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  1. #1
    LTX Regular


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    May 2019
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    DARREN BRANDON
    Vehicle
    1983 jaguar xj6
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    Default Sensor ground vs regular ground

    Hopefully this is just a yes / no answer ( for the first part anyways )from someone that knows more than i do!
    whilst redoing my rear gears is on hold while I look for another rear, I figured I would work on getting ac working through the pcm versus the jag controls because not only do using jag controls not have any useable
    pressure sensors installed, but initiall turn of of ac with drop idle enough to stall car until iac can catch up.
    I have had to redo a few wires that were cut out of harness before I bought it, and am down to final few.... One of last items is hooking up the pressure sensor on high side line by drier, One of those wires is 5 v. Reference, another is sensor input, and third connects to sensor ground, can I simply use a
    regular ground? Or will that screw me up?? If I cannot, where’s another spot to pick up that sensor ground??

    thanks in advance

    Darren
    oh, it a 94 lt1 complete drivetrain swapped into 83 jag xj6

  2. #2

    Default

    Sensor ground is not the same as chassis ground.

    Best way, find a spare pin at the PCM for sensor 5v ground and pin it there. Other way would be to find a good known sensor ground line and tap in.
    Correlation does not imply causation.

    Una salus victis nullam sperare salutem

  3. #3
    LTx Guru


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    Apr 2013
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    1994 Formula
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    Default

    Use the factory wiring diagram. The A/C Pressure sensor has a grey wire that supplies 5 volts (regulated) reference from pin B29. That pin also feeds the MAP sensor, and A/C EVAP Temp sensor. Similarly the ground (also called low reference) from pin B16 supports the A/C Pressure sensor, MAP sensor, IAT sensor, and A/C EVAP Temp sensor.

    The purpose of having the PCM provide both the high reference (5.0 volt) and low reference (ground potential) is to insure the reference voltage is held as close as possible to 5.0 volts. The PCM has the circuitry to maintain that voltage.

    If you use a random chassis ground there can be variability in the quality of the ground that affects the accuracy (+/-) of the 5 volt reference, thereby throwing off the accuracy of the sensor output signal. The PCM is converting the signal voltage to degrees, psi, etc..

  4. The Following 2 Users Say Thank You to Injuneer For This Post:


  5. #4
    LTX Regular


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    DARREN BRANDON
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    1983 jaguar xj6
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    Default

    Got it, thank you Fred!

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