Automobile actuator electronic fuel pump signal auto repair oscilloscope measurement

The function of the automobile actuator fuel pump is to suck the fuel from the fuel tank, pressurize it and deliver it to the fuel supply pipe, and cooperate with the fuel pressure regulator to establish a certain fuel pressure. The electric fuel pump continuously supplies sufficient fuel to the fuel system and maintains sufficient pressure (the pressure of the fuel system is controlled by the ECU) to ensure that the engine can effectively spray under all working conditions.

Most cars on the market currently use roller fuel pumps. Gasoline enters the pump body and is compressed by the rotor, forcing the fuel to pass through the gasoline pump at high pressure. This pump can generate a pressure of 8 bar (1 bar = 100,000 Pa) and deliver 4-5L of gasoline per minute. There is a pressure relief valve in the pump body. If the filter or other parts of the pipeline are blocked, the valve body will leave the valve seat to release the pressure when the pressure reaches 8 bar.

There is a check valve at the other output end of the gasoline pump. When the voltage of the gasoline pump is cut off, the gasoline circuit will be closed to maintain the oil pressure in the pipeline. The normal working pressure of the system is about 2 bar, and the current of the gasoline pump is 3-5A. Sparks and arcs will appear when gasoline passes through the gasoline pump rotor, but because there is no oxygen, there is no need to worry about explosion.

Let's see how to measure its current and voltage using an oscilloscope.

Connect a BNC to banana cable to channel 1 of the oscilloscope, connect the red banana plug to a needle, and the black banana plug to a needle or an alligator clip for grounding. Set the channel attenuation ratio of channel 1 to 1X, the vertical range to 5V/div or 10V/div, and the time base to about 20us.

The oil pump controller has a total of 5 wires. Line 1 and Line 2 are the power supply lines for the oil pump and are output lines. Line 3 comes from the engine main relay, Line 4 is the grounding line, and Lines 3 and 4 are input lines. Line 5 is to the engine computer, which controls the speed and power of the oil pump by transmitting a duty cycle signal. Line 1 is the same as Line 5, and the output is also a duty cycle signal, not DC power.

Insert the red probe into the No. 5 line of the fuel pump controller, and connect the black probe or alligator clip to the ground. Then start the engine.

It can be seen that it is a PWM pulse width modulation signal. The change of oil pump speed will affect the change of the signal duty cycle. The duty cycle is divided into positive duty cycle and negative duty cycle. The so-called positive duty cycle is the ratio of the positive pulse width to the entire cycle time. The negative duty cycle is the ratio of the negative pulse width to the entire cycle time. The larger the positive duty cycle, the greater the oil pressure.

We connect a current probe to channel 2, and use the current clamp of the oscilloscope to detect the current signal of the gasoline pump. The current of the gasoline pump depends on the gasoline pressure and is generally not higher than 8A. Therefore, we can select the current of channel 2 probe and adjust its vertical gear to 1A/div. As shown in the figure below, the current signal of the gasoline pump is a sine wave signal. The frequency of the oil pressure rising signal will also become faster.