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Diesel engine fuel pump


  • High Pressure Line Pump (PE)
  • Rotary Distribution Pump (VE)
  • Adjusting the Rotary Manifold Pump
  • Electronically controlled dividing pumps
  • Malfunctions due to prolonged standstill

High Pressure Line Pump (PE):
The high-pressure line pump represents the first generation of diesel fuel pumps. A high-pressure line pump consists of as many plunger elements as there are cylinders. Each plunger supplies the fuel for its own cylinder. The high pressure plungers are actuated by the internal pump camshaft. When these plungers are pushed up, they cause the discharge stroke (forcing diesel through the line to the cylinder). The high-pressure inline pump operates with a fixed stroke. The fuel delivery is controlled by the rotation of the plungers. This rotation is performed by the control rod, which is indirectly connected to the accelerator pedal. When the accelerator pedal is pressed, the plungers are rotated, thereby regulating the fuel flow.

The pump also houses the governor (visible in the illustrations below), which, among other things, ensures that the diesel engine's idling speed is kept as stable as possible, and that the fuel delivery is adjusted as the engine speed increases.

An in-line pump suffers from internal leakage losses. The leakage losses are mainly due to imperfections in the cylinder seal: the cylinder wall can be microscopically uneven, leaving room for leakage past the piston. At lower speeds and low pressure levels, small amounts of diesel fuel may leak past the seals of the plungers or other internal components. It can occur because the seals do not close perfectly or wear over time.

As the pump speed increases, the pressure inside the pump tends to increase. This higher pressure can help reduce imperfections in the seals and components, which can reduce leakage losses. This is because the higher pressure pushes the seals against the moving parts and reduces the chance of leakage.

Line pump
Fuel Flow Control Plunger

When the fuel supply is not properly regulated, so that too much fuel is injected to the engine, this can lead to a too high trim speed. 

  • If there is a fault in the fuel control of the in-line pump, the plungers may inject more fuel than is required for the current RPM. This can lead to an excessive combustion rate and a higher than recommended engine speed;
  • If the control rod responsible for adjusting the fuel flow fails, the in-line pump may not be able to respond correctly to the accelerator pedal. This can result in an unintentional increase in fuel delivery and thus engine speed;
  • Physical faults in the in-line pump, such as stuck plungers, damaged components, or mechanical blockages, can disrupt normal fuel flow control and possibly cause uncontrolled engine speed.

Rotary Distribution Pump (VE):
The rotary distribution pump (the CAV DPA and the Bosch VE) was developed as a successor to the high-pressure line pump. This fuel pump works entirely mechanically. The advantage of the rotary distribution pump compared to the line pump is the reduced number of plungers (and thus the built-in size) and the standard injection adjustment.

Bosch VE pump:
The rotary distribution pump from Bosch is a fully mechanical pump. The lever on the pump is directly connected to the accelerator pedal. The pump works with a plunger that moves axially. The plunger makes both a rotating and a reciprocating movement (explained in detail below). The control slide (connected to the accelerator pedal) and the centrifugal regulator ensure the correct fuel metering. When the control valve shifts to the left, fuel can leave the pump through the return port, reducing the amount of fuel. When more fuel is needed (higher rpm or load), the control slide moves further to the right, increasing the fuel volume to the injectors. With the same engine load, the speed increases as a result.

Cross-section of the Bosch VE pump

The plunger in the Bosch VE rotary pump is responsible for feeding, injecting and distributing the fuel. These 3 steps are explained below using the three illustrations.

1. Supplying the fuel:
The plunger is turned to the left, so that the fuel – originating from the feed pump – can flow via the inlet channel above the plunger to the pressure chamber to the right of the plunger. 

2. Injecting the fuel:
The cam disc pushes the plunger to the right. The inlet channel to the press space is thus closed off and the volume in the press space is reduced. The pressure on the fuel increases until a connection with the exhaust duct is established by twisting. There is an outlet every 90 degrees, through which the fuel flows under pressure.

3. Dosing the amount of fuel:
The position of the control slide determines the end of the injection, and thus the amount of fuel that is fed to the injector via the outlet.
The position of the control slide is determined by the centrifugal controller. This part is described below.

Centrifugal regulator:
The accelerator pedal is indirectly connected via spring 4 and the lever assembly (6, 7, 8, 9) with control slide 10. In the position shown (left), the accelerator pedal is fully depressed and the control slide will want to move to the right for maximum flow. M2 is the pivot point. When the speed to be regulated is reached, the centrifugal force will want to move the control sleeve II to the right, causing the control slide 10 to move to the left. An equilibrium situation thus arises between the spring 4 and the centrifugal force. The speed is regulated by the flow control. 

The right image shows the regulation at idle speed. The accelerator pedal is not depressed and the lever is fully in the right-hand position. A weak spring (14) now ensures the equilibrium situation.

Left: accelerator pedal depressed. Right: accelerator pedal not pressed, engine idle speed.

Injection advance:
Rotary fuel pumps are always equipped with injection advance as standard. When increasing the speed, it will be necessary to inject earlier in order to have a good power stroke. Otherwise, the diesel mist injected by the injector will not have enough time to mix well with the air at a higher speed. The injector will therefore always have to inject a few degrees before TDC (Top Dead Center) earlier at an increasing speed. The injection advance system consists of a plunger connected to a roller ring. At an increasing speed, this roller ring is rotated in the direction of rotation, so that the injection plunger starts earlier with the pump stroke (and thus the injection). No electronics are used for this injection advance.

Injection advance control VE pump

Adjusting the rotary distribution pump:
It is important that the pressure build-up in the pump takes place at the right time. The pressure build-up determines the injection time of the diesel fuel through the injectors. The position of the fuel pump can be changed in relation to the engine block. There are slots in the engine block in which the fuel pump can be moved. Rotating the pump will not affect the gear driven by the timing belt. The gear remains stationary, but the pump behind it changes position. For a distribution that rotates clockwise (clockwise), the following applies:

  • Moving the pump counterclockwise will result in earlier injection;
  • Moving the pump clockwise will result in a later injection;
    The fuel pump must therefore be adjusted on the basis of the crankshaft position and the position of the control slide. This should be done with a dial indicator.

Below is a step-by-step plan with which a rotary distribution pump can be adjusted.

1. Place the piston of cylinder 1 at TDC.
Rotate the crankshaft until the piston of cylinder 1 is at top dead center.

You can tell if the crankshaft timing is correct by looking for the mark on the flywheel that matches the mark in the gearbox housing.

2. Timing of the fuel pump
Check that the fuel pump timing is correct. The two marks (marked in white in the picture) must face each other. If the fuel pump is not on time, the timing belt must be removed and fitted correctly.
Then insert the locking pin (in the picture in the hole with the red arrow).

3. Disassembling parts
Disassemble the fuel lines, coolant hose and thermostat housing to create space behind the fuel pump. You need this space to be able to mount the dial indicator in the pump.

4. Dial indicator
Locate the dial indicator with which the fuel pump should be adjusted.
Screw the individual parts of the dial indicator together. Remove the blind plug in the fuel pump and screw in the dial indicator. Make it easy on yourself by positioning the dial indicator so that it is clearly visible when the crankshaft is turned.

4. Set a preload.
Because you want the needle of the dial indicator to always touch the pump internally, you set a preload. This pushes the dial indicator a little further into the pump housing.
Set this tension to at least 2 millimeters (see picture).

5. Rotate the crankshaft in the normal direction of rotation.
The crankshaft must be turned. The pointer of the dial indicator will move. Because the distribution plunger makes a reciprocating movement, the pointer will stop at some point. When turning the crankshaft further, the pointer will move back again.
At the point at which the pointer stops, the maximum stroke of the distribution plunger has been reached.

6. Set the dial indicator to 0.
Turn the black ring on the dial indicator and set it to 0.

7. Place cylinder 1 piston at TDC.
Rotate the crankshaft again until cylinder 1 piston is at TDC. Again, check the marks on the flywheel and gearbox housing.
Read the value on the dial indicator that the pointer indicates. The pointer has moved counterclockwise. That means the distributor plunger has made a stroke of
0,70mm. Compare this value with the factory values. If the values ​​match, nothing needs to be adjusted. If the value is incorrect, the pump must be adjusted.

8. Adjust fuel pump.
Adjust the fuel pump by loosening the three bolts (shown in the illustrations) and shifting the position of the pump on the engine block.

Electronically controlled distributor pumps:
Today, just like petrol engines, diesel engines are controlled by an ECU (a control computer). With the help of this computer, various functions of the high-pressure fuel pump can also be controlled and the fuel dosage can be adjusted even more accurately than with a fully mechanical fuel pump. The electronically controlled distributor pumps are divided into the following three types:

  • Lucas EPIC pump
  • Bosch VP/VR pump
  • Bosch VP44

Lucas EPIC pump:
The Lucas EPIC pump is a fully electronically controlled rotary fuel pump. The following functions are controlled; starting output, idling speed control, part load output control, full load control, injection timing control, self-diagnosis.

Bosch VP pump:
The Bosch VP pump is internally similar to the mechanical VE pump, described earlier on this page. The parts such as the feed pump, the cam ring, the control valve, the pump manifold housing and the pump plunger are unchanged.

Compared to the VR pump, the VP pump has the following new parts:

  • Adjusting unit (actuator) for adjusting the position of the control slide.
  • Sensor to determine the position of the control slide.
  • Injection torque adjuster; this is controlled via a PWM signal. (PWM stands for Pulse-With modulation). The PWM signal comes from the ECU.

The adjustment unit adjusts the position of the control slide. This is done by working with a permanent magnet and an electromagnet that is controlled with a duty cycle. When the electromagnet is supplied with voltage by the ECU, it will become magnetic and will want to pull towards the permanent magnet. The longer the duty-cycle signal, the more magnetism is created and therefore a greater movement (adjustment) it makes. When the duty cycle signal is lost, the spring will retract the adjuster.
The position sensor is an inductive sensor, which monitors the rotation of the shaft of the aforementioned control slide. In this way the ECU has feedback that the desired positions have also been reached.

Injection advance:
The injection advance system is similar to that of the Bosch VE pump. Only with this VP pump the advance is controlled by a PWM signal from the ECU. In short, the ECU determines the position of the roller ring and not the speed of the engine, as was the case with the VE pump.

 The position of the roller ring regulates the injection moment. The position of the plunger determines the rotation of the roller ring. The plunger is pushed to the left against the spring force by a fuel pressure that allows the pressure regulator into the pump housing.
Through the fuel pressure regulator, the fuel under pressure continues to the return. As soon as the ECU gives a signal, this controller ensures that the internal supply is opened slightly more or less. When the supply is open, a fuel pressure flows into the pump housing, causing the entire plunger to move to the left against the spring force. This causes the roller ring to be turned to the right (clockwise). This means that the roller ring is turned in the “early” direction. The injection now takes place earlier before TDC. As soon as the fuel pressure in the pump housing falls, the spring ensures that the plunger returns to its starting position. The roller ring thus moves to "late" again.

Bosch VP44 pump:
As with the VE and VP pumps, the radial VP44 pump does not have the pump plungers in the longitudinal direction of the shaft, but transversely to the drive shaft. This high-pressure pump also sucks in the fuel itself and regulates the injection advance. The maximum injection pressure is max. 1850 bar.

When the pump is running, the plungers are pushed in by the cams on the cam ring. When the solenoid valve is closed, the pressure can build up and the connection to one of the injectors is made by turning the distributor shaft. That is when the injection takes place.

Malfunctions due to prolonged standstill:
With prolonged engine standstill can in some cases lead to problems with the fuel pump and fuel system. Here are some possible scenarios where prolonged downtime can have an impact:

  • Fuel degradation: If the fuel is left standing for an extended period of time, it can degrade and cause condensation. This can lead to the formation of sediments and impurities in the fuel that can eventually clog the fuel pump and injectors;
  • Evaporation and Resin Formation: As fuel vaporizes in the fuel lines, it can leave resinous deposits that can impede the free flow of fuel;
  • Seals and rubber components: Prolonged downtime can cause the seals, gaskets and rubber components in the fuel system to dry out and harden. This may cause leaks or compromise the sealing of the system;
  • Moving parts stuck: Oxidation and contaminants can cause moving parts to get stuck in the fuel pump. This can prevent the pump from building up the necessary fuel pressure.

To avoid this kind of problem during long periods of standstill, it is advisable to take precautions such as using fuel additives, not parking the car with a low fuel level to prevent condensation from forming in the tank, regularly running the engine to keep everything lubricated.