Computers and Control Systems: Description and Operation

DME Control Unit Operation:

Digital motor electronics (DME) is used to control engine operation. Fuel is delivered to the engine via a Bosch L-Jetronic electronic fuel injection system. Using sensor input, it is able to monitor engine speed, load, temperature, and fuel mixture. These inputs are applied to preprogrammed "maps" to determine output characteristics necessary for optimum fuel economy and performance.

DME for 911 includes:
^ Control unit with 55-pin plug connection and self-diagnosis.
^ Sequential fuel injection, knock regulation, resonance intake and double ignition.
^ Adaptive oxygen sensor control.
^ Adaptive idle speed control.
^ Metal catalytic converter.
^ ONE sensor for speed and reference mark - TDC sensor eliminated.
^ DME relay on central electric board.
^ EKP 4 fuel pump.
^ 16 ohm fuel injectors.
^ Polyamide fuel pipes.
^ Electronically controlled tank venting.
^ Water-proof oxygen sensor.
^ One knock sensor for each bank of cylinders, on sensor bridges.

ADAPTIVE IDLE SPEED CO LEVEL
There is adaption of idle speed CO level in cars equipped with catalytic converter and correctly coded DME control unit. This compensates for environmental conditions (air pressure, etc.) and specific engine tolerances. Adaption of idle CO level eliminates adjustments on air flow sensor. Since a curve family displacement is stored in memory, engine must be run at operating temperature about 10 minutes after a possible break of battery (+) on DME control unit, to allow adaption to nominal values. Break is possible by disconnection of battery or unplugging control unit.


SELF DIAGNOSIS FUNCTION:
If the self diagnostic circuit ("on board diagnostics") in the ECU detects a fault in the ignition system, it will activate the "CHECK ENGINE" light. By extracting the fault codes from the diagnostic socket, you can determine what component or components need further testing or replacement.