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

NATIONAL LOW EMISSION VEHICLE PROGRAM

The concept of a "Low Emission Vehicle Program" was originally developed and implemented by the California Air Resource Board (CARB or ARB) in the late 1980s. This was necessary to address the unique air quality conditions in California. The LEV Program required that all new vehicles sold in California comply with ARB tailpipe emission standards and that vehicle manufacturers warranty emission control devices for longer periods of time ensuring higher air quality standards.

The California program established the criteria for each level of compliance and provided them with their now well known names; TLEV (Transitional Low Emission Vehicle), LEV (Low Emission Vehicle) and ULEV (Ultra Low Emission Vehicle).

With each level of compliance, the requirements become more stringent. Vehicles must comply with the set of values during cold engine start up as well as maintain expected levels through the life of the vehicle.

The EPA adopted the ARB program as the model for the National Low Emission Vehicle Program (NLEV).

The NLEV program has been used voluntarily by the northeastern states of the U.S. to address increasing smog problems in this area of the country.

NATIONAL LOW EMISSION VEHICLE PROGRAM COMPLIANCE SPECIFICATIONS

The NLEV program became law earlier this year. The law requires that all vehicles sold in the northeastern states of the country comply with the NLEV standards. Compliance level is based on the total number of vehicles sold starting with the 1999 model year. Complete national phase in will be realized by 2004.

The NLEV program will reduce air pollution nationwide, harmonize Federal and California standards to reduce manufacturers design and testing costs and to avoid a patchwork of statewide regulatory requirements. All of the recent advancements in emission control technologies are due to EPA compliance.

The evolution of the 1999 model year BMW engines described in this manual is partly due to achieving LEV compliance. However, there are changes that have been made to "technically update" the engines, helping to maintain the world class performance and reliability of our vehicles.

MANAGING VOLATILE ORGANIC COMPOUNDS

Volatile Organic Compounds (VOCs) are hydrocarbon-based emissions released through evaporation or combustion. Tailpipe emissions are not the only contributor of VOCs. The term "VOC" is usually used in regard to stationary emission sources which escape to atmosphere and contribute to poor air quality.

The most familiar VOC is fuel system hydrocarbons (gasoline vapors). However, other VOCs are produced by motor vehicles. These include evaporating engine oil, windshield washer fluid, paints, solvents and the gradual outgassing of petroleum based vehicle components such as plastics, rubber materials and compounds.

Identifying Volatile Organic Compounds (VOCs). Scheme 335

The EPA has addressed outgassing or release of VOCs to atmosphere by categorizing and mandating the following

1. Use vehicle components and materials manufactured to minimize VOCs. BMW only uses "environmentally friendly" products, components or materials which minimize VOC generation.
2. Running Losses Compliance: Reduce the generation of fuel system HC as the vehicle is being driven.
3. Monitor the vehicles evaporative fuel system for leaks (OBD II compliance).
4. Onboard Refueling Vapor Recovery (ORVR) Compliance: Reduce the release of fuel system HC to atmosphere while refueling.

The following pages provide an overview of the systems added to the vehicles to meet the EPA requirements. Attend the Engine Electronics (ST055) and On Board Diagnostics II (ST060) technical training courses for detailed functionality and hands-on diagnostic practical exercises for these systems.

RUNNING LOSSES

The fuel system is the largest contributor to running losses. For example

1. An electric fuel pump cycles the entire contents of the fuel tank through the fuel rail and back to the tank twice every hour.
2. The fuel absorbs the heat of the engine compartment as it continually cycles through the fuel rail and raises to a temperature as high as 158°F.
3. The added heat causes the gasoline to vaporize increasing the amount of HC in the fuel system.
4. If a leak develops in the system or when the fuel cap is removed at the gas station the additional gasoline vapors generated by the heat of the engine compartment only add to the escaped VOC.

Fuel Systems Before Running Loss Compliance. Scheme 336

Fuel Systems After Running Loss Compliance. Scheme 337

The EPA requires a method of minimizing Running Losses. The system must minimize the temperature build up of the fuel to reduce the generation of hydrocarbons as the vehicle is being driven.

3/2 Way Running Loss Valve

Starting with the 1995 model year, a redesigned fuel pressure regulator with by-pass solenoid known as the 3/2 Way Running Loss Valve was introduced on a small percentage of 325i models. As of the 1998 model year all BMW vehicles are now equipped with the valve.

The valve is located under the vehicle away from the engine compartment heat and incorporates the fuel pressure regulator. During engine start, the valve is activated providing 100% fuel flow to the fuel rail for 20 seconds. After 20 seconds, the valve is switched off providing an open port for fuel return back to the tank.

A regulated fuel supply is continually provided to the fuel injectors for combustion but the supply is not returned to the tank.

3/2 Way Running Loss Valve Operational System Diagram (Open). Scheme 338

The addition of the 3/2 Way Running Loss valve prevents the build up of heat in the return fuel flow reducing HC vapor generation in the fuel tank providing Running Loss Compliance.

3/2 Way Running Loss Valve Operational System Diagram (Close). Scheme 339

Evaporative System Monitoring

As part of OBD II compliance, the engine control module must monitor the evaporative fuel system for leaks as small as 1.0mm (.040").

E36 TLEV Vacuum System

Starting with the 96 328i and through the 97/99 model years on all E36 vehicles, the fuel tank and evaporative system was modified to comply with evaporative system leak detection and for monitoring purge valve function.

Components

The evaporative system was redesigned from previous systems. Additional components were added to provide leak detection capabilities and to store a larger volume of fuel hydrocarbons. The components include

Scheme 340

1. Charcoal Canister with integral Shut Off Valve
2. Liquid/Vapor Separator
3. Evaporative Purge Valve
4. Vehicle Fuel Tank
5. Fuel Tank Pressure Sensor (transducer) (Scheme 340): E36 TLEV Vacuum System Diagram

The Leak Diagnosis Pump (LDP) was added to the evaporative fuel system as a new component replacing the electric shut off valve on the charcoal canister and fuel system pressure sensor of the E36 TLEV vacuum system.

Leak Diagnosis Pump (LDP System) Diagram. Scheme 341

0.5 mm Leak Detection Compliance

0.5 mm leak detection compliance was originally scheduled for E46 and Z3 vehicles (excluding M) starting with 4-99 production. Compliance phase in has been postponed until model year 2000. Vehicle control modules were however produced to comply with the smaller 0.5mm diameter leak detection program prior to the postponement decision.

Therefore, E46 and Z3 vehicles with MS 42.0 engine management system (SOP 4-99) will detect evaporative system leaks as small as 0.5 mm and set a specific fault code. However the check engine light will not illuminate if this specific fault is determined.

This system will continue to monitor the evaporative system as it currently does and illuminate the check engine light following the existing OBD II criteria for 1.0mm leak detection.

On-Board Refueling Vapor Recovery (ORVR)

The ORVR system recovers and stores hydrocarbon fuel vapor that was previously released during refueling. Non ORVR vehicles vent fuel vapors from the tank venting line back to the filler neck and in many states reclaimed by a vacuum receiver (Stage II) on the filling station's fuel pump nozzle.

When refueling, the pressure of the fuel entering the tank forces the hydrocarbon vapors through the tank vent line to the liquid/vapor separator, through the rollover valve and into the charcoal canister.

The HC is stored in the charcoal canister, and the system can then "breathe" through the LDP and the air filter.

On-Board Refueling Vapor Recovery (ORVR) Flow Diagram. Scheme 342

ORVR phase in started in the 1998 model year. By model year 2000, all new vehicles sold must be equipped with an ORVR system. The EPA estimates an average of 78 million gallons of gasoline will have been saved from evaporation between the years 1998 and 2020. Additionally, 400,000 tons of smog producing volatile organic compounds (VOC) will be captured annually because of ORVR.

DME-ME 7.2 ENGINE MANAGEMENT SYSTEM

DME - ME 7.2 is the next generation of engine management systems for current and future powertrain control. ME 7.2 replaces M5.2.1 for all 8 cylinder engine applications. The "ME" designation identifies the system as M = Motronic, E = EML.

Scheme 343

Scheme 344

1. Manufactured by Bosch to BMW specifications
2. 134 pin SKE (standard shell construction) control module located in E box
3. New diagnostic communication protocol (KWP2000)
4. Uses break-out box set (P/N 90 88 6 121 300)
5. Integral EML throttle control system monitors an interior installed PWG actuates an electric throttle valve (EDK) (Scheme 343): Identifying ME 7.2 Location In E-Box
6. Integral Cruise control functionality monitors cruise control requests monitors brake pedal and clutch switches carries out throttle control directly via EDK
7. Carries out DSC III torque reduction requests.
8. VANOS control
9. Integrated altitude sensor
10. Integrated temp sensor for monitoring E box temperatures
11. Control of E-box fan
12. One touch engine start control
13. Oxygen Sensor heating
14. Engine overrev & Max speed limitation
15. Active Hall sensor for camshaft position monitoring
16. Single speed secondary air injection system
17. Electrically heated coolant system thermostat (same function as previous M62 engine)
18. Longlife spark plugs
19. IHKA Auxiliary Fan control (Scheme 344): Identifying ME 7.2 Control Unit Connectors

This training manual only covers new or modified input signal components and output control functions. The balance of the ME 7.2 system functions are as per previous engine management systems. Refer to ENGINE ELECTRONICS and OBD II training course material for detailed functional descriptions.

ME 7.2 Operation Diagram. Scheme 345

Camshaft Position Sensors

Located on the upper timing case covers, the camshaft position sensors monitor the position of the camshafts to establish start of ignition firing order, set up sequential fuel injection triggering and for accurate camshaft advance-retard (VANOS) timing feedback.

Each intake camshaft's advance-retard angles are adjusted simultaneously yet independently. For this reason ME 7.2 requires a camshaft position sensor on each cylinder bank for accurate feedback to monitor the VANOS controlled camshaft positioning.

The sensors are provided with operating power from the ECM main relay. The sensors produce a unique asymmetrical square-wave signal representative of the impulse wheel shape. The sensors are new in the fact that they are "active" hall effect sensors. Active hall sensors provide

1. Low signal when a tooth of the camshaft impulse wheel is located in front of the sensor.
2. High signal when an air gap is present.

The active hall sensors supply a signal representative of camshaft position even before the engine is running. The ME 7.2 determines an approximate location of the camshafts positions prior to engine start up optimizing cold start injection (reduced emissions.)

Camshaft Position Sensor System Diagram. Scheme 346

Hot Film Air Mass Sensor (HFM 5)

The M62 TU is equipped with a new Hot Film Air Mass Sensor identified as HFM 5. It is a combined air mass/intake air temperature sensor. The separate intake air temperature sensor is no longer used on the M62 TU.

Locating Hot Film Air Mass Sensor (HFM 5). Scheme 347

Hot Film Air Mass Sensor (HFM 5) System Circuit Diagram. Scheme 348

The HFM 5 is provided with operating power from the ECM main relay. Based on calculated intake air mass, the HFM 5 generates a varying voltage between 0.5 and 4.5 volts as an input signal to the ME 7.2 An additional improvement of the HFM 5 is that the hot film element is not openly suspended in the center bore of the sensor as with previous HFMs. It is shrouded by a round fronted plastic labyrinth which isolates it from intake air charge pulsations.

This feature allows the HFM to monitor and calculate the intake air volume with more accuracy. This feature adds further correction for calculating fuel injection "on" time (ti) which reduces emissions further.

Cut-Away View Of HFM 5. Scheme 349

Integrated Ambient Barometric Pressure Sensor

The ME 7.2 Control Module contains an integral ambient barometric pressure sensor. The sensor is part of the SKE and is not serviceable. The internal sensor is supplied with 5 volts. In return it provides a linear voltage of approx. 2.4 to 4.5 volts representative of barometric pressure (altitude).

The ME 7.2 monitors barometric pressure for the following reasons

Scheme 350

1. The barometric pressure signal along with calculated air mass provides an additional correction factor to further refine injection "on" time.
2. Provides a base value to calculate the air mass being injected into the exhaust system by the secondary air injection system. This correction factor alters the secondary air injection "on" time, optimizing the necessary air flow into the exhaust system.
3. To recognize downhill driving to postpone start of evaporative emission leakage diagnosis. (Scheme 350): Integrated Barometric Pressure Sensor System Diagram

Radiator Outlet Temp Sensor

First seen on the MS 42.0 control system, the ME 7.2 uses an additional water temperature sensor located on the radiator outlet.

ME 7.2 requires this signal to monitor the water temperature leaving the radiator for precise activation of the IHKA auxiliary fan.

Radiator Outlet Temp Sensor & Circuit Diagram. Scheme 351

DSC III Road Speed Signal

ME 7.2 receives the road speed signal directly from the DSC III control module for maximum vehicle speed management. The DSC control module provides a processed output of the right rear wheel speed sensor as a digital square wave signal. The frequency of the signal is proportional to the speed of the vehicle (48 pulses per one revolution of the wheel).

The cruise control function (FGR) of the ME 7.2 also monitors vehicle speed from the redundant vehicle speed CAN bus signal. The CAN bus speed signal is provided by the DSC III control module and based on the combined average of both front wheel speed signals.

Additionally, ME 7.2 monitors all four wheel speed signals via CAN bus signalling to detect abrupt fluctuations in vehicle speed signals for the purpose of detecting rough road surfaces. This is continuously monitored as part of the OBD II emission requirements providing a correction factor for misfire detection plausibility. Earlier systems only monitored the right rear speed signal input from DSC.

DSC III - Road Speed Signal System Diagram. Scheme 352

Accelerator Pedal Sensor (PWG)

The driver's application of the accelerator pedal is monitored by a PWG sensor in the driver's footwell as with previous non-bowden cable EML systems.

The PWG provides two separate variable voltage signals to the ME 7.2 control module for determining the request for operating the Electric Throttle Valve (EDK) as well as providing a kickdown request with automatic transmission vehicles.

The ME 7.2 monitors the changing signal ranges of both circuits as the pedal is pressed from LL to VL.

PWG Pot 1 = 0.5V to 4.5 V

PWG Pot 2 = 0.5V to 2.0 V

Standard transmission vehicles (E39 540i) have slightly lower voltage signals at max throttle position due to the throttle pedal stop (ie Pot 1 = 3.8volts).

Accelerator Pedal Sensor (PWG) System Circuit Diagram. Scheme 353

However, ME 7.2 programming recognizes the lower values of a standard transmission vehicle as the max throttle position.

In vehicles equipped with an automatic transmission (A5S 440Z), the ME 7.2 recognizes the max pedal value (4.5V) as a kickdown request and signals the AGS via CAN bus.

The signals are continually monitored for plausibility. If the signal ranges are detected as incorrect, ME 7.2 will only utilize the signal of lesser voltage value as a failsafe measure. With this condition, the EDK will also be set to idle (LL) whenever the brake pedal is pressed. Refer to PWG MONITORING AND FAILSAFE OPERATION .

PWG - Signal Voltage Graph. Scheme 354

EDK Throttle Position Feedback Signals

The EDK throttle plate position is monitored by two integrated potentiometers. The potentiometers provide DC voltage feedback signals as input to the ME 7.2 for throttle and idle control functions.

Feedback potentiometer 1 provides a signal ranging from 0.5V (LL) to 4.5V (VL)

Feedback potentiometer 2 simultaneously provides a signal ranging from 4.5V (LL) to 0.5V (VL).

EDK Throttle Position System Circuit Diagram. Scheme 355

Pot signal 1 is the primary signal, signal 2 is used as a plausibility cross-check through the total range of throttle plate movement.

If there is an open or short in signal 1, signal 2 is used as a temporary substitute providing failsafe operation (faults stored).

If the signals are not plausible, ME 7.2 determines intake air mass from the HFM signal (virtual Pot 3) and compares it with Pot 1 and Pot 2. The signal that is closest to virtual Pot 3 is then used and the other disregarded.

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).

Refer to EDK MONITORING AND FAILSAFE OPERATION .

Throttle Plate Position - Signal Voltage Graph. Scheme 356

MFL Cruise Control Data Signal

The ME 7.2 control module provides the FGR cruise control function. Throttle activation is provided by ME 7.2 automatic control of the EDK and monitoring of the throttle plate position feedback potentiometer signals.

All of the familiar driver requested cruise control function requests are provided to the ME 7.2 control module via the MFL control module on a single FGR data signal wire.

MFL Cruise Control System Circuit Diagram. Scheme 357

Brake Light Switch

The Electronic Brake Switch (Hall effect) provides brake pedal position status to the ME 7.2. The control module monitors both the brake light and a separate brake light test switch circuits for plausibility.

When the brake pedal is pressed the brake light segment of the switch provides a ground signal. Simultaneously, the brake light test switch (located in the same housing) provides a high signal.

Clutch Switch

The clutch switch is equipped on manual transmission vehicles for deactivating the FGR. It is housed in the footwell by the clutch pedal. The hall effect clutch switch interrupts the single wire circuit to the ME 7.2 control module when the clutch pedal is pressed.

ME 7.2 & M5.2.1 CAN BUS TOPOLOGY

The CAN bus consists entirely of a twisted pair wire set. This configuration eliminates the need for a ground shield.

The Engine Control Modules (ME7.2 & M5.2.1) have two CAN bus communication ports, one dedicated to AGS (and DME I of the 750iL to EML) and the other for the balance of the vehicle's CAN bus control modules.

This configuration improves the reliability of CAN bus signalling. If an open occurs in one area, the other control systems can still communicate on either side of the open.

However, signals not reaching their intended recipients will cause CAN bus faults to be stored in the affected systems.

ME 7.2 & M5.2.1 CAN BUS Topology System Diagram. Scheme 358

ME 7.2 CAN BUS System Diagram. Scheme 359

Fuel Pump Relay Control

ME 7.2 controls the fuel pump relay as with previous systems with regard to engine speed input for continual activation of the relay.

When MRS III is incorporated into production vehicles (SOP 3-99) the ME 7.2 will also switch off the fuel pump relay when an airbag is activated as an additional safety function.

Fuel Pump Relay Control System Diagram. Scheme 360

E-Box Fan Control

The E Box fan is controlled by ME 7.2. The control module contains an integral NTC temperature sensor for the purpose of monitoring the E box temperature and activating the fan.

When the temperature in the E-Box exceeds predetermined values, ME 7.2 provides a switched ground for the E Box fan to cool the E box located control modules.

With every engine start-up, ME 7.2 briefly activates the fan ensuring continued fan motor operation for the service life of the vehicle. This feature is intended to prevent fan motor "lock up" from lack of use due to pitting or corrosion over time.

E-Box Fan Control System Diagram. Scheme 361

Secondary Air Injection

The secondary air injection system is new to the 4.4 liter V8 engine. The system consists of the same components as previous systems with V8 specific locations.

Identifying Secondary Air Injection System Components (1 Of 2). Scheme 362

Identifying Secondary Air Injection System Components (2 Of 2). Scheme 363

The DME ME7.2 control unit controls the vacuum vent valve and the secondary air injection pump relay separately but simultaneously.

The secondary air pump operates at a start temperature of between 10°C and 40°C. It continues to operate for a max. of 2 minutes at idle speed.

ME 7.2 contributes an additional correction factor for secondary air "on" time with the additional input from the integral ambient barometric pressure sensor.

This sensor provides a base value to calculate the air mass being injected into the exhaust system. This helps to "fine tune" the secondary air injection "on" time, optimizing the necessary air flow into the exhaust system which reduces the time to catalytic converter light-off.

DME ME7.2 Control Unit System Diagram. Scheme 364

Auxiliary Fan Control

The Auxiliary Fan motor incorporates an output final stage that activates the fan motor at variable speeds.

The auxiliary fan is controlled by ME 7.2. The motor output stage receives power and ground and activates the motor based on a PWM signal (10 - 100 Hz) received from the ME 7.2.

Similar to the aux fan in the E46 with MS 42.0 control, the fan is activated based on the following factors

Identifying Auxiliary Fan Control & Control Module. Scheme 365

1. Radiator outlet temperature sensor input exceeds a preset temperature.
2. IHKA signalling via the K and CAN bus based on calculated refrigerant pressures.
3. Vehicle speed
4. Battery voltage level

When the over temperature light in the instrument cluster is on (120°C) the fan is run in the overrun function. This signal is provided to the DME via the CAN bus. When this occurs the fan is run at a frequency of 10 Hz.

Auxiliary Fan Control System Diagram. Scheme 366

Electric Throttle Valve (EDK) Control

The throttle valve assembly of the M62 TU is an electric throttle valve (EDK) controlled by an integral EML function of the ME 7.2. The throttle plate is positioned by a gear reduction DC motor drive.

Similar to the original Bosch EML 1.2 and 1.7 systems, the motor is controlled by proportionately switched high/low PWM signals providing precise plate positioning. The PWM signal is at a basic frequency of 2000 Hz.

Electric Throttle Valve (EDK) Control System Diagram. Scheme 367