Fuel Pump Assembly: Components (Working Principle) And Problems



When we talk about the fuel system, the first thing that comes to mind is the fuel pump. It is impossible to supply fuel to the engine without this thing. Due to the heat dissipation, sound insulation and air resistance, the fuel pump is located in the fuel tank. Its primary function is to suck out the fuel from the tank, pressurize it and deliver it to the fuel pipe.


The fuel pump assembly plays an essential role in the fuel pump system. It is an integrated part containing several components, mainly a filter (fuel filter, suction filter), fuel pressure regulator, fuel pump, and fuel gauge sensing unit (with fuel float).


1. Components

    1.1 Filters

    1.2 Fuel pump

    1.3 Fuel pressure regulator

    1.4 Fuel gauge sensing unit

2. Troubleshooting

    2.1 Method 1: Electrical test

    2.2 Method 2: Fuel pressure test

    2.3 Fuel gauge sensing unit issues

3. Tips and warning


1. Components


Let's take a look at components in the fuel pump assembly.


1.1 Filters


The filters can be divided into the suction filter and fuel filter. Commonly known as the coarse filter and fine filter, they are mainly used to filter the impurities in the fuel. The fuel filter is more important. The structure of the fuel filter consists of an aluminium shell and a bracket with stainless steel inside.


1.2 Fuel pump


The fuel pump is the core component of the fuel pump assembly. It is to suck fuel out of the fuel tank and deliver it to the fuel pipe.


Trustworthy Fuel Pumps


When the fuel pump works and how long it works is controlled by the ECU according to the vehicle's actual situation. The fuel pump is powered directly from the car battery. The fuel pump relay controls its on/off. The circuit issues are caused mainly by a faulty fuel pump relay.


The fuel pump motor is energized to drive the inner rotor to work. The volume increases at the inlet chamber to form a vacuum to suck fuel.


Under the centrifugal force, the inner rotor presses against the outer rotor and drives the fuel from the inlet chamber to the outlet chamber through a narrow gap. The volume decreases at the outlet, forming high pressure. The fuel is pumped from the outlet.


1.3 Fuel pressure regulator


The pressure regulator has the role of fuel pressure regulation and pressure stabilization to control the fuel pressure at about 0.4 MPa (depending on the engine model, the specific pressure value may also vary).


Trustworthy Fuel Pressure Regulators


The pressure regulation is that when the fuel pressure exceeds the spring pressure of the regulator, the valve opens and allows the fuel to flow back to the fuel tank. Thus the fuel pressure is constant.


1.4 Fuel gauge sensing unit


What are we talking about here is the variable resistance fuel level sensor, consisting of a fuel float, a variable resistor, and a metal rod connecting the two parts.


The fuel float can move up and down with the fuel level change. The sliding arm slides on the resistance, thus changing the resistance value between the hitch and the fuel float. It uses the resistance value change to control the circuit and displays the value on the meter.


2. Troubleshooting


Is your car hard to accelerate (especially when driving on the highway)? Is the car showing signs of low fuel? The fuel pipe, filter, pump or injectors are likely clogged or partially blocked.


If you can't start your car at all, you may want to check the fuel pump quickly. When it doesn't work, check the fuel pump circuit first. Then check the fuel pipe pressure.


2.1 Method 1: Electrical test


Measure the fuel pump power supply terminal. The voltage should be the battery voltage. If the voltage is abnormal, it may be issues of fuel pump relay or fuel pump wiring harness.


●  Check fuel pump fuse


Usually, it is not the fuel pump that fails but the electrical supply. Check the manual to find the location of the fuse box. Next, find the fuse that corresponds to the fuel pump. Remove the fuse and check for signs of failure. The fuse may be melted or blown.




If the fuses look OK, check the other fuse sections associated with the fuel system for signs of wear and replace them if necessary.


If you need to replace a fuse, make sure you use a fuse with the proper current rating. Do not install a fuse that is rated for too much current.


A blown fuse may mean that the circuit is drawing too much current. You need to check the individual circuits. Get someone to help you start the car or take it to a repair store to check the relay.


●  Check fuel pump voltage


The current flowing through the circuit does not necessarily go to the fuel pump, so you must also check the voltage. Look through your car's manual to see which parts you need to check and the correct procedure to do so.


Test the voltage source to verify that the current is flowing to the fuel pump after it leaves the fuse.


●  Voltage drop test with voltmeter.


Make sure the wires have adequate voltage and that the ground wire is properly grounded. If the electrical test shows that everything is fine, it is likely that the fuel pump is faulty and needs to be replaced. You can perform a separate oil pressure test to do a more thorough check.


If the voltage difference is more than 1 V, the wire may be corroded, or there may be a problem with the positive or negative terminal of the circuit. Take it to a repair store for more in-depth testing and get further advice.


2.2 Method 2: Fuel pressure test


Fuel pressure is measured by a fuel pressure gauge, which should be around 0.4 MPa (depending on the engine model, the specific pressure value may vary). If the pressure is abnormal, the fuel pressure regulator, fuel pump, or filter may have problems.


●  Exclude the possibility of filter failure


A clogged filter with carbon deposits can also make it hard to accelerate the car (while you suspect the problem is with the fuel pump). Check the short fuel feed hose and blow air into it to make sure there is not much resistance. Check the filter for debris and replace it if necessary.




●  Purchase fuel pressure gauge


Most auto parts stores have fuel pressure gauges. This is a good investment and is used for most models. If you don't want to buy one, you can also borrow one from a that allows customers to borrow tools. The fuel pressure test only takes a few minutes to complete.


●  Connect the pressure gauge to the fuel pump unit


Find the location of the fuel pump (usually near the carburettor or injector). Then find where the fuel pump connects to the filter housing. There should be a small connector there for the pressure gauge.


Each type of pressure gauge may be used slightly differently, and the location of the fuel pump is different for each model of car. So look in your car's manual for more detailed information.


●  Get someone to help you start the engine when checking the pressure gauge


Let the engine warm up a little. Check the fuel pressure when the car is running at idle and at the rated RPM (check fuel pump specs). 


If you don't know the rated RPM, start the engine and see what difference the fuel pressure makes. If the problem is severe and the needle on the pressure gauge doesn't move, you need to replace the fuel pump.




The fuel pressure must meet the specifications listed in the owner's manual and should increase when the engine runs at a certain point.


If the pressure does not increase or the difference between the inlet and outlet pressures is more than 28 kPa (4 psi), you need to replace the fuel pump.


2.3 Fuel gauge sensing unit issues


When the fuel level does not match the actual level, you can determine whether the fuel level sensor is normal by measuring the resistance value of the fuel level sensor.


Place the fuel float in E (empty), LOW (low fuel level) and F (full) respectively to measure the resistance value of the fuel level sensor and compare it with the standard value for any abnormality. If there is any abnormality, the fuel float may be malfunctioning.


3. Tips and warning


Need a fuel pump replacement? Actually, a refurbished fuel pump is just as good as a new one. It is cheaper. Some manufacturers have kits available for refurbished fuel pumps if you're adventurous.




You can follow the instructions in the kit to disassemble the fuel pump with a screwdriver and rebuild it. If you don't like this idea, you can ask the service center to find and refurbish the fuel pump for you. It should have at least a 3-month warranty.


Remember to turn off the engine before fuel spills. Be careful not to spill fuel. Spilled gasoline can easily cause the vehicle fire.

Updated Products

Delcoribo Motor Products Co., Ltd.

Economic Development Zone, Jinhua, Zhejiang, China

Tel: +86-579-8275-8180

[email protected]

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