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Replacing a potentiometer with something to lock in 1 value

Discussion in 'General Electronics' started by hotrod, May 16, 2005.

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  1. hotrod

    hotrod Guest

    Hello, I am trying to clean up the engine bay of my Mustang. It is
    drag car and I no longer need emissions equipment.

    I want to remove what is called the EGR system. Exhaust Ga

    This consists of a solenoid which controls vacuum to a EVP Exhaus
    Valve Position Sensor

    It is a potentiometer I believe. It is a plunger that moves in and ou
    when vacuum is applied/removed. I have completely removed the vacuu
    to it and it always read closed, giving me a check engine light. Yo
    can trick it by wiring a gizmo to the connector to make the EEC (ca
    computer) always things it is open and getting a signal

    There are 3 wires
    1)VREF (voltage referecne from computer) This is 5.0volt
    2)Signal Return (ground to computer
    3)Signal Voltage to computer

    As vacuum is applied to the vavle, the plunger moves and sends a lowe
    voltage (from 5.0volts) to the computer

    The test for the sensor is 5500 ohms fully closed, to 100 ohms full

    I do not know how to wire the 3 wires or what to use for parts to mak
    a permanent, say 2500 ohms signal to the computer. I understand tha
    the sensor is supplied 5.0 volts and the potentiometer (?). Whe
    there is no vacuum present, the computer sees very little voltage
    and as vacuum is applied, the plunger moves and drops resistance
    allowing more voltage to be read by the computer

    I know there is a simple way to wire up the sensor to put it at
    constant 2500 ohms or so, but I do not know what to use. Would I us
    a transistor, multiple resistors

    I can fool the computer by locking down the plunger to read hal
    closed, but I want to removed the sensor altogether and replace i
    with a simple resistor type settup that I can connect directly to th
    wires inside the car near the computer

    Thanks for any help. I do know some electronics, but it is limited t
    fairly simple circuits. I'm not really a beginner, but don't have an
    formal training or schooling

  2. DesignGuy

    DesignGuy Guest

    The potentiometer is a resistor (two outside connections) with a sliding tap
    (middle connection). As the pot is turned the resistance between one end and
    the tap increases, while the resistance between the opposite and and the tap

    What you need to do is set the pot where you need it to be, and then remove
    the wires (carefully noting their original locations). The using a
    multimeter measure the resistance between one end and the center tap, and
    then the other end and the center tap. Those are the values of the two
    resistors (R1 and R2) that you will need.

    The circuit will look like this:


    The vertical lines indicate where the wires will connect. One end of each of
    the two resistors will be connected to each other.
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