Adding a resistive sensor
 

So I am attempting to add a resistive coolant temp sensor from a saturn for my oil temp. I had found it online, on msextra I think, where people recommended using it. However, my understanding was I just put 1 lead to ground and 1 lead to an analog input (EGO2) on the ms3x card. Set to GM calibration. Did not work, and the values are crazy, and jumped a lot. Do I need to a 12V pullup with a 1k resistor to make this work? Or is there something else I am doing wrong?

Yes, and they've made this easy for you.

(Oh, and it's 5v, not 12v. If you apply 12v directly to a CPU input pin, you'll probably kill the chip.)

(And you should use 2.49k rather than 1k, as that's the de-facto standard for MS pullups. This affects the calibration.)

Here's the MS3X schematic for the analog inputs:

https://www.miataturbo.net/attachmen...1&d=1432485570

R65, 66 and 67 are pullup resistors. Now, normally pullups aren't needed for inputs from things like MAP and EGO sensors, as these devices output their own positive voltage. So their presence on the schematic might seem odd until you look at the actual board itself:

https://www.miataturbo.net/attachmen...1&d=1432485703
(Image from DIYAutoTune)

See those holes labeled R65 through R67 right in the middle of the board? Very nice of the designers. Recognizing that people might want to use these inputs for other sensors, they provided a place for a pullup but left it unpopulated, as its presence would have interfered with the devices which those ports were originally intended for.

So all you gotta do is stick a 2.49k resistor into the spot marked R66, and you'll be good to go.

I read this, took the advice, and ordered resistors. But apparently I completely spaced and forgot to say thank you!

Appreciate it Joe.

You're welcome.

Schuyler, can you post the link to the oil temp sensor you're using?

http://m.ebay.com/itm/170849326469?nav=SEARCH

Got it at O'Reily, like that one though.

I'll post here confirming it works when I get the resistors.