The fuel pump is one of the most important components of the engine power system. A pump malfunction leads to interruptions in the operation of the internal combustion engine, failures when pressing the gas, or even problems with starting. Let's look at the design and operating principle of fuel pumps for injection and carburetor engines; Let's talk about breakdowns and diagnostic methods.
According to their operating principle, fuel pumps (FP) of gasoline internal combustion engines are divided into 2 types:
- electrical;
- mechanical.
During engine operation, the fuel pump is used to pump fuel from the tank to the carburetor or fuel rail with injectors. On cars with direct injection and a high-pressure fuel pump (HPF), the fuel pump is used as a booster section.
Types of fuel pumps
Current models are equipped with both mechanical and electrical fuel pumps. Mechanical pump
found in carburetor cars,
electric fuel
injection pump, where fuel enters the car engine under pressure.
The mechanical gasoline pump is located outside the gas tank, but the electric one, on the contrary, is located inside it. There are cars in everyday use that have 2 fuel pumps installed. The mechanical unit operates under low-frequency pressure because the carburetor and fuel pump are located close to each other.
Gasoline pump, device and principle of operation, where the gas pump is located
Mechanical pumps are installed only on the fuel line, outside the tank. Some types of car engines are equipped with two fuel pumps at once - one operates at high engine loads, pumping large volumes of fuel under low pressure, and the other, located inside the tank, supplies fuel in small volumes under high pressure.
A mechanical pump sucks fuel from the tank and delivers it to the carburetor through the fuel filter. The electric pump “pushes” fuel from the tank into the injectors under high pressure.
On cars equipped with a carburetor fuel supply system, the fuel pump operates constantly and at the same speed, and in more modern injection systems, the unit supplies fuel at the speed set by the electronic control unit.
fuel pump connection diagram
The mechanical fuel pump is mounted very simply - in the provided mounting location. After installation, all that remains is to connect the fuel supply line hose to the inlet and outlet ports, after which the unit is completely ready for operation.
As for electric pumps, two connection schemes are practiced on modern cars: Long fuel supply ring - return of unused fuel from the injectors back to the tank. Short ring – return of unused fuel to the tank directly from the fuel pump.
mechanical fuel pump
The device of this unit is quite simple:
• Lid. • Strainer. • Upper part of the body. • Top plate. • Working diaphragms. • Bottom plate. • Rod. • Return spring. • Lower part of the body. • Manual fuel pumping lever.
The entire structure forms a chamber equipped with inlet and outlet valves, which are located in the upper part of the pump housing. Valves are simple textolite washers that press springs to valve seats.
The operating principle of the pump is as follows: the drive lever of the unit moves up and down constantly, but the diaphragm moves only at the moment when it is necessary to fill the pump chamber with fuel. The diaphragm returns to its original position under the action of a return spring. Actually, this is how fuel is supplied to the carburetor.
If we consider the functioning of a mechanical fuel pump in more detail, we find some differences in operation on the engines of rear- and front-wheel drive cars. If the car has rear-wheel drive, then an eccentric is installed on the drive shaft, which pushes the fuel pump rod, thereby ensuring its operation.
Front-wheel drive engines also have an eccentric inside, but it is mounted on the camshaft. During operation, the pusher presses on the lever, which, in turn, acts on the balancer in the lower part of the fuel pump housing. The balancer pushes the spring resistance and pulls down the rod with the pump diaphragms - a vacuum is obtained. Fuel is drawn through the fitting, the inlet valve opens and passes it into the cavity above the diaphragm. After this, the return spring pushes the rod with the diaphragm upward - pressure is created in the working chamber of the pump. Under the influence of pressure, the inlet valve closes and the outlet valve opens. Fuel enters the outlet fitting, follows the hose and enters the carburetor.
electric fuel pump
Structurally, in a number of some parts, the unit is similar to a mechanical pump. The operating principle of an electric fuel pump is as follows: a special core is drawn into the solenoid valve, creating pressure until the voltage supply contacts open. When the key is turned in the ignition switch, the fuel pump starts working, raising the pressure in the system to the operating level. Therefore, before starting the engine, it is strongly recommended to wait a few seconds so as not to subject the fuel pump to unnecessary load.
In some car models, the fuel pump starts when the driver's door is opened. The unit can create a working pressure of 0.3-0.4 MPa; in engines with direct fuel injection, this figure can reach 0.7 MPa.
An electric pump has a diaphragm inside it that moves up and down. When the diaphragm moves down, a vacuum is created, opening the inlet valve of the pump. Gasoline flows through the filter into the chamber above the diaphragm. As it moves upward, it creates pressure that closes the intake valve and opens the exhaust valve - the fuel moves further along the line.
The design of the electric pump is as follows:
Features of fuel pumps
Submersible fuel pump
To determine where the electric fuel pump is located in the system, it is necessary to take into account its design features. For example, rotary and gear pumps are installed directly in the fuel pipeline system, and the centrifugal pump is always located in the gas tank. Based on their location, fuel pumps are divided into:
- Remote - mounted on the car body.
- Submersible - installed in the fuel tank so that it is immersed in fuel. Such designs are most popular in modern cars. By immersing the mechanism in the working fluid, it is cooled and the possibility of “dry running” is eliminated. The submersible fuel pump module consists of a fuel level sensor, a coarse fuel filter, the electric fuel pump itself and a pressure regulator.
In cars with a gasoline engine, the fuel pump creates high pressure in the range of 0.3-0.4 MPa. Direct fuel injection systems can provide pressures of up to 0.7 MPa.
The electric pump is turned on using a relay receiving a signal from the engine control unit. Power passes through the fuse in the fuel pump circuit, causing the latter to operate simultaneously with the ignition system being turned on or immediately after opening the driver's door. The relay itself can be located near the engine control unit or as part of the fuse box.
How to check the pressure in the fuel rail?
You will need a pressure gauge that measures pressure in the range from 7 to 10 atmospheres. If you choose a pressure gauge with a large margin, you risk getting less accurate measurement results. Specialized stores sell a kit for measuring pressure, but you can also design your own device.
If you want to assemble the device yourself, you will also need a hose with an internal diameter of 9 millimeters. You will also need plumbing tow, with which you can seal the connection between the pressure gauge and the tube. All parts are connected and tightened using a clamp. You will also need a car spool. Next you need to perform a series of actions:
- Place the car on a level surface that is prevented from rolling, turn off the ignition and open the hood.
- Check that the injection nozzles have access to the fuel rail.
- Find the fuel pressure plug and remove it. Then you should unscrew the nipple using the spool.
- Prepare an empty container (a regular bucket will do) and a clean rag. This is necessary to collect residual fuel, which under pressure can splash out in different directions. Therefore, take care of the safety of your skin (especially your face and eyes).
- Connect the device to the fitting and begin checking the mechanism.
Checking the pressure in the fuel rail should occur in four operating modes of the power unit:
- when the ignition is on;
- at idle engine speed;
- code the fuel pressure regulator tube is reset;
- when the drain tube is compressed.
Filter and mesh of the electric fuel pump, why they are needed and how often they are changed
Fuel from the gas station usually needs additional cleaning. The injection system is especially sensitive to fuel quality. Fuel filters are used for additional cleaning. The cleaning process is carried out in two stages: first, rough cleaning - through the fuel pump mesh.
Large particles of rust and debris are filtered out here. The second stage is fine cleaning, which is performed by the fuel filter. In different car models, fine filters are installed in different places. Most often it can be found under the hood of a car.
The injection system requires very thorough cleaning of the fuel - from 5 micrometers. The pressure in such a system is quite high, so fuel filters are made of durable material or stainless steel.
replacing the fuel filter
The engine owner's manual should indicate how often the fuel filter needs to be changed. Most often, this procedure is carried out once every two years or after a certain mileage of the car. However, given the quality of fuel at domestic gas stations, it is recommended to change the filter at least once a year. During intensive use of the car, it is recommended to periodically check the fuel filter and, if necessary, change it immediately.
You can replace the filter at a service station or yourself - the procedure is simple. Before changing the fuel filter, it is necessary to relieve the pressure in the rail.
For this:
• Disconnect the minus terminal. • Remove the fuel pump relay. • Connect the terminals to the battery. • Start the engine and wait until it stalls.
Now you can remove the fuel filter. We pinch the latches on both sides of the filter with our fingers and carefully remove it. Remember - approximately 100 grams of fuel remains inside the filter and it can leak out. Next, we perform the steps in reverse order - install a new filter, disconnect the terminals, replace the relay, connect the terminals, start the engine. We check for leaks at the connection between the filter and the fuel hoses.
We recommend: Checking the level and changing the oil in the Lada Granta gearbox
It is very important to be able to determine when the filter is clogged. First of all, this can be signaled by poor engine starting; traction drops significantly; during sharp acceleration, the engine “chokes” and may stall. At idle, the engine runs unevenly; while driving, the engine lacks fuel if the speed exceeds 100 km/h.
Car won't start after replacement
Car won't start after replacing fuel pump? This phenomenon is not uncommon. In many cases, this is not a problem. The car cannot start immediately because the pump takes time to pump up the pressure that was previously reduced. To bring the pressure to the optimal level, you need to turn on the ignition for 5 seconds so that the instrument panel lights up. Next, turn the engine with the starter. If it doesn't work on the first try, you should wait about a minute and try again.
If cranking the starter does not help start the engine, then one of the following reasons may be occurring:
- errors were made when assembling or connecting the BN;
- the new fuel module is faulty;
- the car's security system has gone down or a blockage has occurred;
When installing and connecting a new pump, failures of various types are possible: from malfunction of the valves on the fuel pump to breakage of contacts, terminals or connectors.
It is important to identify the exact nature of the problem and determine its type - electrical or mechanical. The simplest breakdown relates to the power supply to the fuel pump; it either exists or it doesn’t. If we are talking about an immobilizer or alarm system, then the anti-theft system can turn off the power supply to the BN, preventing the car from starting. Don't forget about filter clogging either. If the valves are stuck, the device can operate and produce characteristic sounds, but at idle.
The listed malfunctions prevent fuel from entering the ramp, so the engine cannot start. To clearly determine the cause, it is important to make sure that there is no gasoline in the rail. Next, it is recommended to dismantle and connect the BN from the dimensions or batteries directly. This method is considered the fastest for checking the device.
How does a fuel pump work?
The electric pump seems to push the supplied fuel inside the car engine. Fuel pump device
in older car models it is such that their unit operates at a fixed speed. New models are designed in such a way that the speed of the unit depends on the motor. The electric fuel pump depends directly on the electrical system of the car, which takes into account indicators such as the aero-fuel ratio, throttle position, and the amount of exhaust emissions contained.
Such units begin to work when the electric motor starts. When you turn the ignition switch, the on-board computer is activated and a signal is given to start the fuel pump. When an electric charge is applied, the motor inside such a pump begins to rotate, thereby creating pressure in the fuel system. If there is no engine signal for more than a few seconds, the fuel pump will be automatically turned off.
How does a fuel pump work?
, is heard during the first moments of starting a car engine. Next, gasoline enters the fuel pump through a tube and exits through a one-way valve, and then passes through the fuel filter into the car engine. While the engine is running, the fuel pump will also work.
The design of the car's power system and the operation of the fuel pump
Electric fuel pumps push fuel into the engine. The operation of the electric fuel pump is controlled by the vehicle's electronic system, which takes into account throttle position, air-to-fuel ratio and exhaust emissions.
Since electric fuel pumps operate under pressure, they are quite noisy and heat up quickly. It is for this reason that they are placed in the fuel tank - the fuel cools the fuel pump and muffles noise.
Signs of malfunction, their causes
- Most often, fuel pumps suffer from overheating. Even 10 minutes of operation without proper cooling can damage the pump motor.
- The second enemy is water and dirt. Condensation collects in the gas tank, which then gets into the gasoline and causes corrosion of both the tank itself and the gas pump housing.
- Mechanical impurities can also damage the pump. As a rule, it comes with a mesh fuel filter that can be washed and reused. But if grains of rust and other rough particles begin to penetrate inside the case, they will quickly damage the mechanism.
- Finally, where there is electricity, there is a problem with wiring. Electric pump wires suffer from vibration, fray and break.
The main signs of a malfunction are either complete pump failure or incorrect fuel supply, which causes the engine to run unevenly and the fuel pump does not work. If during acceleration the power suddenly disappears or the same happens when transporting cargo, the engine does not start or starts with difficulty, or runs unevenly, this may be due to the fact that the pump has failed.
Fuel pump design
Depending on the type of drive, fuel supply pumps are divided into two large groups: mechanical and electrical. The former are used only in carburetor engines, and also as booster pumps in diesel engines. The latter are used for both gasoline and diesel engines.
Mechanical fuel pumps
Mechanical fuel pump design
The mechanical pump is located on the engine and driven by a special eccentric. Structurally, it consists of the following elements:
- frame;
- diaphragm;
- pusher;
- stock;
- return spring;
- valves on the suction and discharge channels;
- filter;
- eccentric.
In cars equipped with rear-wheel drive, the eccentric is located on the oil pump drive shaft, and in cars with front-wheel drive it is located on the engine camshaft. The movement of the diaphragm in such a pump ensures the movement of fuel. When the diaphragm is at its lowest point, a vacuum occurs in the working chamber, and the latter is filled with liquid. When the diaphragm moves to the upper position, fuel is pushed into the discharge pipe. The valves prevent the fuel from flowing back.
For diesel engines, such systems are often used as low pressure pumps. They perform the function of pumping fuel and are located next to the high pressure pumps (HP pumps). On the practical side, this allows you to overcome the hydraulic resistance of the filtration system and create a stable excess pressure.
Electrically Driven Fuel Pumps
Roller fuel pump. 1 – check valve; 2 – safety valve; 3 – electrical connector; 4 – electric motor; 5 – impeller
Electric pumps are installed on engines with distributed and direct injection. They are driven electrically by a battery or generator. According to their design, electric pumps are divided into the following groups:
- Vacuum. Such a pump has a similar design to a mechanical one, but the eccentric that drives the working units is replaced with an electric drive.
- Roller. In such a device, fuel moves due to the rotation of the rotor (movement of the rollers). At the moment when the distance between the roller and the rotor increases, a vacuum occurs, the suction valve opens, and the fuel is sucked in until it is completely filled. At the next moment, the rotation of the rotor ensures that the distance decreases, and fuel is supplied to the engine through the opened injection valve.
- Geared. Suction and injection of fuel is realized through the rotation of the rotor gear. It is located eccentrically with respect to the stator gear. The teeth of the gears form chambers through which the fuel passes. During rotation, the volumes of the chambers constantly change, which ensures the required pressure.
- Centrifugal. Such a pump has an impeller equipped with blades that move fuel from the suction to the discharge channel. Pressure is created due to the turbulence that occurs when the blades act on the working fluid.
- Plunger Gasoline pumps of this design are rare. Such systems are mainly used in diesel vehicles as injection pumps. They have pairs of plungers driven by a cam shaft. As the plunger moves upward, the outlet and inlet holes are closed sequentially. This forms the pressure necessary to open the injection valve and subsequently supply fuel to the engine injectors.
Mechanical VT
This type of pump operates from the engine camshaft. Rotation of the eccentric provokes pressing of the lever (pusher). The photo shows a domestic design consisting of a lever and a balancer. Among foreign manufacturers, the more common design is with a double-arm lever (rocker arm).
The thrust of the pump with the diaphragm, when the pusher acts on the balancer, overcomes the resistance of the spring, lowers and draws in fuel through the inlet valve. As soon as the eccentric releases its pressure, the spring returns the diaphragm, pushing fuel to the carburetor through the exhaust valve. When the float chamber is filled, a pressure is created in the space above the diaphragm that the spring cannot overcome. And since the balancer and the pump rod are not connected to each other, the balancer can move idle. As soon as the pressure in the float chamber drops, the diaphragm squeezes out gasoline - the operation of the fuel pump resumes.
Is it possible to repair a fuel pump yourself?
Mechanical fuel pumps, due to their simple design, are subject to repair - in fact, there is nothing special about them that can break. Most often the membrane fails, sometimes the rod. All this can be replaced, although most car enthusiasts prefer not to bother and buy a new pump - it is inexpensive and can be replaced in literally 10 minutes.
As for the electric fuel pump, it is not recommended to repair it, especially on your own. Theoretically, the electric fuel pump cannot be repaired - this is provided by the manufacturer. In practice, some craftsmen open the case and try to repair or replace damaged or failed parts. Such amateur activity is fraught with serious damage to the fuel system, so there is no point in experimenting, and it is better to purchase a new pump.
Diagnostics, who can diagnose the operation of the fuel pump, advice from the pros
Of course, the most accurate and high-quality diagnostics of a fuel pump, especially an electric one, can only be done at a specialized service station. However, some manipulations, especially if the machine is domestically produced, can be done independently.
The first thing you should check is the fuel pump fuse. Next, the fuel pump relay needs to be checked. To do this, check the presence of voltage at the control terminals, and touch the ground with the other end. The test is carried out using a multimeter or a test lamp, with a current consumption of no more than 0.25 A. If the fuse is working and the lamp does not light, you should look for the cause in the wiring and control unit.
The electric fuel pump is checked as follows: if the fuel pump is not removed, measure the voltage on its chip. The removed fuel pump is connected to a 12V source, for example, to a car battery.
Checking a mechanical fuel pump is extremely simple: remove the hose from the outlet fitting and press the manual pump lever several times. If fuel flows, the pump is working. In the case when manual pumping works, but no fuel is supplied while the engine is running, the reason is most likely a worn-out rod. Due to constant contact with the eccentric, the pump rod may “shorten” over time and simply not reach the lever. In this case, the part needs to be replaced - the fuel pump rod costs a penny and can be replaced in 10-15 minutes.
Main fuel injection pumps of the Common Rail system
In such pumps, which work primarily with diesel engines, fuel is collected in a special ramp before being pumped into the injectors. The intermediate accumulator in the injection pump is used to generate sufficient pressure (but not excessive), as well as to compensate for losses caused by the failure of individual injectors. Depending on the required level of injection force, designers can install one, two or three plungers in such systems.
Methods for dispensing fuel into the injection pump
The cyclic supply of diesel, in contrast to injection and carburetor gasoline pumps, ensures more accurate energy consumption. Due to an additional device - a bypass valve, excess fuel is removed at excess pressure.
The classification uses three types of devices:
- With throttling at the moment of fuel intake;
- With cut-off function;
- With a combination of dosages.
Fuel volume control can be mechanical (spring) or electronic.
