Coolant Reading off

[Herbst]

When I installed my new injectors, I accidentally cut the thermostat wires and after rewiring through trial and error, the temperature readings on tuner studio are very far off. At normal operating temperature, tuner studio shows I have a temperature of about 105 F when its normally 190 F. My best guess is I may have burned up one of the capacitor in the CLT circuit, either C6 or C7. I took it apart and nothing looked burnt, but I wanted to double check before I start desoldering and replacing. I have a MS3X and my car is a 1997 Mazda Miata. Currently I just adjusted the thermistor table based on the analog gauge so that the fans will turn on when they are suppose to. I changed the 176F from 330 ohms to 1700 ohms. And adjusted the other two values accordingly.

[billr]

It should be impossible to hurt those caps with any voltage near the nominal 12V. Remove the harness connector from the CLT sensor and do few meter measurements:

1) Key-off, MS ground to one harness socket should be 2499 ohms (assuming R7 is the standard 2.49K)
2) key-off, MS ground to the other harness socket should be near-zero ohms
3) key on, MS ground to the first (2499 ohm) socket should be 5V

Another fairly easy check is to connect the MAT sensor to the CLT input, and vice-versa; see if the problem follows the input or follows the sensor. Little "adapter cables" are pretty easy to make up if those sensors use different connectors.

[Ted75zcar]

Disconnect the wire to the sensor and measure the resistance to chassis ground. Do this at 2 different coolant temperatures and compare it to the Miata resistance curve.


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[Ted75zcar]

You can alternatively measure the voltage when connected and calculate the resistance with the resistance divider formula, using the pull up resistance in your MS as "R1"


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[billr]

This is a 1-wire sensor? Check grounds, especially from engine to MS. Maybe I'm confused, though, as the OP originally stated: "cut the thermostat wires"

[Ted75zcar]

Yes, miata CLT sensor is 1-wire


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[kjones6039]

Sounds as though the op may have cut more than 1 wire! Lord knows what it may be connected to now!

[prof315]

Yes, miata CLT sensor is 1-wire


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No it's not. The 1 wire temp sensor on a Miata is for the gauge NOT the ECU

[Ted75zcar]

I stand corrected, it is a 2 terminal device.

It is still simply a ground referenced resistive sensor and can be tested as such.


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[billr]

So... is the "ground reference" in your install now at an MS DB37 ground pin, or to just some other handy ground?