There are factors that influence what fuel pressure should be in the fuel injection pump. It must correspond to the parameters specified by the engine manufacturer. Accordingly, depending on the type of pump, the type of power unit and the intended operating conditions, the pressure range will change.
This parameter is mainly influenced by the type of engine – gasoline or diesel. The pressure in the latter is much higher, and this must be taken into account when diagnosing. In general, this indicator should be specified in the engine documentation, but sometimes it is necessary to measure it yourself in cases of problems with the fuel system.
The essence and tasks of fuel injection pump
The high-pressure fuel pump (or injection pump for short) is the most important part of the system that supplies the diesel power unit with fuel. However, such pumps are also made for gasoline engines. The difference between the two indicated types of elements is the level of pressure created. This is due to the design features of diesel and gasoline engines.
In a diesel engine, the air that fills the combustion chamber during the “intake” stroke is compressed during the “compression” stroke. At the same time, not only its pressure increases sharply, but also its temperature, which rises above the level of self-ignition of diesel fuel.
When the piston reaches TDC (top dead center), fuel is injected into the combustion chamber through the nozzles, which instantly ignites. Accordingly, the fuel passing through the injectors must overcome enormous pressure. It is for this counteraction that the injection pump is responsible.
In addition, the pump must regulate the fuel supply, that is, supply it in certain doses and at the right time. The last function depends on the rotation of the crankshaft, but the accuracy of operation (taking into account the number of revolutions) is very important here. On modern diesel models, the timing of the fuel supply is controlled by a computer – an electronic control unit.
History of injection pump
The injection pump was invented in the 30s of the last century by engineer Robert Bosch. Initially, such fuel pumps were installed on powerful diesel engines for trucks, but already in the second half of the 1930s, passenger car engines also began to be equipped with high-pressure pumps.
Gasoline engines did not need high fuel pressure, since they were equipped with carburetors, and the fuel-air mixture was supplied to the combustion chamber under the influence of vacuum created during the “intake” stroke. However, in our time, carburetors are already a rarity – they have been replaced by direct injection systems that provide fuel injection, which again uses injectors that require high pressure.
It is interesting that the operating principle of the fuel injection pump has not changed in any way since its invention. However, individual parts and mechanisms have undergone numerous modernizations. This was required by improving environmental standards, as well as the desire of manufacturers to increase the efficiency of engines.
The first in the series was an exclusively mechanical pump model, but it cannot even be called economical even with a certain degree of approximation. Equipping diesel engines with this injection pump entailed high fuel consumption, which often did not have time to burn completely, as a result of which a large amount of harmful pollutants was released into the atmosphere. Modern electronic models of high-pressure pumps demonstrate good efficiency, which allows diesel engines to meet strict environmental restrictions.
Injection pump device
With changes in the design of gasoline engines, a large number of varieties of fuel injection pumps appeared for them. Here are their main components:
- A fine filter is installed directly in front of the pump.
- The plunger piston and cylinder form a plunger pair.
- Through the recesses of the housing, fuel is supplied to the plunger pair.
- The camshaft with a centrifugal clutch is connected to the timing shaft via a belt drive.
- Plunger pair pusher drive.
- Plunger piston return springs.
- Supercharger system valves.
- Mode regulator connected to the accelerator pedal.
- Injection pump check valve (or return valve, through which excess fuel is supplied back to the main line).
- LNP (low pressure pump that pumps fuel into the injection pump).
The control systems of modern high-pressure pumps are becoming increasingly complex. Such pumps acquire their own electronic units, the operation of which is synchronized with the computer that controls the entire power unit of the car as a whole. In addition, modern injection pumps are equipped with their own electronic sensors and valves.
The vast majority of electronic fuel injection pumps have a diagnostic system, the operation of which allows the device to adapt to emerging malfunctions and failures. As a result, the pump can operate even if one of the sensors fails. However, if the electronic unit itself fails, the pump becomes completely non-functional.
Types of injection pump
Multi-plunger pumps
Their characteristic feature is the presence of individual plunger pairs for each cylinder (thus, injection is adjusted individually for each cylinder). Such pumps are divided into two types:
- V-shaped type – they are installed at an angle of 75-120 degrees in two rows;
- In-line – such pumps are mounted in a single-row version and are usually located together.
In in-line models, fuel is supplied to the injectors in a certain way using a mechanical drive. The cams control each plunger pair, ensuring their movement.
When the piston moves down, the fuel, on the contrary, is pulled up. As a result, pressure is formed, thanks to which diesel fuel is supplied to the nozzles.
The opening moment is determined by the electronic fuel injection pump control unit, which receives data from several sensors, in particular, from those that monitor the ratio of the crankshaft frequency and the position of the accelerator pedal.
In V-shaped pumps, the movement of the plungers is combined with the work of the racks acting on the bushing. This makes it possible to save space due to the higher rigidity of the structure itself, as well as due to the reduced dimensions of the cam shaft.
Distribution pumps
These fuel injection pump models are equipped with 1 or 2 plungers that supply fuel directly to the combustion chamber. The number of cylinders in this case can be from 4 to 12. This type of pump is common on diesel passenger cars, since they wear out quickly on truck engines. In addition, pumps of this design are very often installed on gasoline engines.
The plunger drive is represented by a cam mechanism of rotary, external drive and end-type types. The most common is the last option, since it requires only one plunger pair. External drive mechanisms have shown low reliability, and therefore they are practically not used anywhere. Rotary drives have one fuel supply section and 2-4 plunger pairs. There are no independent bushings here, and all other operating features are similar to the end-type drive.
Common Rail High Pressure Fuel Pump System
The Common Rail system collects diesel fuel in the fuel rail before sending it to the injectors. This fuel system involves the installation of up to 3 plunger units that create high pressure.
The movement of the plunger mechanism is ensured by the rotation of the shaft with an eccentric and springs. When the shaft turns, the cam presses on the spring, then on the piston, as a result of which the volume above the plunger increases, the pressure is rarefied, the valve opens and fuel is injected.
As the pressure increases, the valve closes, the plunger moves back, and the volume of fuel is reduced (when the desired pressure level is reached, it is pushed out to the nozzles after the special valve opens).
What pressure should be in the injection pump?
Specific performance characteristics depend on the operating mode of the motor of a given model. For any pump, the operating pressure is not a specific level, but an acceptable range. For example, some in-line diesel pumps generate pressures from 55 to 135 MPa. But in some models at idle, the lowest pressure reading can reach up to 15 MPa.
What pressure should be in the injection pump of a modern diesel engine?
Here you can judge by the technical indicators of main-line Common Rail pumps, which are capable of creating pressure up to 200 MPa; moreover, each subsequent development or modernization increases both the upper and lower limits of the range. The very first designs, such as the Bosch CP1, assumed operation in the range of 17-135 MPa, but the fourth generation model CP4 demonstrates the ability to create pressure from 23 to 200 MPa.
Gasoline engines are now equipped with direct fuel injection (GDI) systems. But here it is enough to provide a relatively low pressure – at the level of 3-11 MPa.
Measuring pressure in the injection pump
Here, you can do the following:
- Purchase a device for checking the fuel pressure in the line. This is a fuel pressure gauge kit with an adapter and drain (total cost of approximately 1.5 thousand rubles).
- Measure the pressure in the fuel line at a service station (cost – within 400 rubles).
- Measure the fuel pressure with a pneumatic pressure gauge to monitor the air pressure in the tires.
Let’s look at the last case in more detail using the VAZ 2110 as an example.
For any pressure gauge, the initial scale readings are highly inaccurate. This means that if the pneumomanometer scale has a range of 16-20 atmospheres, and the fuel pressure in the line is within 5-7 atmospheres, then any pressure measurements will be a priori inaccurate precisely because of the significant error in the initial part of the device scale. Therefore, fuel pressure can be determined only with a fuel meter (pressure gauge), whose measurement limit is 6-7 atmospheres.
To do this, you need to take a pressure gauge, wind plumbing flax directly under the pipe and put on an oxygen hose having an internal diameter of 9 mm. The hose must be secured with clamps.
Next, you need to place a rag on the generator (this is a fire-fighting measure to prevent the fuel from accidentally igniting, because the pressure must be measured with the engine running). Then the plastic cap on the fuel rail is unscrewed.
The second end of the hose is put on the ramp hole, where it is secured with a clamp. After this, start the engine and remove the hose from the ramp.
Signs of fuel injection pump failure
There are serious technical differences between different types of fuel injection pumps. This explains the difference in operational requirements. Firstly, for each pump you need to use a fuel that corresponds to this type of injection pump. Secondly, it is necessary to carry out regular high-quality, technologically advanced maintenance of pumps. And finally, thirdly, during operation you need to use only high-quality lubricants.
If at least one of the three listed conditions is not met, this will inevitably lead to the need for expensive and extremely labor-intensive repair work.
Most often, fuel injection pump defects lead to the following unpleasant effects:
- Significant increase in emissions;
- Fuel consumption increases;
- Engine power decreases;
- Various extraneous noises appear;
- It becomes difficult to start the engine;
- The operating frequency (number of revolutions) ceases to be stable – sometimes more, sometimes less.
However, a high-quality, original fuel injection pump that operates subject to mandatory operating conditions can last for many years without any breakdowns. The use of the recommended type of fuel guarantees reliable operation of both the fuel pumps and the entire engine as a whole, for at least the warranty period.
Nuances of diagnosing and repairing fuel injection pumps
Do not try to diagnose high-pressure fuel pumps in makeshift conditions. A modern fuel injection pump is a complex element of a power unit in its design and operating modes, which can and should be diagnosed exclusively on specialized stands in service stations.
Moreover, this procedure requires high qualifications from the employees who will be involved in its implementation. Timely diagnosis will make it possible to promptly identify and prevent:
- Violation of fuel pressure stability;
- Uneven fuel supply;
- Breakdowns of individual fuel injection pump parts due to wear, etc.
As a result, you will be able to save a lot on components, spare parts and repairs.
Often, the defect occurs not in the mechanical part of the injection pump, but in the electronic unit that controls it. A malfunction of this computer leads to the supply of incorrect signals to the device, resulting in failures in the fuel supply to the engine.
In this case, only a competent, highly qualified specialist can carry out a correct diagnosis. But attempts at handicraft replacement of parts can ultimately lead to larger-scale breakdowns of the entire power unit as a whole.
In general, timely maintenance and the use of standard fuels and lubricants (and mainly fuel) will save the operational life of the injection pump and ensure efficient operation of the engine.