed/density method of air flow measurement to calculate fuel delivery. This method measures the 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 determine the correct amount of fuel to be injected.
• If certain system inputs fail, the ECM will implement a back-up facility to enable the system to continue functioning, although at a reduced level of performance.
• A separate diagnostic connector, located forward of the centre console on the RH side, allows engine tuning or fault diagnosis to be carried out using TestBook without disconnecting the ECM harness multiplug.
• The ECM harness multiplug incorporates specially plated pins to minimise oxidation and give improved reliability.

The ECU inputs and outputs are shown in the following table: