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Test Group 1BMXV05.4LEV

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  1. Evaporative System Leak Measurement -  Evaporative system monitoring permits detection of leaks in evaporative system with a diameter of .039" (1.0 mm) and greater. Using a Leak Detection Pump (LDP), a vacuum actuated pump located at the atmospheric connection of the evaporative canister, a pressure test of the evaporative system is performed in the following order:
    • During the fast pulse phase the evaporative system is set under a defined pressure. The pressure in the evaporative system after the fast pulse phase may be higher or lower than the defined pressure depending on fuel level in tank.
    • Natural frequency phase that follows past pulse phase is therefore needed to adjust pressure to its correct value.
    • During final measurement phase, time between pump strokes of LDP is evaluated. In case of a time between pump strokes below a preset threshold, a leak is assumed to be present. During pressure test, purge valve needs to be shut. After test canister purge is resumed, remaining pressure in evaporative system is bled off. To have maximum capacity (or minimal loss of purge air due to leak detection) test normally runs after engine cold start. However, under certain circumstances, test may be preliminary aborted and started again later during engine run if all conditions for restart of test are met.
  2. Monitoring Structures Of Leak Measurement (LDP) Cold Start Conditions -  At time of engine start, value of intake air temperature monitor (TAL REF monitor) is initialized to maximum possible value. If a specified load and a specified vehicle speed is exceeded over a specific time, value of TAL REF is updated with value provided by intake air temperature sensor. This is only done if intake air temperature value is lower than value that is already represented by TAL REF. Therefore, TAL REF always represents minimum value of intake air temperature sensor found during conditions mentioned above. Using this technique, following sequences are possible:
    • Cold Start Conditions - Monitoring Structure -  See Fig 1.
    • Cold Start Conditions - Use Of Ambient Temperature Signal Provided By Vehicle Can Bus -  Leak measurement (LDP) component is specified for defined temperature range. To prevent component from being operated under unspecified conditions, ambient temperature is used as a condition for starting monitoring sequence after cold start. Ambient temperature signal is checked for circuit continuity later in driving cycle by means of intake air temperature monitor (TAL REF monitor).
      1. At time of engine start, value of intake air temperature monitor (TAL REF monitor) is initialized to maximum possible value.
      2. If a specified load and a specified vehicle speed is exceeded over a specific time, value of TAL REF is updated with value provided by intake air temperature sensor. This is only done if intake air temperature value is lower than value that is already represented by TAL REF. Therefore, TAL REF always represents minimum value of intake air temperature sensor found during conditions mentioned above.
        Fig 1: Monitoring Structure Of Leak Measurement (LDP)
        G00232347Courtesy of BMW OF NORTH AMERICA, INC.
    • Using this technique, following sequences are possible:
      1. Ambient temperature is within specified range and no leak is detected during monitor sequence: in this case system is considered to be without a leak and no fault code is stored.
      2. Ambient temperature is within specified range and a leak is detected during monitoring sequence: After conditions for updating intake air temperature monitor (TAL REF monitor) are met and TAL REF is within specified range, a fault code is stored. In case TAL REF is out of specified range no fault code is stored.
      3. Ambient temperature is out of specified range at time of engine start. This leads to a preliminary cancellation of monitoring sequence. Monitoring sequence is carried out as soon as all conditions for repetition are met after a preliminary cancellation.
  3. Condition For Preliminary Abort - Monitoring Structure -  See Fig 2.
    Fig 2: Monitoring Structure Condition For Preliminary Abort
    G00232348Courtesy of BMW OF NORTH AMERICA, INC.
  4. Condition For Preliminary Abort - Downhill Run Detection  LDP measures difference between the internal tank pressure and ambient pressure. In case of a vehicle moving downhill, internal tank pressure remains constant whereas ambient pressure increases. Consequently, pressure difference measured by LDP decreases which may cause detection of a leak that is not present (i.e. a false alarm). To prevent this, a downhill run detection that compares engine torque with a torque that is needed for driving the car on level terrain at a given speed, is implemented. Once a downhill run is detected, monitoring sequence is preliminary aborted. See Fig 3-Fig 6 .
    Fig 3: Condition For Repetition After Preliminary Abort
    G00232349Courtesy of BMW OF NORTH AMERICA, INC.
    Fig 4: Condition For Final Abort Of Monitoring Sequence
    G00232350Courtesy of BMW OF NORTH AMERICA, INC.
    Fig 5: Basic Monitoring Sequence
    G00232351Courtesy of BMW OF NORTH AMERICA, INC.
    Fig 6: Typical Pressure Over Time
    G00232352Courtesy of BMW OF NORTH AMERICA, INC.
  5. Evaporative Purge System Flow Check -  Purge flow from charcoal canister through purge valve is monitored after fuel system adaptation is completed and lambda controller is at closed loop condition. Diagnosis is started during regular purging.
  6. Monitoring Structure Of Evaporative Purge System Flow Check -  See Fig 7.
    • Step 1 - For Rich Or Lean Mixture -  Flow through purge valve is assumed as soon as lambda controller is compensating for a rich or a lean shift. After this procedure, diagnosis is completed and evaporative purge system resumes working normally.
      Fig 7: Monitoring Structure Of Evaporative Purge System Flow Check
      G00232353Courtesy of BMW OF NORTH AMERICA, INC.
  7. Step 2 - For A Stoichiometric Mixture -  In this case, lambda controller does not need to compensate for a deviation. Therefore, after finishing regular purging, purge valve is opened and closed abruptly several times. Effect of additional cylinder charge triggers a variation of engine idle speed. A predetermined value is reached if system functions properly and diagnosis procedure is completed. To start diagnosis function, several conditions have to be satisfied:
    • Vehicle speed = 0.
    • Engine at idle speed.
    • Closed loop of lambda controller.
    • Coolant temperature greater than fixed limit.
    • Transmission in gear.

    In addition, if diagnosis has already been started and one of the conditions has not been satisfied continuously, process will be interrupted and started again later. See Fig 8.

    Fig 8: Evaporative System Schematic
    G00232354Courtesy of BMW OF NORTH AMERICA, INC.
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