Fuel System Failure Analysis

Testing The Fuel System

The function of the fuel system is to supply a certain amount of clean, well-atomized gasoline to the engine according to the engine operating conditions in order to mix with a certain amount of air to form a combustible mixture. At the same time, the fuel system also needs to store a considerable amount of gasoline to ensure that the equipment has a considerable driving range.

Failure Phenomenon Analysis

1、Testing the fuel system

The diagnosis of the fuel system can be divided into two parts: the diagnosis of the fuel supply system and the diagnosis of the oil injector nozzle circuit system. The fuel supply system can be tested by measuring the flow and pressure of fuel. The best way to measure the amount of fuel is to test it when there is a load in the fuel supply line.

2、Check the fuel pump and control circuit

If the fuel pump or control circuit is faulty, it can also cause the fuel supply system to have no fuel pressure. Even if the injector nozzle is working properly, fuel will not be injected properly.

The inspection method is: to connect the diagnostic plug terminals +B and FP with short wires, then turn on the ignition switch and check whether there is pressure in the fuel inlet hose.

If there is pressure in the hose and the sound of returning fuel can be heard, it means there is no problem with the fuel pump itself; otherwise, the fuel pump should be checked and the resistance between the two terminals of the fuel pump can be measured with a multimeter. If it does not match the regulations, the fuel pump needs to be replaced. If there is a problem with the ignition switch, it should also be replaced, and the cost of ignition switch replacement can be within an acceptable range.

If the fuel pump is working properly, then its control circuit should be checked. Check mainly the fuses, EFI main relay, fuel pump relay, resistors, and each wiring and connector.

3、Check the fuel pressure regulator

The fuel pressure of the fuel system has a direct impact on the concentration of the mixture, so the fuel pressure should be checked first.

The method is: first the fuel pressure gauge is into the fuel line, and then start the engine and measure the fuel pressure.

If the fuel pressure is too high, the pressure regulator should be replaced; when the pressure is too low, the return hose can be clamped, and if the fuel pressure rises to a normal value, the fuel pressure regulator is damaged, otherwise, the fuel pump and fuel filter can be checked.

Check the fuel pressure after turning off the engine, it should keep the specified value for 5 minutes. Otherwise, it means that the fuel injector is leaking, resulting in a too-rich mixture.

4, check the fuel pump and fuel filter

When starting difficulties, the fuel pump is generally able to work normally, and the problem is that the fuel pump filter is clogged, resulting in the fuel pump can not suck in sufficient fuel or the fuel filter is not smoothly caused by insufficient pressure in the fuel supply system.

5、Check the cold start system

In some models, there is a cold start injector to thicken the mixture during the cold start to improve cold start performance. The cold start injector is controlled by the start switch and the thermal time control switch. The duration of oil injection depends on the thermal time control switch heating coil current and the temperature of the cooling water.

6、Check the anti-theft system

The vehicle immobilizer system can also produce some often overlooked fuel supply system failures. Some equipment manufacturers include a parameter identification function in the immobilizer system data stream.

In many models, replacing the module of the immobilizer system without properly initializing it can result in the device not starting. There are also devices that require the multifunction controller to be replaced in order for the engine to start properly under certain specific circumstances, such as when the master key is lost.

Check Coolant Temperature Sensor

Coolant temperature sensor affects the amount of engine injection, making the mixture too thick or too thin, making the engine combustion situation worse, so that the engine is not easy to start, and running unstable.

Failure Phenomenon Analysis

1, resistance check: turn off the ignition switch, unplug the sensor, and use a multimeter to detect the resistance.

2, output signal voltage check

3, and ECU connection harness resistance value check: the resistance of the sensor and ECU ends should be less than 1Ω.

Check The Air Flow Meter

Now the equipment, the throttle position sensor data directly determine the amount of fuel injection other, airflow meter, intake air temperature these data are only used as a small adjustment, where the airflow meter data for the ECU to adjust the amount of fuel injection and ignition time so that the engine in a variety of operating conditions to obtain the best concentration of the gas mixture.

Failure Phenomenon Analysis

1、Resistance test: The resistance test of this project is an auxiliary test. Mainly to detect the conductivity of the wiring harness to confirm that the wiring harness is smooth, with no breaks, or short circuits. The plug connector is secure, and the signal transmission is without interference.

2, voltage test: this project voltage test has two parts: power supply voltage test and signal voltage test, of which the signal voltage test is the main basis for determining whether the airflow meter is effective.