Motronic 2.8.1
| Motronic 2.8.1 |
| Principle of operation |
The Motronic is an engine management system which controls both ignition timing and fuel injection from a single control module.
The Motronic 2.8.1 has sequential injection and individual control of ignition timing in connection with the occurrence of knocking in any of the cylinders. (This function is adaptive.)
Expressed in simplified terms, it could be said that the Motronic system is a combined electronic fuel injection system and electronic ignition system with knock sensor.
The fuel injection system has an advanced function in that injection is sequential. With regard to the ignition system, special mention may be made of the fact that the power stage is integrated with the control module.
| Control module, M2.8.1 |
Control module 510 monitors and controls a number of functions.
The control module obtains information from:
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Front oxygen sensor 136
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A/C via antifrost thermostat 171
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Front knock sensor 178
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Rear knock sensor 178A
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Engine coolant temperature sensor 202
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Throttle position sensor 203
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Mass air flow sensor 205
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Crankshaft position sensor 345
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Intake air temperature sensor 407
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Transmission control module (TCM) 502
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Rear oxygen sensor 515
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ABS control module 547
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Camshaft position sensor 555
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The control module sends information to:
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Fuel pump relay 102
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A/C compressor relay 156 (via pressure switch 166)
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Throttle position sensor 203
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Injectors 206
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Main relay 229
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Idle air control valve (IAC) 272
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EVAP canister purge valve 321
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Data link connector 445
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Main instrument display panel 540B (CHECK ENGINE and rpm)
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Secondary air injection pump 548
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Ignition coil unit 552
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| Power supply |
The system is supplied with positive voltage on relays 443 and 102 via fuse 17 when the ignition switch is in the Start or Drive position and with a constant power supply (+30 circuit) on relay 229 and the Motronic control module.
| Grounding |
The control module has a power ground (G7P), a lambda ground (G7L) and a signal ground (G7S). The grounding points are located on a metal bracket at the rear of the engine.
| Ignition system |
The ignition system consists of an ignition coil unit and HT cables.
The Motronic control module adjusts ignition timing on the basis of the following conditions:
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Engine speed
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Engine load
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Knock indication, if any
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| Data link connector 445 |
The data link connector for connecting an ISAT Scan Tool is located under the dashboard adjacent to the steering column (16-pin connector).
| Cars with automatic transmission |
The MOTRONIC control module obtains information on the current gear selector position, R-1-2-3-D, from the TCM control module.
Idling compensation takes place in gear selector positions R-D-1-2-3. Compensation is carried out by the control module opening the IAC valve to increase the air flow.
The first time R or D is selected, the control module is programmed for automatic transmission.
| Tachometer 110 |
Engine rpm signals are obtained from Motronic control module 510 so that engine rpm can be shown on the tachometer.
| Oxygen sensors 136 and 515 |
The oxygen sensors, one for the front cylinder bank and one for the rear cylinder bank, are mounted on the exhaust pipe. Their purpose is to provide the control module with information on the composition of the exhaust emissions (oxygen content).
Since the sensors continuously measure the oxygen content of the exhaust emissions, the control module can adjust the fuel-air mixture so that it is as close as possible to lambda = 1.
To work efficiently, the sensor must be hot. To attain operating temperature as quickly as possible, the sensors are fitted with a heating element known as a preheater.
| Air conditioning, A/C |
The Motronic control module receives information from the A/C switch/climate control unit, the ICE control module, antifrost thermostat 171 and pressure switch 166 to the effect that the A/C system is engaged. The control module then grounds A/C relay 156.
When the A/C compressor is engaged, the control module increases engine idling speed to compensate for the increased load represented by the compressor.
Grounding of the A/C relay is interrupted at wide open throttle, which results in disconnection of the A/C compressor for a few seconds. This has been discontinued on M94 models.
If the coolant temperature rises to 126°C, the ICE control module will break the connection to the anti-frost thermostat and the compressor will stop.
| Coolant temperature sensor 202 |
The coolant temperature sensor is of NTC type and supplies the control module with information on the temperature of the coolant.
If an open-circuit occurs, the control module will simulate a temperature of 80°C (176°F).
| Throttle position sensor 203 |
The throttle position sensor provides the control module with information on the position (angle) of the throttle butterfly.
The sensor gives the angle continuously from idling speed to wide open throttle.
| Malfunction indicator (CHECK ENGINE) lamp 47O |
The malfunction (CHECK ENGINE) lamp in main instrument display panel 540 lights up when serious and emission-related faults occur in the engine management system.
| Idle air control (IAC) valve 272 |
The idle air control valve is regulated by the control module which adjusts the opening angle of the valve to maintain idling speed constant.
For instance, this means that the valve opens so that idling speed (which would otherwise drop) is adjusted to compensate for the increased load when the A/C is switched on or DRIVE is engaged.
If a fault occurs in the circuit, the valve is automatically adjusted to a fixed idling speed of at least 1000 rpm.
| EVAP canister purge valve 321 |
The EVAP canister purge valve is located in the engine bay on the right-hand side. It is controlled by the control module on the basis of information on coolant temperature, engine speed and load.
The valve opens under specified conditions and allows the fuel vapours from the evaporative emission canister to pass into the intake manifold where they are burnt together with the regular fuel-air mixture.
| Crankshaft position sensor 345 |
The control module obtains information on the position and speed of the crankshaft from the crankshaft position sensor.
The sensor consists of a slotted ring on the crankshaft at the flywheel end and an inductive sensor mounted on the engine block.
The inductive sensor works somewhat like a small alternator, the sinusoidal voltage of which increases with increasing speed.
The sinusoidal voltage alternates between positive and negative polarity, which is brought about through alternating holes and "ribs" on the slotted ring.
This alternation of polarity is used by the control module for the transmission of pulses.
The control module can in this way identify which cylinder pair's pistons are at, or on the way up to, TDC.
If the sensor does not work or if there is no continuity in the circuit, the engine will not start.
| Camshaft position sensor 555 |
The camshaft position sensor is of Hall sensor type and, apart from the Hall sensor element, consists of a special "pimple" on the exhaust side camshaft in the front bank of cylinders.
When the camshaft is rotating and the "pimple" passes the Hall sensor, this indicates when cylinder 1 is ready for ignition.
| Mass air flow sensor 205 |
The mass air flow sensor measures the air mass consumed by the engine, which is proportional to the engine load.
If the sensor develops a fault, the control module obtains the necessary information from the throttle potentiometer.
| Knock sensors 178 and 178A |
The knock sensors, one for the front bank of cylinders and one for the rear bank, sense the engine's knocking tendencies and convert any knocking into a voltage which the control module processes to adjust the ignition timing so that optimum performance and emissions are obtained.
| Temperature sensor 407 |
The intake air temperature sensor is located in the intake manifold. It is of NTC type and provides the control module with continuous information on the temperature of the intake air.
Low temperature = High voltage High temperature = Low voltage
| Secondary air |
To get the catalytic converter working as soon as possible after a cold start, ambient air is pumped into the exhaust manifold where the oxygen in the air starts a chemical combustion process.
Once the engine has started, the secondary air injection pump starts up and a secondary air injection control valve opens the connection to the exhaust manifold. Operation is dependent on temperature and time.
The secondary air injection control valve closes and the pump stops after a maximum period of 80 seconds or when engine temperature reaches 65°C.
| Speed signal |
Wheel speed information comes from the ABS control module. This information is used to adjust idling speed to 800 rpm when road speed is 0 km/h.
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