Vems PnP UrS4/S6 Installation Instructions

VEMS PnP UrS4/UrS6 ECU Installation Instructions


Package Contents:

  • ECU 

  • flying lead wideband harness

  •    LSU wideband connector + pins/seals
  • 6-pin aux output connector with pins/seals

  • 2-pin idle 'diode' adapter







Before plugging in your new VEMS ECU, follow these important steps:
Swap two pins on the “Crank Home” harness
Run Wideband harness and terminate pins
Connect idle diode adapter
Verify settings via vemstune

Swapping the “Crank Home” pins:

    Inside the engine bay underneath the black plastic power output stage cover you'll find a row of electrical plugs.  Locate the 3 pin black female connector that leads to a black 3 pin male connector that goes to one of the VR sensors attached to the bell housing on the transmission.  This is the sensor that reads the pin on the flywheel, and two of the pins on the car harness need to be swapped.  Note:  If you purchased our optional 3 pin adapter, you can simply plug it inline between the vehicle harness and the VR sensor, the cable internally accomplishes the pin swap without removing any pins.  Otherwise, pull back the rubber boot on the connector and eject the purple 'cartridge' that holds the pins by releasing the plastic tab on the connector (see photo):



After removing the purple pin cartridge, swap the red and violet wires.  Ejecting the pins can be tricky, the easiest way is to insert a thin piece of wire (like mig welding wire) into the slot above and below the pin to release the tabs, and then pull back gently on the wire to remove the pin.

    After the pins are swapped, the red wire should be at position #2 (middle of the connector) and the purple wire should be at position #1
    Slide the pin cartridge back into the plug and push the rubber boot back into place.  If done correctly the factory ECU should still function just fine.  The purpose of this pin swap is to reduce the noise that is received by the ecu on this harness by swapping the shield and signal(-) wires.

    2)  Run Wideband Harness and Terminate Pins:

    The 5 pin and 6 pin connectors are supplied unconnected to make it easier to pass through the firewall of your car.  There is a rubber grommet on the passenger side of the car where the factory wiring harness comes through the vehicle.  Using a coat hanger, push one end through the grommet until you can grab the other end from the engine bay.  Inside the car wrap/tape the wires to the coat hanger and “fish” them through the firewall.  The female pins go toward the engine bay side, the male pins to the interior.  Tape the male pins to the fish from the engine bay side so that they will not deflect/bend when pulling them through the firewall, then pull the fish through from the interior side and terminate the connectors as described below.
    With the harness passed through the firewall the wires should be terminated in the LSU wideband connector as follows (there is a small piece of paper in with the harness that describes the routing as well).  Starting with the engine bay side of the harness (the oval wideband connector):

        Black->Pin 1
        Thick Red->Pin 3
        Thick Brown->Pin 4
        Blue->Pin 5
        Thin Red->Pin 6

    Note that pin 2 has no connection.  With all of the pins pushed into place on the wideband connector, push in the tab on the side of the connector to lock the pins in place.

    On the interior side of the harness, terminate the supplied 5 pin flat connector housing as follows:

        Black->Pin 1
        Thick Red->Pin 2
        Thick Brown->Pin 3
        Blue->Pin 4
        Thin Red->Pin 5

        When finished, just plug the LSU connector into a wideband sensor and plug the 5 pin flat connector into the VEMS ECU.  Note that a wideband sensor is not required for proper operation of the ECU.

    At this stage you are ready to plug the ECU into the factory wiring harness.  Remember to hook up the vacuum hose!

    3)  Connect Idle diode adapter
    unplug the idle stabilizer valve under the hood and connect the small 2-pin adapter supplied with your ecu in between the car wiring harness and the idle valve.  The purpose of this adapter is to prevent “flyback” voltage from hindering the actuation of the valve.

    4)  Install Vemstune and verify settings

    Install the latest available VemsTune .exe from the following URL:  Click on the 'Latest Stable' button.

    VEMS requires a serial connection to your computer to communicate.  If your computer does not have a serial port, a usb to serial converter may be used.  Adapters are available through as well.  Make sure your serial cable is a 'straight through' style cable and not a 'null modem' cable. 
    With your ECU connected to the computer and the key in the 'on' position, start the vemstune software.  If a dialog box does not appear asking you to enter a name for your ecu, you will first need to configure the serial port.  To do this, click on preferences->ecu communication.  Then click on the 'detect' button.  The software will scan through your serial ports until if finds the one connected to the ecu.  On success it will report “ecu detected”.  Closing the window you should see a number of gauges showing you the readings from the various sensors connected to the computer.
    Now you can attempt to start the car.  Every ECU shipped is supplied with a basemap that should start the car with no changes, however if larger or smaller injectors are used this could cause the car to run poorly or not start.  The main fuel injector sizing in vemstune is controlled via the 'req fuel' parameter under Base Setup->Engine Setup.  Larger req_fuel numbers will inject more fuel under all conditions (for smaller injectors), and smaller numbers will inject less fuel (for bigger injectors).  As a guideline, set req_fuel according to the following calculation:  req_fuel = 6.49 * (D / N / I)   where D= engine displacement (ccs), N = number of fuel injectors, and I = injector flow rate (cc/min).  To allow for finer grain fuel control I usually use 75% of this calculated number.  So for an urS4 with stock injectors (280 cc/min @3 bar), req_fuel = 6.49 * (2200 / 5 / 280) = 10.2 * .75 = 7.65.
    The actual req_fuel used will vary, depending on the entries made in the VE table.
Use the wideband to determine if more or less fuel is necessary.  1.0 lambda corresponds to all the green dots on the main display being illuminated but none of the red dots.

Wideband Sensor Calibration
    If you ordered your ecu with a wideband sensor this step has probably already been done for you.  To calibrate your own wideband sensor to the VEMS, disconnect the sensor from the exhaust pipe (it must sample free air to be properly calibrated).  From within the vemstune menu with the ignition on, go to tools->calibrate wideband o2.  Click on the "Start Cal" button.  wait about 30-45 seconds for the numbers to start to read.  your target value is 20.9 (which corresponds to the percentage of oxygen in atmospheric air everywhere on earth).  If your numbers are reading LOWER than 20.9, enter a HIGHER value in the calibration constant field, and click "send".  the number should jump higher.  Once you have the numbers as close to 20.9 as possible, click the "burn" button, "Stop Cal".  Wait for the numbers to steady out to 0 then repeat the process again (clicking on "Start Cal") to validate that 20.9 is attained.  When done, click "stop cal" and close the window.

    For both fuel and ignition timing tuning, the VEMS datalog is a valuable tool.  To create a data log, click on the “log” button in the uppper right of vemstune.  Clicking the button again will stop the current log and start a new one.  Files by default are saved in the my documents -> VEMS_FILES->ecu_serial_number directory.  To view the log, select file->open log file.  The slider bar in the upper section of the page can be used to scroll through time in the log.  You can also convert your log to a csv file via the tools->vemslog to csv utility. 

Fuel Tuning
    Once your main req_fuel parameter is adjusted, fuel delivery can be adjusted via the VE table (Tuning->RPM/MAP Fuel VE).  The table is mapped for rpm vs boost.  The larger the numbers, the more fuel to be injected at that load cell.  Watch the feedback from the wideband sensor in the datalog to help you determine what direction to go.  Tune for around .8 lambda under full load, 1.0 lambda at idle, and 1.1 lambda on light cruise.

Ignition Timing Tuning
    The timing table is available under the Tuning->RPM/MAP Ignition.  Just like the VE table, the map is rpm vs boost.  The numbers are in degrees.  Typically the spark curve on a turbo engine will ramp up from low to high rpm with a 'dip' in timing at the torque peak which will be located where boost first hits peak.  On a stock turbo this is typically around 3000 rpm, larger turbos will peak later. 

Additional Information:
    Store website:
    VEMS homepage: (check the wiki for lots of great user-contributed information)


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