Doosan D20S-5 Operation & Maintenance Manual page 127

Operation Section
Electronic Controlled Spark-Ignition Engines
G430FE Engine
The primary components of the fuel system are the fuel supply, direct electronic pressure regulator (DEPR),
fuel mixer, electronic throttle control (ETC) device, 2-Stage convertor, engine control module (ECM), and a
catalytic converter. The system operates on a slightly positive fuel pressure. Primary fuel pressure can be
measured at the LD 2-Stage convertor. Secondary fuel pressure command and actual fuel pressure is
monitored by the ECM.
To obtain maximum effect from the catalyst and accurate control of the air fuel ratio, the emission certified
engine is equipped with an onboard computer or Engine Control Module (ECM). The ECM is a 32 bit
controller which receives input data from sensors mounted to the engine and fuel system and then outputs
various signals to con¬trol engine operation.
One specific function of the controller is to maintain a closed loop fuel control which is accomplished by use of
the Heated Exhaust Gas Oxygen sensor (HEGO) mounted in the exhaust system. The HEGO sensor sends a
voltage signal to the controller which then outputs signals to the EPR to change the amount of fuel being
delivered from the regulator or mixer to the engine.
The controller also performs diagnostic functions on the fuel system and notifies the operator of engine
malfunctions by turning on a Malfunction Indicator Light (MIL) mounted in the dash. Malfunctions in the
system are identified by a Diagnostic Trouble Code (DTC) number. In addition to notifying the operator of the
malfunction in the system, the controller also stores the information about the malfunction in its memory. A
technician can than utilize a computerized diagnostic scan tool to retrieve the stored diagnostic code and by
using the diagnostic charts in this manual to determine the cause of the malfunction. In the event a technician
does not have the computerized diagnostic tool, the MIL light can be used to identify the diagnostic code to
activate the "blink" feature and count the number of blinks to determine the diagnostic code number to locate
the fault in the system.
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