Maintenance manual for sunray hfc4da1-2c china-IV diesel engines
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5) Troubleshooting
Use Sunray special diagnosis instrument to check the
trouble code and determine the malfunction position.
Mainly check the circuit of sensor and determine whether
there is short-circuit or open-circuit between circuit and the
grounding wire, whether there is short-circuit or
open-circuit to power supply, and whether the circuit is
consistent with the given pin definition.
II. Engine control unit (ECU)
1) Overview
The engine control unit is located on the firewall on the
back of the bottom of the glove box.
2) Working Principle
The ECU has one metal housing and the sensors, actuators, and power supply are connected to the ECU via multi-pole
plug. The power supply parts for direct control of actuators are integrated in the ECU so that their heat can be
effectively expanded to the ECU housing.
Requirements for ECU are as below:
- Surrounding (ambient) temperature: -40ºC~+85ºC
- Resistance to fuel, lubricating oil, etc.
- Resistance to moisture.
- The mechanical load has high requirements of the exposure to electromagnetic compatible (EMC) signal.
The ECU is used to calculate the signal received from the external sensors and control at the allowable voltage level.
Based on these input data and stored characteristic graph, the microprocessor can calculate out the duration and
accurate moment for fuel injection and convert into time-signal curve. The specific accuracy requirement and high
dynamic response of engine require high level calculation capability.
The driver stage is actuated by means of the output signal and supplies proper power to the actuators to control the
common rail pressure and the high pressure pump units. In addition, the actuators can control the engine functions
(such as relays for exhaust gas recirculation actuator, turbocharger pressure actuator, and electronically controlled fuel
pump) and other auxiliary functions (such as fan relay, auxiliary heater relay, and electric heating plug relay, and air
conditioner). The driver stage has the short-circuit protection and the protection against damage due to current
overload. These types of malfunctions and the open-circuit will be reported to the microprocessor. The diagnosis
function of the fuel injector driver stage can identify the error signal curve occurred. In addition, one series of output
signal can be transmitted to other vehicle systems via different interfaces. Within the specific safety concept
framework, the ECU can monitor the entire injection system.
The actuation of fuel injector advances special requirements over the driver stage. Within the fuel injector, the current
from the driver stage generates one magnetic field force in the magnetic coil that applies onto the hydraulic high
pressure system. To ensure the accurate tolerance and high repeatability of the fuel injection amount, this coil must be
actuated in front of a steep current wave. This requires ECU to form high voltage.
The actuation time (fuel injection duration) can be classified by the current control circuit into start current stage and
holding stage. It must work accurately to ensure that the fuel injectors can guarantee the repeatability of fuel injection
under all working conditions. In addition, it must reduce the energy loss in the ECU and the fuel injectors.
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