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Thread: Testing Gauges

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    Registered User GILDIA's Avatar
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    Default Testing Gauges

    Hi, does any body knows how to test the OIL/TEMP gauge, i can't get a single lecture from them.

    Thank you
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    72 240z Mexico city
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    Supporting Member EScanlon's Avatar
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    Both require the sensor mounted on the engine for readings.

    If I recall correctly, they are both resistance sensors. As such, if you connect the Yellow/Red wire to 12v+ and the Yellow/White to ground, the gauges should "Max" out, that is, read all the way to the right.

    HTH
    E

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    take the wire off the sensor turn on the ignition. ground the wire gauge should max.

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    beandip beandip's Avatar
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    I wanted to see just what mid range was in lbs. on my oil pressure gauge so I installed a mechanical gage . In my case the mid position reading is close to 50lbs, and 1/4 off the zero is about 25 lbs . this is where my engine runs when at idle and normal temp. The temp gage use either a candy thermometer in the top tank of the radiator or one of the infrared sensors on the market. Either will work fine , just keep the glass from touching the metal of the Rad. Gary
    I'd rather die while I am living than live while I am dieing. CZC 1887 IZCC 12602 Member of NorthWest Z Car Club

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    Registered User GILDIA's Avatar
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    Thank you guys, I will try it, what if when i ground them they wont read? does that mean that I will need a new gauge?
    ---------------------------
    72 240z Mexico city
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    Supporting Member EScanlon's Avatar
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    These are pretty simple gauges, simple analog dials. Check the obvious; power and ground connections. Past that.... you might want to find replacements.

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    Registered User GILDIA's Avatar
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    Thanks E, regarding the power it feeds through the VR, and it just goes directly to the oil and temp sensors.
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    72 240z Mexico city
    Pertronix Ignitor + Flame Thrower Coil

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    Supporting Member EScanlon's Avatar
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    Exactly, the gauges make ground through the sensors in the engine block. As the resistance of the sensors changes the current flow changes as well causing the gauge to deflect more.

    An interesing note here, I don't have the information as to whether the sensors increase or decrease resistance as the pressure/temperature changes. This might be a good point for someone to point out.

    Hope this helps
    E

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    Quote Originally Posted by EScanlon View Post

    An interesing note here, I don't have the information as to whether the sensors increase or decrease resistance as the pressure/temperature changes. This might be a good point for someone to point out.

    Hope this helps
    E
    E, I don't have a lot of experience working with or testing these gauges but I know that less resistance will result in a higher current flow, which will make the gauge read higher as the temperature or pressure rises. So yes, I would say the sensors decreases resistance as the temperature or pressure rises.
    Last edited by geezer; 05-26-2008 at 11:37 AM.

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    Registered User GILDIA's Avatar
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    So, if i ground the sensor wire, i should read maximum?
    ---------------------------
    72 240z Mexico city
    Pertronix Ignitor + Flame Thrower Coil

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    Supporting Member EScanlon's Avatar
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    Yes.

    What I was asking, that Ron answered, was whether anyone knew whether the sensors increased or decreased their resistance as the temperature/pressure went up. Since higher temp usually results in higher resistance (at least as far as electricity is concerned) it's not automatically intuitive.

    E

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    Registered User GILDIA's Avatar
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    I just ground the but i am not getting any lecture from it, do you know what is the voltaje I should get from the VR...
    ---------------------------
    72 240z Mexico city
    Pertronix Ignitor + Flame Thrower Coil

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    Registered User GILDIA's Avatar
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    I just measure at the VR and i get 13.9 Volts to the gauge, and i also measure the resistance from the temp sensor and i get around 200 ohms and it decreases at time pases by, but i dont get a reading at the gauge, I am going to open it and clean it
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    72 240z Mexico city
    Pertronix Ignitor + Flame Thrower Coil

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    I'm not familiar with the testing proceedures used for these gauges and don't know what the voltage reading should be at the VR (limiter), but if you feed it a ground in place of the transmitter wire it should peg the needle. If not I would suspect the gauge itself as being at fault. That's just my guess. You need to hear from someone that is familiar with a tried and true method of testing these.

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    ...around 200 ohms and it decreases at time pases by
    That is the typical property of an NTC type sensor, Negative Temperature Coefficient.
    Simply put it means that the sensor resistance to earth reduces as the temperature increases.
    The attached thumbnail shows the behaviour of such a device.
    Don't expect these values to be exactly those of your sensor but it is what it should do with temperature variations.

    The oil pressure sensor is usually exactly the opposite.
    As the the pressure increases the resistance of the sensor also increases, Positive Pressure Coefficient.
    That is why unplugging the sensor wire, introducing maximum resistance to earth, results in the Oil Pressure gauge maxing out.
    The typical symptom of a faulty oil pressure sensor as it deteriorates, is the wiper inside it wears an open circuit at the "normal pressure" point of the sensor resistance coil.
    That causes an intermittent open circuit to be read and the gauge needle jerks and jumps about the faulty position.
    Usually the only remedy is a new sensor since they are not repairable to my knowledge.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	NTC graph.jpg 
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    Nissanman - just trying to help
    http://nissanman.shutterfly.com/action/

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    I guess i am going to need a new gauge, I tested it with an external source (12 volt) and the gauge skoke start ti get out of the gauge

    So I made a mistake but i learned from it ...
    ---------------------------
    72 240z Mexico city
    Pertronix Ignitor + Flame Thrower Coil

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