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Thread: Oil pressure sensor - incorrect readings

  1. #1
    Join Date
    Sep 2015
    Location
    In the shed or 1000km from home
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    Oil pressure sensor - incorrect readings

    Hey folks,
    I have an oil pressure sensor and gauge that i am plumbing up to my 300TDi.

    I have ran a wire to the gauge inside the cab yet the gauge is reading too low an oil pressure (11PSI!) than what the engine actually has (tested at about 40PSI-60PSI recently).
    If i move the gauge to a shorter length of wire (approx 50cm) the gauge reads more like what i would expect.

    I am presuming that the resistance of the length of wire is causing incorrect resistance readings from the sensor?
    I am not sure what to do about it though. The gauge of wire from the sensor looks pretty good to me - and is actually thicker than i wanted to use but it was all i had left in the shed. I can't really make the wire much thicker?

    Has anyone else had this problem? The gauge did not come with a pre-wired loom (that it could have been calibrated to).
    It is just some random branded gauge and sensor that i have used in the past to check oil pressure after rebuilds (connected with a really short bit of wire to the sensor).

    Any thoughts? Thanks!
    97 Disco 300Tdi, front & rear diff locked, hybrid turbo, full width intercooler, cranked front & rear arms,
    2” dobinson coils, terrafirma shocks, HD steering arms, diff guards, rocksliders, domin8r winch, tank guard

  2. #2
    Join Date
    Nov 2014
    Location
    Sydney
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    G'day.
    Common fault. The sensor needs an earth connection as well, usually via the adapter fitted to the engine block. Don't use Teflon tape on the adapter/sensor as this will insulate the electrical connection. Always check you have zero ohm continuity with the sensor case and engine block and negative battery connection with these single wire sensors.
    Hope this helps.
    Chris

  3. #3
    Join Date
    Sep 2015
    Location
    In the shed or 1000km from home
    Posts
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    Thanks! I will check the continuity between the sensor and block.

    I also found out from a SAAS gauge troubleshooting manual that the problem could be:
    "-sender signal wire is too long ortoo thick-wire thickness must not exceed 20AWG"
    So i tested a long bit of wire that was thinner and got the correct pressure readings. So it would appear that the wire i was using was actually too thick and had not enough resistance! Didn't see that one coming!
    97 Disco 300Tdi, front & rear diff locked, hybrid turbo, full width intercooler, cranked front & rear arms,
    2” dobinson coils, terrafirma shocks, HD steering arms, diff guards, rocksliders, domin8r winch, tank guard

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