High pressure fuel pump - how to ensure its stable operation?

A key structural unit of the injection system of a diesel engine is the high pressure fuel pump (TNFP).

The main elements and diagram of the high pressure fuel pump

The high-pressure fuel pump performs the task of supplying precisely measured volumes of automotive fuel to the diesel cylinders at a certain moment and under a certain pressure.

In other words, this device is responsible for the correct circulation of fuel through the fuel system.

According to the option of supplying high pressure, they are divided into units with accumulator injection and direct action. In the second case, the injection and injection processes take place at the same moment, and the required fuel spray pressure is provided by the movement of the plunger.

The main element of the injection pump is a plunger pair. It is a long piston, small in diameter (as a rule, the diameter of the device is several times smaller than its length), which fits as tightly as possible to the working cylinder. The gap between them (it is called precision conjugation) never exceeds 1-3 microns. The working cylinder contains inlet valves (two or one) through which fuel is supplied. Then it is pushed out through the exhaust valve by a plunger.

Structurally, pumps are divided into three types:

• distribution: 1 or 2 plungers are installed in it, which pump fuel and distribute it among the existing cylinders;
• in-line: has a separate plunger pair;
• trunk: they are responsible for pumping fuel into the battery.

Adjustment and repair of the high pressure fuel pump - process features

The need for repair of the injection pump can be caused by several reasons. The most common of them are considered to be the following:

• Pump wear. It is easy to determine it by such phenomena as loud and uneven operation of the engine, difficult starting it in a hot state, loss of power.
• Low quality application. Fuel is used for moving high-pressure fuel pump units as a lubricant. If it includes certain impurities (dirt particles, drops of gasoline or water), its lubricity is reduced, which causes the pump to fail.
• Incorrect operation of electronic devices installed on the vehicle.

When repairing an injection pump, it is most often necessary to change worn parts, and this can only be done by disassembling the device. In principle, it is not so difficult to carry out repair work yourself if you arm yourself with knowledge about the design of the fuel pump, as well as a set of special tools (vice, gas wrench, tweezers, a set of hexagons and heads, calipers, screwdriver). But experts always recommend trusting them to the masters of service stations and car services.

How is the injection pump adjusted?

Periodic adjustment of high pressure pumps is a mandatory procedure, without which the normal and reliable operation of the entire diesel engine is impossible. It is carried out on special stands (for example, on SDTA-1). The injection advance clutch is dismantled from the device (it operates in automatic mode), the cam shaft is coupled to the stand drive.

After that, the necessary checks are carried out, during which the uniformity and magnitude of the fuel supply, as well as the start of the supply, are adjusted. For these purposes, a special mechanism is used to drive the curtain. The latter is introduced between the measuring cylinders and the reference injectors at the moment when the supply is turned off, which prevents the fuel from entering the cylinders.

To control the start of supply, a momentoscope is used (a short piece of fuel line to which a glass tube is connected). And in order to adjust the moment of the start of the feed, adjusting bolts are used, which are screwed into the plunger pushers.