Engine Performance Dme 7.2 - Overview: Overview BMW 7 series E38 facelift

Functional Overview

The ECM detects leaks by closing the shut off valve on the charcoal canister to seal the system. The purge valve is opened subjecting the evaporative system and fuel tank to manifold vacuum. The ECM measures the vacuum value with the fuel tank pressure sensor. The duration of time the system retains the vacuum is the method used to determine the system's integrity.

1. The function of the LDP is to pressurize the fuel tank and the evaporative emission system to detect leaks. The pump also serves as the fresh air inlet path during normal purge operation when leak diagnosis is not occurring.
2. The pump contains a spring loaded diaphragm which is moved up and down by solenoid controlled engine vacuum to generate the air pressure used for leak testing.

LDP System Functional Overview. Scheme 329

Scheme 330

Scheme 331

1. During a leak test, the normally open vent valve is sprung closed to retain the built up pressure.
2. The purge valve(s) are also sprung closed to seal the system.
3. The reciprocation of the diaphragm pulls in filtered ambient air and pumps it into the fuel system via the purge canister as the vacuum supply is repetitively opened and closed electrically by the ECM. (Scheme 330): LDP System (Closed Position)
4. The ECM monitors the diaphragm movement through a reed contact feedback signal and compares it to its activation output frequency of the vacuum solenoid in the LDP.
5. As the pump continues to operate the diaphragm begins to slow down against the built up pressure in the system. The time delay between the vacuum solenoid activation and the reed contact feedback is the basis for leak detection. (Scheme 331): LDP System (Leak Detection Position) If the reed contact feedback signal slows down considerably this indicates the pressure is being held by the system and no leaks are present. If the reed contact feedback signal is slowed down but not to the satisfaction of a sealed system the ECM will determine a small leak is present. If there is no delay in the feedback signal the ECM determines a large leak is present (ie: missing fuel filler cap).

Functional Description

When the accelerator pedal is moved, the PWG provides a change in the monitored signals. The ME 7.2 compares the input signal to a programmed map and appropriately activates the EDK motor via proportionally high/low switching circuits. The control module self checks it's activation of the EDK motor via the EDK feedback potentiometers.

Integral Electric Throttle System (EML) Diagram. Scheme 332

Requirements placed on the Electric Throttle System

1. Regulate the calculated intake air load based on PWG input signals and programmed mapping.
2. Control idle air when LL detected with regard to roadspeed as per previous systems.
3. Monitor the driver's input request for cruise control operation.
4. Automatically position the EDK for accurate cruise control (FGR) operation.
5. Perform all DSC III throttle control interventions.
6. Monitor and carryout max engine and roadspeed cutout.

PWG Signal Monitoring & PWG Failsafe Operation

1. As a redundant safety feature the PWG provides two separate signals from two integral potentiometers (Pot 1 and Pot 2) representing the driver's request for throttle activation.
2. If the monitored PWG potentiometer signals are not plausible, ME 7.2 will only use the lower of the two signals as the driver's pedal request input providing failsafe operation. Throttle response will be slower and maximum throttle position will be reduced.
3. When in PWG failsafe operation, ME 7.2 sets the EDK throttle plate and injection time to idle (LL) whenever the brake pedal is depressed.
4. When the system is in PWG failsafe operation, the instrument cluster matrix display will post "Engine Emergency Program" and PWG specific fault(s) will be stored in memory. Refer to «ACCELERATOR PEDAL SENSOR (PWG)»(ref-224196-S12771854572006030800000) for additional PWG component and signal information.

EDK Feedback Signal Monitoring & EDK Failsafe Operation

1. The EDK provides two separate signals from two integral potentiometers (Pot 1 and Pot 2) representing the exact position of the throttle plate.
2. EDK Pot 1 provides the primary throttle plate position feedback. As a redundant safety feature, Pot 2 is continuously cross checked with Pot 1 for signal plausibility.
3. If plausibility errors are detected between Pot 1 and Pot 2, ME 7.2 will calculate the inducted engine air mass (from HFM signal) and only utilize the potentiometer signal that closely matches the detected intake air mass. The ME 7.2 uses the air mass signalling as a "virtual potentiometer" (pot 3) for a comparative source to provide failsafe operation. If ME 7.2 cannot calculate a plausible conclusion from the monitored pots (1 or 2 and virtual 3) the EDK motor is switched off and fuel injection cut out is activated (no failsafe operation possible).
4. The EDK is continuously monitored during all phases of engine operation. It is also briefly activated when KL 15 is initially switched on as a "pre-flight check" to verify it's mechanical integrity (no binding, appropriate return spring tension, etc). This is accomplished by monitoring both the motor control amperage and the reaction speed of the EDK feedback potentiometers. If faults are detected the EDK motor is switched off and fuel injection cut off is activated (no failsafe operation possible). The engine does however continue to run extremely rough at idle speed.
5. When a replacement EDK is installed, the ME 7.2 adapts to the new component (required amperage draw for motor control, feedback pot tolerance differences, etc). This occurs immediately after the next cycle of KL 15 for approximately 30 seconds. During this period of adaptation, the maximum opening of the throttle plate is 25%.

Refer to EDK THROTTLE POSITION FEEDBACK SIGNALS for additional EDK feedback signal information.