Multec System
Note: There are no conditions for adjusting or changing the idle speed; when checking the idle speed, remember that it can constantly change under the control of the ECU.
2. The Multec system is essentially a simple method of preparing the air/fuel mixture, replacing the carburetor with a single injector mounted in the throttle body. Therefore, this type of system is also called Throttle Body Injection (TBi), Central Fuel Injection (CFi) or Single (or Mono) Point Injection. The complete system is best explained by considering it as three subsystems: the fuel delivery system, the air metering system and the electric control system.
3. The fuel supply system consists of a fuel tank (with an electric fuel pump submerged inside), fuel filter, fuel injector and pressure regulator (installed in the throttle body), as well as hoses and tubes connecting all these units. With the ignition on (or when the engine is running, models with X16 SZ engine) the pump is supplied with power via the pump relay and fuse 11, under the control of the Electronic Control Unit (ECU). The pump pumps fuel through the fuel filter to the injector. The fuel pressure is controlled by the regulator, which, when the pressure increases, returns excess fuel to the tank.
4. The air flow measurement system contains the intake air temperature control subsystem and the air filter, but the main components are in the throttle body assembly. It contains the injector that injects fuel into the back of the throttle valve and the throttle potentiometer. The potentiometer is connected to the throttle shaft and transmits information to the ECU regarding the throttle valve opening degree by transmitting a changing voltage. The idle air quantity control stepper motor is controlled by the ECU and is designed to maintain the idle speed.
5. The electrical part of the fuel injection system consists of the ECU and all the sensors that supply the control system with information, plus the actuators that control the entire system. Note that the ignition system is controlled by the same ECU.
6. The manifold pressure sensor is connected to the intake manifold by a hose. Pressure changes in the intake manifold are converted into electrical signals that are used by the ECU to determine engine load. The operation of the throttle potentiometer has been explained previously.
7. Information regarding engine speed and crankshaft position comes from the distributor on models with the C16 NZ engine and from the crankshaft speed/position sensor on models with the C16 NZ2, X16 SZ and C18 NZ engines.
8. The odometer provides the ECU with information regarding the vehicle speed, and the coolant temperature sensor provides information regarding the engine temperature. The knock sensor is located in the cylinder block between cylinders 2 and 3 on XI6 SZ engines, and provides the ECU with additional information if it detects pre-ignition during the combustion process.
9. All these signals are compared by the ECU with the set values stored in the memory. Based on this information, the ECU selects the output values corresponding to these values. It controls the ignition amplifier unit, changing the ignition timing as required. The fuel injector is controlled by changing the open time, enriching or leaning the mixture, depending on the operating mode. The stepper motor, controlling the air, adjusts the idle speed. The fuel pump relay controls the fuel supply and the oxygen sensor. The mixture values, idle speed and ignition timing are constantly changed by the ECU, to improve starting and warming up the engine, to maintain idle speed, acceleration and smooth driving. The injectors are also switched off during engine braking to improve fuel economy and reduce exhaust emissions. Additionally, on X16 SZ engines, the ECU also controls the action of the carbon canister valve in the fuel vapor extraction system.
10. The oxygen sensor is screwed into the exhaust manifold, and the ECU has constant feedback. The unit, based on this data, constantly adjusts the mixture to provide the best conditions for the efficient operation of the catalytic converter.
11. Until the oxygen sensor is fully heated, there is no feedback and the ECU uses programmed values to determine the correct injector opening duration. When the sensor warms up to normal operating temperature, the tip (oxygen sensitive) sends a varying voltage to the ECU depending on the amount of oxygen in the exhaust. If the inlet air/fuel mixture is too rich, there is little oxygen in the exhaust and the sensor sends a low voltage signal. The voltage increases as the mixture becomes leaner and the amount of oxygen in the exhaust increases. Maximum conversion efficiency occurs when the inlet air/fuel mixture is maintained in the chemically correct ratio for complete combustion of gasoline 14.7 parts air to 1 part fuel (stoichiometric number). The sensor output voltage varies over a wide range, the ECU uses this variable signal to correct the inlet fuel-air mixture ratio by changing the fuel injector opening duration.
12. In addition, the ECU has a diagnostic mode, and can receive and transmit information through the diagnostic connector, so that it can perform diagnosis and tuning with Opel TECH1 test equipment.
Motronic system
13. The Motronic system has several different versions, depending on the model. The system is completely controlled by the Motronic engine management system (Section 5), which also controls the ignition timing.
14. Fuel is pumped from the rear-mounted fuel tank by an electric fuel pump located underneath the vehicle and passes through a pressure regulator to the fuel rail. The fuel rail is a reservoir for four fuel injectors, which inject fuel into the intake tracts of the cylinders. On single overhead camshaft engines, the fuel injectors receive a single pulse, opening them simultaneously once per crankshaft revolution. On double overhead camshaft engines, a sequential fuel injection system is used, whereby each injector receives its own electrical pulse and the four injectors operate independently, providing more precise control of fuel delivery to each cylinder. The duration of the electrical pulse determines the amount of fuel injected, the pulse duration is calculated by the Motronic unit based on information received from various sensors.
15. On single overhead camshaft engines, the intake air passes from the air filter to the air flow meter and then through the throttle valve to the cylinder intake tracts. A flap in the air flow meter deflects depending on the strength of the air flow: this deflection is converted into an electrical signal and goes to the Motronic unit. A potentiometer screw on the air flow meter allows adjustment of the idle mixture by changing the reference voltage going to the Motronic unit.
16. On DOHC engines, the intake air passes from the air cleaner to the air flow meter (a wire through which a current of some voltage flows), and then through the two-position throttle body assembly to the intake tracts of the cylinders. The electrical current required to maintain a constant wire temperature in the air flow meter is proportional to the mass of the air flow cooling the wire. The current is converted into a signal that goes to the Motronic unit. The throttle body contains two flaps that gradually open. The potentiometer screw located on the air flow meter allows you to adjust the idle mixture by changing the reference voltage going to the Motronic unit.
17. The throttle position sensor enables the Motronic unit to calculate the position of the throttle valve and, on some models, the degree to which it is opened. This allows additional fuel to be supplied during acceleration when the throttle valve is suddenly opened. Information from the throttle position sensor is also used to cut off fuel supply during engine braking, thus improving fuel economy and reducing harmful emissions.
18. The idle speed is controlled by a variable orifice valve that regulates the amount of air supplied bypassing the throttle valve. The valve is controlled by the Motronic unit; and direct adjustment of the idle speed is not possible.
19. Additional sensors provide the Motronic unit with information on coolant temperature, air temperature and, on models with a catalytic converter, the oxygen content in the exhaust gas.
20. The fuel filter is built into the fuel supply line, cleaning the fuel before it is supplied to the injectors.
21. The fuel pump cut-off relay is controlled by the Motronic unit, which cuts off the supply voltage to the fuel pump, causing the engine to shut off with the ignition on if any fault occurs. All models from 1993 onwards are equipped with Motronic systems, the fuel pump is located inside the fuel tank.
22. Late M2.8 system - basically the same as early M2.5 system except for the following:
- a) Air mass flow tape meter - the previously used unit with a live wire has been replaced by an air mass flow tape meter on the M2.8 system. Its operating principle is similar to the old one, except that a thin electrically heated plate is used instead of a wire. A constant plate temperature is maintained by an electric current, which varies depending on the mass of the inlet air passing by the plate. The current required to maintain a constant plate temperature is proportional to the mass of the inlet air flow. The current is converted into a signal that is sent to the Motronic unit.
- b) Inlet Air Temperature Sensor - located in the hose between the air mass flow tape and the air cleaner, and is designed to accurately monitor the inlet air temperature. The signals from this sensor, in combination with other sensors, are used to determine the hot start condition. The Motronic unit then processes these signals and changes the duration of the injector open state.
- c) Throttle potentiometer on the M2.8 system The throttle potentiometer replaces the throttle switch used on earlier models.
Simtec System
23. Instead of mechanical parts, a large number of electronic components are used: sensors and actuators with the Simtec engine management system. They provide more accurate data, as well as a greater ability to freely control engine modes.
24. The control unit is equipped with an electronic ignition control system called the Microprocessor Controlled Inductive Control System ("Microprocessor Spark Timing System, inductive triggered" or MSTS-i), and components such as a mechanical ignition distributor are no longer needed. The control unit is located behind the trim panel, in the footwell on the right (door pillar).
25. The ignition coil has been replaced with a dual coil, which is switched by the control unit.
26. The camshaft sensor indicates a certain position when the crankshaft passes the inductive head. It is designed to determine TDC ("Top Dead Center"), the crankshaft angle and the engine speed. The signals are used by the control unit to calculate the ignition timing and for the fuel injection system.
27. The air mass flow tape measure determines the mass of air entering the engine. The system uses this information to calculate the correct amount of fuel to inject into the engine.
28. The intake air temperature sensor (NTC) is installed in the intake air duct between the air filter and the warm air flow meter.
29. The carbon filter control valve is actuated by the system. The tank ventilation is checked by the lambda control (or oxygen sensor) and is adjusted by the control unit computer.
30. There is also a detonation control system. It eliminates the need for octane adjustment, this is done automatically by the control unit.
31. This engine is also equipped with an exhaust gas recirculation valve (re-burning of exhaust gases) and secondary air injection (AIR - Air Injection Reactor), all of which comply with the latest European exhaust emission standards (since 1996). The system returns a certain amount of exhaust gas to the combustion tract. As a result, the formation of nitrogen oxides (NOx) is reduced. The secondary air injection system has a supercharger that introduces air into the exhaust manifold, reducing the content of CO and HC in the exhaust gases.
Visitor comments