Peculiarities
The high-pressure direct injection system with a common rail provides a metered supply of fuel at a certain point in time.
The system includes:
- low pressure pump located between the suction unit and the fuel filter for the F9Q 754 engine with high pressure fuel pump CP1;
- manual fuel priming pump located between the suction unit and the fuel filter for the F9Q 750 engine with high pressure fuel pump SRZ;
- fuel filter;
- - fuel injection pump;
- TN8D, with built-in suction pump (SRH);
- high pressure regulator attached to the pump (fixed on high-pressure fuel pump SRZ);
- fuel rail, fuel pressure sensor and pressure limiter;
- four electromagnetic nozzles;
- sensors;
- injection computer.
Attention! Disassembly of high pressure fuel pump and injectors is prohibited.
Operating principle
The common rail high-pressure direct injection system is a sequential injection system that operates on the principle of port injection systems of gasoline engines.
This new injection system, thanks to its pre-injection method, reduces engine noise, reduces the content of particulate matter and toxic gases in the exhaust gases and achieves a significant increase in engine torque, starting from low speeds.
The injection pump delivers fuel at high pressure to the fuel rail. The high pressure regulator installed on the pump modulates the high pressure value according to the ECU commands. From the fuel rail, fuel is supplied to the injectors through steel fuel lines.
injection computer:
- determines the amount of injection pressure necessary for the normal operation of the engine, and sends the appropriate signals to the pressure regulator. It controls the pressure value based on the analysis of the signal values of the fuel pressure sensor installed on the fuel distribution rail;
- determines the injection duration required to supply a sufficient amount of fuel, and the injection start time;
- after determining these two values, it individually controls the operation of each injector by applying electrical signals.
The amount of fuel supplied to the engine is determined depending on:
- the duration of the control signal to the injector;
- injector valve opening and closing speeds;
- injector valve needle stroke (depends on the type of injectors used);
- hydraulic performance injector (depends on the type of injectors used);
- rail pressure controlled by the injection computer.
Post-repair inspection
F9Q 750 engine
Fill the system with fuel using the manual priming pump located on the engine.
F9Q 754 engine
A cock is installed on the fuel filter at the point of connection of the fuel return pipeline to the fuel tank.
During normal engine operation, the valve should be in the open position.
However, if it is necessary to fill the system with fuel after work has been carried out, the fuel filter has been replaced, or in the event of a fuel failure (when fully developed) perform the following operations:
- close the tap on the fuel filter;
- actuate the low pressure fuel pump by placing the card in the reader several times in the 1st fixed position;
- start the engine;
- turn on the faucet (in the open position of the valve, the two colored marks are aligned).
Note. Some vehicles do not have this valve. In this case, the above operations are not performed.
After performing any work, check that there are no fuel leaks. Let the engine idle until the electric fan of the cooling system turns on, then increase the engine idle speed several times.
Attention! Do not use fuel containing more than 10% diester.
The system provides fuel injection under pressure up to 1350 bar. Before carrying out any work, make sure that there is no pressure in the fuel rail.
The following tightening torques must be strictly adhered to:
- high pressure fuel lines;
- nozzles, when screwed into the cylinder head;
- pressure regulator (on the F9Q 750 engine with high pressure fuel pump SRZ, the regulator is fixed);
- fuel pressure sensor.
When performing repair work or removing the injection pump, injectors, supply and return fuel lines, high pressure fuel lines, it is necessary to plug the holes with new plugs of the appropriate diameter to protect against contamination.
Replacement of high pressure fuel lines must be carried out in the following order.
Remove the tubing to be replaced.
Close the openings with safety plugs.
Loosen the fuel rail mounting bolts.
Install the high pressure pipe.
Tighten the fuel line to injector fitting to the specified torque.
Tighten the union of fastening of the pipeline to a fuel-distributing rail to the specified moment.
Tighten the fuel rail mounting bolts to the specified torque.
Tighten to the specified torque the connection of the pipeline going from the injection pump to the rail (first on injection pump).
Attention! Disassembly of the injection pump is prohibited.
When removing the injection pump, it is necessary to replace the fuel return line connected to the injectors.
The fuel temperature sensor is non-removable. It is integral with the fuel return rail.
Do not loosen the high pressure fuel line fittings while the engine is running.
It is forbidden to remove the pressure regulator on an F9Q 750 engine equipped with a high pressure fuel pump SRZ.
Possible consequences of contaminants entering the system
The system is very sensitive to contamination. The ingress of contaminants can lead to damage or complete failure of the high pressure injection system, seizing or depressurization of system elements.
All after-sales service work on the system must be carried out under conditions of complete cleanliness. Performing work in conditions of complete cleanliness means preventing the ingress of any contaminants (particles as small as a few microns) into the injection system when it is dismantled or into the fuel supply system through the fuel line connections.
Following the cleanliness guidelines applies to the entire system, from the fuel filter to the injectors.
The source of pollution are:
- metal or plastic shavings;
- painting materials;
- various fibers;
- foreign objects, such as hair;
- polluted air, etc.
Attention! It is forbidden to wash the engine with a high-pressure jet, because. doing so may damage the wiring connectors. In addition, moisture can get inside the connectors, which can cause damage to the electrical circuits.
Before working on the injection system of diesel engines, make sure that there is a supply of plugs to protect the detachable connections. The plugs are disposable. Used plugs should be thrown away (they become contaminated after use and cannot be recycled by cleaning). Unused plugs should also be thrown away.
Make sure you have plastic bags with airtight seals for storing dismantled parts. With this method of storage, the likelihood of contamination of parts is reduced. Packages are also disposable, used packages are thrown away.
Make sure you have lint-free wipes available. The use of rags or plain paper for cleaning is prohibited. These materials leave behind fibers that contaminate the fuel system. Each wipe is used only once.
Cleaning parts before any disconnection of fuel lines
Use fresh thinner each time you work (used thinner contains impurities) Dispense thinner only into a clean container.
Use a clean and suitable brush for each job (the brush should not leave hairs).
Clean the detachable fittings with a brush and solvent.
Blow clean surfaces with compressed air (tools, work table and parts, fittings and installation locations for injection system elements). Make sure there are no brush hairs.
Wash hands before work and, if necessary, during work.
When working with protective gloves, wear rubber gloves over leather gloves.
Immediately after disconnecting the fuel lines, be sure to plug the openings through which contaminants can enter. The plugs required for this are available from the spare parts warehouse. Reuse of plugs is prohibited.
Seal the bag tightly, even if you have to open it again soon. The ambient air is one of the pollution factors.
Any removed element of the injection system after plugging the holes should be stored in a sealed plastic bag.
After disconnecting the fuel lines, the use of brushes, solvent, a directed jet of compressed air, brushes, ordinary rags for cleaning purposes is strictly prohibited. These cleaning methods may introduce contaminants into the system.
If any element is replaced with a new one, it should be removed from the package immediately before installation on the vehicle.