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oem fuel level sensor

MoTeC M1 Software Tutorial

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Hello.Ihave motec m150 and c1212 display. Ineed calbrate the oem fuel level sensor my car is mazda rx7 1994 . And this is the sensor ohms .

7.4 ohms when full, 75.9 ohms when empty, 31.5 ohms at halfway.

wiring is going out from stock cluster wiring to ecu AV6

Iwant know what to put in sensor setup






and for the dash manager setup have 3 methods

And im select the

*variable resistance

what should iput in the calibration table


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Is there a reason you don't connect to a temperature input on the C1212? That would be the best, since the calibrations in the dash can be non-linear, and you can calibrate in resistance (and it has a built-in pullup resistor)

Next best would be to connect to AT input on the ECU. That way you could take advantage of the built-in pullup resistor on AT inputs.

BUT, since you wish to use an AV input. You will need to wire the ground-side of the sensor to a 0V input matching the 5V you choose (one side may be grounded to the chassis already, so you can then leave this off and live with the slight error), the signal side needs to be connected to both AV6 as well as a resistor that has the other side connected to a 5V source (5V A, B or C on your M150 - this is your reference). The value of the resistor could be a 1k ohm 1% resistor to match the one on the AT inputs, or you could use a smaller value to give you increase resolution (although most OEM sensors seem to be discrete values with 8 or 9 steps these days).

Knowing the pullup resistor value and the voltage source, you can calculate the output voltage (what the M150 measures), using the voltage divider equations (here's a page to help you do the math): https://ohmslawcalculator.com/voltage-divider-calculator.


Do you currently have the sensor wired into AV6 in the M1?

I have attached a wiring diagram that shows how a variable resistance sensor needs to be wired into an AV input to allow for that sensor to be used. Using a 270 ohm resistor will give a voltage range into the input of around 0.12V to 1.1V for the full range of the sensor, without drawing too much current from the 5V supply.

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