PRE-RELEASE
Detailed description, fuel system
| Detailed description, fuel system |
| Fuel tank |
The fuel tank is made of plastic and holds 58-litres. The feed pump is integrated in the fuel tank and there is an electric feed pump in the fuel tank that supplies fuel to the high pressure pump.
| Feed pump integrated in fuel tank |
An electric feed pump is mounted in the fuel tank that supplies fuel to the high pressure pump. The fuel pressure is 4 bar.
| Fuel lines |
The delivery line is for supplying fuel to the high-pressure pump and the return line for the return fuel. Both lines are made of plastic and steel.
| Fuel filter |
The fuel filter is used to filter and separate water from the fuel. The filter housing also contains a sensor to detect whether there is water in the fuel, preheating element, and a sensor for the fuel temperature.
If the filter should be full of water, the drive will be made aware of it with a message shown on SID: Water in Fuel, Contact Service. The fuel filter contains an exchangeable filter element.
| High-pressure pump |
The three-cylinder high pressure pump delivers the injection pressure, which can be up to 160 MPa (1600 bar). As the fuel requirement of the engine varies over a wide range, the fuel pressure delivered by the high pressure pump to the fuel rail must be regulated. This is done with the fuel regulator valve (652b) mounted on the high pressure pump and the fuel pressure regulator valve (652a) located on the right-hand side of the fuel rail.
The fuel regulator valve (652b) on the high pressure pump is used to restrict the supply of fuel to the inlet side of the pump. If fuel requirements are low, the pump supply will be restricted so the cylinders are not completely filled. Pump capacity is consequently regulated so that its power requirements are reduced. Regulation, using the valve (652b), is mainly carried out at engine speeds just above idling. The high pressure pump is driven by the timing gear at a fixed ratio to the crankshaft. This must be observed when changing timing belt or high pressure pump.
| Fuel quantity control valve, high-pressure pump (652b) |
The fuel regulator valve (652b) controls the amount of fuel to the high pressure pump. In this way, the high pressure pump can be prevented from running "flat out" (with full pump chamber) when fuel requirements are low. ECM controls the valve and measures the result in the form of attained fuel pressure in the fuel rail. If necessary, the PWM signal to attain requested pressure will be corrected. The valve mounted on the high pressure pump cannot be changed separately at present. If there is a fault with the valve, the whole unit comprising the high pressure pump with valve must be changed.
| Fuel rail/reservoir |
The fuel rail/reservoir is used to distribute the fuel to the four cylinders and acts as a reservoir to reduce pulsation. The fuel rail has connections for the high-pressure fuel from the high-pressure pump and the return fuel. A pressure sensor is mounted on the left-hand side of the fuel rail. Mounted on the right-hand side is the fuel pressure control valve (652a). The volume in the fuel rail is about 20 cm 3 .
16V:
8V:
The volume, shape and location of connections have been tested thoroughly to avoid problems with pulsating fuel pressure, which would cause uneven distribution of fuel to the four nozzles.
| Fuel pressure control valve, fuel rail (652a) |
The pressure sensor (652a) is mounted on the right-hand side of the fuel rail. It is used to regulate the pressure in the fuel rail and to control ECM.
16V:
8V:
| Fuel pressure sensor, fuel rail (653) |
The fuel pressure sensor (653) is mounted on the left-hand side of the fuel rail. It measures the fuel pressure so that the engine management system is aware when the requested pressure has been attained. It is controlled by ECM with +5V and the output voltage is within range 0.5-4.5V. When changing the pressure sensor, the diagnostic tool must be connected to reset adaptation values. Select Menu - Engine - Engine management system - Adjustment - Fuel Pressure Sensor Replaced.
16V:
8V:
| High-pressure pipe |
The high pressure pipe is a connection pipe between the fuel rail and the injector. It is made of steel.
16V:
8V:
| Injectors |
Electrically controlled injectors (206a-d) that inject fuel into the combustion chamber. The injectors have six holes, giving six jets of fuel on the Z19DT. The Z19DTH has seven holes. The holes through which the fuel is injected has a diameter of 0.145 mm (Z19DT), 0.141 (Z19DTH). As a comparison, a normal strand of hair is 0.08 mm. The holes must be very small so that the fuel will atomise into small drops. Certain manufacturing tolerances are just a few thousandths of a millimetre. Consequently, it is essential that dirt does not enter into the fuel system.
The injectors a low-ohmic and controlled by ECM according to the peak and hold principle. This means that an opening pulse is sent first with a rather high current (peak) in order to obtain a rapid response from the injector. After a certain period of time, the nozzle is assumed to be open and the current will be limited by ECM (hold). ECM can inject fuel up to five times per working stroke with a maximum injection timing of around 1 ms. That is faster than a wink of the eye.
The injection volume is, for example, about 1 mm 3 for the pilot injection, to be compared with a drop of water that is around 30 mm 3 . Consequently, the injector must be regarded as a precision instrument.
| Important | ||
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If the injectors are to be refitted, mark the injectors so that they can be refitted to the same cylinder. |
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| Important | ||
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If new injectors are to be fitted, read and make a note of its classification code. The code is to be used when programming using the diagnostic tool. |
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16V:
8V:
The injectors are given a final check after manufacture and receive a classification code depending on their characteristics. This code describes the nozzle characteristics for the control module. In case of a change of injector, the diagnostic tool must be connected for programming. Select Menu - Engine - Engine management system - Adjustment - Injector Replaced. The classification code must then be specified.
| Return hoses/pipes |
The hoses are used to handle the return fuel from the injectors. A controlled leakage occurs in the injectors and passes back to the fuel tank via the fuel return hoses, return fuel container and then to the return fuel line.
16V:
8V:
| Return fuel container |
The container where the return fuel from the high-pressure pump, fuel rail and injectors is collected. Running from the return fuel container is a line to the fuel tank, the return line. Of the fuel delivered by the high-pressure pump, about three quarters of it passes back via the return fuel container.
16V:
8V:
| Function description |
Mounted in the 58-litre fuel tank is the fuel pump unit. It comprises a feed pump (323) that presses fuel to the high-pressure pump and a fuel level sensor (46) that is connected to ECM (595).
The feed pump is mounted in a container from which it draws fuel. The container fills with fuel using an ejector pump driven by the return fuel flow. This is to ensure the container is always full so that the feed pump does not run empty and draw air, e.g. when lurching hard.
When the key is turned to "ON", ECM activates the fuel pump relay (102) during the glow duration plus a further 15 seconds to build up fuel pressure. The fuel pump will subsequently stop, ECM will activate the relay when the crankshaft starts to rotate. Fuel with a pressure of around 4 bar is now fed via the fuel line to the fuel filter, where the fuel is filtered and any water separated. If necessary, ECM will heat the fuel.
ECM measures the temperature using the fuel temperature sensor (651). Inside the fuel filter is a preheating element powered via the preheating relay (641), which ECM activates for preheating. If the filter is full of water, it must be drained and the driver will be made aware of this with the SID message: Water in Fuel, Contact Service.
Fuel passes from the fuel filter to the high-pressure pump. The inlet to the high-pressure pump has a fuel regulator valve (652b) used to regulate the fill factor of the high-pressure pump element. The fuel regulator valve (652b) is controlled by ECM with a PWM voltage. Since the engine fuel requirements vary over a large range, the fuel pressure supplied by the high-pressure pump to the fuel rail must be regulated. This is done by the fuel control valve (652b) and the fuel pressure control valve (652a), and is measured by the fuel pressure sensor (653).
When starting the engine, the high-pressure pump is allowed to deliver as much as it can to ensure quick and reliable starting. The fuel control valve (652b) is then fully open and fuel pressure regulation is then handled by the fuel pressure control valve (652a).
When the engine is running just faster than idling, the fuel pressure is regulated with the fuel control valve (652b) and the fuel pressure control valve (652a). By allowing both valves to work it is possible to prevent pulsations caused by uneven fill factor in the high pressure pump element. The pump is allowed to work at a relatively high fill factor and the fuel pressure control valve (652a) dumps fuel so that the correct fuel pressure is attained.
At a slightly higher engine speed fuel pressure regulation is handled by the fuel control valve (652b). By not allowing the pump to run at full fill factor, the torque requirement for the high-pressure pump will be reduced. A reduced torque requirement gives a lower fuel consumption as the load on the engine is lower. If rapid drops in pressure are required, the fuel pressure control valve (652a) will dump fuel to reduce pressure quickly. Depending on the driving conditions, the fuel pressure can go up to 160 Mpa (1600 bar).
The fuel from the high-pressure pump passes via a steel pipe to the fuel rail. This is made of steel and has a value of 20 cm 3 . The volume, shape and location of connections have been tested thoroughly to avoid problems with pulsating fuel pressure, which would cause uneven distribution of fuel to the four nozzles.
From the fuel rail, fuel passes to the injectors via steel pipes. The length of the pipes are all the same to prevent phenomena such as uneven fuel distribution.
The injectors are mounted in the cylinder head and fuel is injected centrally into the combustion chamber. The combination of six holes in the nozzle, centrally located injectors and the shape of the combustion changer offers a good mixture of fuel in the air.
ECM controls the opening duration of the injector and the timing (crankshaft position). Maximum opening duration is in the region of 1 ms. The injectors are controlled directly by ECM, which also calculates the injected quantity using the requested torque as main parameter. The request comes from the accelerator pedal (379), for example, or the cruise control and a number of internal compensations then add or subtract torque. The result is a total torque request that is converted to injection timing. Meanwhile, ECM calculates the necessary air mass that is required for the fuel quantity in question so that the engine can deliver high output with low fuel consumption and low emissions. This request is sent to turbo control. If the air mass is below the smoke level, the injected fuel quantity will be reduced until the air mass exceeds the smoke limit.
