87 Vette Owner

I have been successfully data logging A/F ratio, RPM, and TPS information using the LM1 Meter and RPM cable. This weekend, I attempted to hook up coolant temp information as well, splicing into the wires going to the CTS.

I did something wrong because I am getting VERY whacky coolant temp readings; when I started the car up, it read something like +400*F and then slowly dropped down to +290* F (basically the opposite direction of the true coolant temp, and nowhere near the true temps as verified by the CTS readings in the datalog).

Does anyone have any experience with this? How did you connect to the coolant temp circuit? If I mistakenly reversed the wires, would that be the reason for these screwy results?

thanks!
Dan

dimented24x7

iTrader: (2)

The CTS is a negative coeff. sensor. At low temps, the resistance is high, and at high temps, its low. At low temps the CTS voltage will be close to 4 or 5 volts while warm, it may only be a volt or so. Check to make sure you have the correct curve entered into the LM1, and that your not tapping off the ground side, but that would result in no reading at all.

87 Vette Owner

I verified that I have the wires hooked up correctly (blk is ground, yellow is voltage to ECM). Interestingly, when I look at the raw voltage data that I recorded, I can see the voltage as you described above; at start up, the voltage starts out at 3.45 volts (cooler) and after about 5 minutes, it settles in at a stable 2.6 volts (warmer).

But, when I put a "check" in the thermocouple box (to convert the data to degrees F, I think), that's when I get the extremely high temp readings. 3.45 volts maps to 650 * F and 2.6 volts maps to 500 * F.

How do I enter the correct curve in the LM1 meter? I looked through the instructions I have for both the LM1 meter and the RPM cable and didn't come across anything that addresses this.

Thank you very much!
Dan

dimented24x7

iTrader: (2)

The CTS is a thermister. A thermocouple will have different coefficients then the CTS will. If theres no option to enter/edit a table or curve (Ive never tried to datalog with mine) then you may not be able to datalog the CTS, or youll have to convert the raw data in excel or something.

87 Vette Owner

I'll contact Innovate Motorsports to see if they recommend anything. There has to be a way . If I learn of anything, I'll post my findings in this thread. In the meantime, I'll try to come up with some type of voltage to temp conversion myself, just to have an idea.

Thanks again for your help!

87 Vette Owner

OK - some digging on the Innovate Motorsports web site turned up this:
http://www.innovatemotorsports.com/r...easurement.php

It confirms our discussion, and shows how to set up the circuit for a data log of temperature. The non-linear relationship between voltage and temp makes a conversion chart a little more difficult.

Maybe I'll give that circuit a try at some point...

dimented24x7

iTrader: (2)

The circuit is essentially already inside the ECM. You just need to convert the data over so its something meaningful other then just a voltage. Just follow the "Calculation of Voltage/Temperature for LogWorks" section. Somewhere around here there are charts showing the resistance vs. temperature for a typical CTS/IAT that can be used in the spreadsheet.

Off the top of my head, this one is really close to the stock IAT/CTS http://www.jameco.com/webapp/wcs/sto...oductId=207466

Im using one of those (cant remember which) as an additional temperature sensor and its a nearly perfect substitute for teh stock IAT/CTSs. You could probably just steal its specs for the calculations.

87 Vette Owner

Will do - thanks again!