Car Isuzu Elf. Diagnosis and repair of a malfunction of the high pressure fuel pump
ISUZU ELF 4HL1
Car ISUZU ELF 2003 release of the domestic Japanese market, equipped with an engine 4HL1 with battery system Common rail. The reason for turning to the services of a car service was the inability to start the engine, and in the best traditions of the genre, the car arrived at the service on a tow truck. From a conversation with the owner, it turned out that the motor stopped at the moment of movement, which was preceded by a significant loss of power. Further attempts to start the engine were unsuccessful. The capabilities of my diagnostic equipment were only enough to read system errors. This did not clarify the situation at all, since they all had the status of saved. Identification of the causes of the malfunction remained possible only thanks to measurements directly on the power unit.
The 4HL1 engine is equipped with a DENSO battery injection system. The HP3 high-pressure fuel pump combines a booster pump and two high-pressure discharge sections.
The gear-type fuel pump with internal gearing is located in the rear of the pump with direct drive from the drive shaft. Fuel is supplied to the pump through a mesh microfilter. The pressure of the low-pressure pump enters the cavity to lubricate the eccentric mechanism and into the discharge chambers.
The fuel pump performance is limited by a pressure reducing valve. High pressure is created by two opposed plungers driven by an eccentric mechanism. Each of the discharge sections has its own inlet and discharge valves. The performance of the injection pump is determined by the SCV valve (Suction control valve), which regulates the amount of fuel entering the discharge chambers. SCV – executive component of the injection system, thanks to which the static pressure in the fuel accumulator is maintained.
The logic of the valve is such that a de-energized valve ensures maximum pump performance. The fuel rail is made in the form of a thick-walled cylindrical pipe. The prevention of pressure fluctuations that occur in the battery when the nozzles are unlocked are carried out by individual dampers (Flow damper) of each of the four injectors.
To exclude the possibility of excess pressure in the rail above the permissible limits, its internal cavity is connected to the return line through a limiting valve (Pressure limiter), which “unlocks” at pressures above 200 MPa and stops fuel draining when the pressure drops to 50 MPa.
Rail pressure is controlled by a sensor (Pressure sensor) The sensor signal is analog, has a linear relationship directly proportional to the fuel pressure.
The operation of the nozzle can be described as follows. For high pressure switching, the dimensions and power consumption of the electrovalve will exceed all conceivable sizes. Therefore, in serial nozzles, the valve does not directly control the locking needle. For this purpose, a special movable piston (Command Piston), the end of which is supported by a spring-loaded locking needle, serves. The pressure of the hydraulic control chamber acts on the piston, which communicates with the fuel supply fitting through a calibrated nozzle and with the fuel return line through an electrically controlled valve. In the case of a locked solenoid valve, the pressure in the chamber is equal to the pressure in the fuel rail, and the hydraulic piston will exert pressure on the locking needle. After the valve opens, the pressure of the hydraulic control chamber is released into the return line, and the piston relieves the force from the locking needle. The fuel pressure overcomes the force of the spring, raises the locking needle and the nozzle unlocks. After closing the electric valve, the pressure in the hydraulic chamber equalizes and the nozzle closes. The system implements sequential two-stage injection.
We are well aware that the condition for applying pulses to the control of injectors is to create a certain pressure in the fuel rail. The use of a fuel pressure sensor with an analog signal in the control system allows the measurement of the current pressure without the use of special equipment. To do this, just connect a voltmeter with large internal resistance or an oscilloscope to the signal output of the sensor. The reference voltage of the sensor, as well as a value of 0 MPa is equal to one volt. In our case, it turned out that there is no pressure in the rail. The logic of searching for the reasons for the lack of pressure is divided into two branches: these are malfunctions of the discharge section and fuel leakage in the high pressure circuits.
In our particular case, we have three combined into one drain line, This is a return flow of nozzles, a battery limiter, and a low pressure regulator in the high pressure fuel pump. Theoretically, we can assume a faulty nozzle pouring directly into the cylinder, but with so many attempts to start, including towing a car, the fuel would find itself in the exhaust system or lead to a piston water hammer. Therefore, this option is not considered. We release all fuel return lines. Then the engine rotates with a starter.
As a result of these manipulations, the presence of fuel was found out only in the return from the high pressure pump, which indicates a serviceable fuel priming pump and the integrity of the supply lines and the absence of leaks in the high pressure circuit. Thus, the fault is localized in the high pressure pump. To confirm the diagnosis, we unscrew the fuel supply pipe to the rail and make sure that there is no fuel supply. It remains to dismantle the high pressure pump and find out the cause of the breakdown. The removed pump even without opening spoke of its breakdown, the drive gear rotated without resistance. The specific cause of the malfunction was found out after dismantling the discharge sections. On the upper section of the pump, the plunger return spring broke, respectively, he remained in the upper position and did not participate in the pump. From the once whole spring, several fragments remained, some of which simply fell into the lower discharge section and jammed the second plunger.
Thus, the pump has finally failed. The successive destruction of the pump can explain the significant loss of engine power before its final stop. Damage did not affect the vital parts of the pump, and its resuscitation was reduced only to replacing a faulty spring. A suitable spring was taken from the DENSO fuel pump of the 3S-FSE engine. On each side, which had to be removed by a turn and the plane of the end face of the spring was restored by an angle grinder. The spring is slightly different in length.
After assembly of the pump it was desirable to verify its operability. In case there is no special desire to train installation skills.
To do this, with the tube connected, the discharge sections (otherwise it is impossible to determine the work of each individual), connect the fuel supply and rotate the pump drive gear with a drill.
The pump can now be seen with the naked eye and can be safely installed on the engine.
Successful launch and test drive showed the feasibility of the manipulations.
Dismantling and disassembling the high pressure pump does not cause any special difficulties. It should be noted that the pump is adjusted relative to the position of the crankshaft, for which alignment marks are applied on the pump housing.
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