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.

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

The main features are as follows:

• The ECM controls the fuel injection quantity and timing of the fuel delivered to the 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.
• 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 connector 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.
• On engines with an intercooler (Bosch ECM), the engine management system is ’Drive by Wire’. The throttle pedal is not physically connected to the fuel injection pump, but instead connected by a linkage to a remotely mounted throttle position (TP) sensor 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 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.

Fuel injection timing

The engine control module determines the optimum fuel injection timing for the injection pump based on the signals it receives from the following sensors:

1. Crankshaft sensor - Engine speed and crankshaft position
2. Needle lift sensor - Start of injection
3. Coolant temperature sensor - Engine temperature
4. Manifold absolute pressure - Engine load*
5. Intake air temperature sensor*

*Models with intercooler (Bosch ECM) fitted