If The Fuel Pressure Of The Common Rail Pipe Is Too Low, Start With These Two Conditions

Case Analysis Of Guosan Dongfeng Tianjin Fault Code 0559 Of Rail Pipe

Fault Phenomenon:

An 8-ton Guosan Dongfeng Tianjin ISDE electronically controlled common rail engine is difficult to start when it is cold, and the instrument displays fault code 0559. It can start without flameout after the oil circuit exhausts air, but it is difficult to start after 10 minutes of flameout of rail pipe.

Inspection of circuit fault and sensor fault:

The C80 is connected to the 16 pin round head diagnostic connector of ECM and displays the current fault code 0559. The common rail pressure sensor detects that “the fuel pressure in the common rail pipe is too low”, the rail pressure cannot be established and the engine is difficult to start.

Maintenance Steps:

1. Turn off the key switch, pull out the plug of the common rail pressure sensor, turn on the key switch, and use a multimeter to measure the voltage between the power pin and the loop pin in the plug of the rail pressure sensor, which is 4.99v, and the measured value meets the requirements.

2. Remove the engine ECM harness plug and measure the continuity between any two points of the power contact, circuit contact and signal contact of the rail pressure sensor; Basically, the problems in the circuit of the common rail pressure sensor are eliminated. Next, check the low-pressure oil circuit of rail pipe.

3. Check the straight pipes of the fuel tank and the connecting pipes of the low-pressure oil circuit, and replace the oil-water separator and diesel secondary filter. It is still difficult to start after the low-pressure oil circuit is vented. It is suspected that it is a problem with the fuel metering unit of the high-pressure pump. Pull out the plug of the metering unit on the high-pressure oil pump and measure the resistance of its two contacts to 3.1 Ω, which also meets the range of 2.0-4.5 Ω.

Depth Analysis

The common rail diesel engine is very sensitive to the air in the oil circuit. If there is air in the oil circuit, it will lead to the arrival of some or no diesel in the engine oil circuit. At the same time, it will also trigger the fault code of rail pressure closed-loop control mode, resulting in difficulty or failure to start the engine. The general method of air exhaust in the oil circuit is: loosen the vent bolt on the diesel filter, press the oil pump by hand until there are no bubbles in the diesel flowing from the vent bolt, and then tighten the vent bolt of rail pipe.
Rail pressure cannot be established:
If there is no air in the oil circuit, the engine still cannot be started, which involves the fault of the oil circuit. At this time, it is necessary to check in combination with the diagnostic software of the electronically controlled common rail diesel engine to check the establishment of the actual rail pressure in the common rail pipe when the starter is used to drive the engine. If the actual rail pressure value is smaller than the set rail pressure value and lasts for a long time, it indicates that the rail pressure cannot be established and the engine cannot be started. The reason is that the fuel injector used by the common rail diesel engine is electronically controlled, and a necessary condition for its fuel injection is that the pressure value of the common rail pressure sensor must be greater than or equal to a fixed value (generally 2ompa), The ECU sends the fuel injection command to the fuel injector to inject fuel, so as to ensure the smooth start of the engine.
There are two reasons why the rail pressure cannot be established:
1. The first situation is that the diesel oil in front of the common rail pipe is not enough, and it is impossible to reach the set rail pressure.
Troubleshooting: first check whether there is diesel in the oil tank. If it is confirmed that there is diesel, loosen the oil inlet pipe of the oil transfer pump, and then pump the hand oil pump. If diesel flows out from the oil inlet pipe of the oil transfer pump, it proves that there is no problem in the oil circuit from the oil tank to the oil transfer pump. If diesel cannot flow out or the amount is very small, it proves that there is a problem in the oil circuit from the oil tank to the oil transfer pump, Then check the corresponding oil circuit.
Then loosen the oil outlet of the fine filter and use the starter to turn the engine. If diesel oil flows out of the oil outlet of the fine filter, it proves that there is no problem in the oil circuit from the oil transfer pump to the fine filter. If there is no diesel flow or the amount is small, it proves that there is a problem in the oil circuit from the oil transfer pump to the fine filter, which is generally caused by the failure of the oil transfer pump.
Loosen the oil inlet pipe from the high-pressure pump to the common rail pipe (be careful not to loosen all), and use the starter to crank the engine. If diesel oil flows out of the oil inlet pipe, it proves that the oil supply of the high-pressure pump is normal. If there is no diesel oil flowing out or too little diesel oil flowing out, it may be caused by the poor oil supply capacity of the high-pressure pump or the large oil return caused by the stuck overflow valve of the high-pressure oil pump, Please check accordingly.
2. In the second case, the actual pressure in the common rail pipe has reached the set rail pressure, but due to the leakage of the oil circuit behind the common rail pipe, the actual pressure of the common rail pipe cannot reach the set rail pressure. This situation is generally due to the loose seal between the high-pressure connecting pipe and the injector, and the fuel inlet of the injector directly returns to the fuel return pipe of the injector without passing through the injector, so that the actual rail pressure cannot reach the set rail pressure.

Troubleshooting:

First, remove the fuel injector oil return pipe (behind the cylinder head), close the oil return pipe of the diesel oil circuit, open the oil inlet pipe of the oil circuit, use the starter to turn the engine, and observe the fuel return of the fuel injector. If the diesel drips out in drops, it indicates that there is no leakage; If the diesel oil is flowing, it means that the seal between the high-pressure connecting pipe and the fuel injector is not tight. Please remove the high-pressure connecting pipe of each cylinder and check its head. If the indentation is very uniform, it means that the seal is tight. If the indentation is uneven, it means that the leakage position is here.
Pay attention to check the height of the fuel injector, the head of the high-pressure connecting pipe and whether the fastening bolts of the high-pressure connecting pipe are loose. Pull out the rubber hose of the pressure relief valve on the common rail pipe, drag the engine, the oil does not flow out, and the pressure relief valve is normal. Loosen the oil inlet high-pressure steel pipe of the common rail pipe and drag the engine. The oil volume is very small and the pressure is very low.
Pull out the fuel return pipe of the fuel injector and check the fuel return volume. It is found that there are a lot of fuel return and bubbles. It may be that the fuel injector leakage causes the low rail pressure, which makes it impossible to establish the rail pressure in the common rail pipe. After removing the fuel injection nozzle for inspection, it was found that the bolts of the fixed seat of the fuel injection nozzle of the first cylinder and the fifth cylinder were loose. Finally, the problem was found out and the bolts of the fuel injection nozzle seat were tightened.

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