Sharing the stock coolant sensor with MS

[wpendl1]

I have a MS I version 3 board. Since installing it, the cooling fans do not come on by themself. If I unhook the wire from MS that is tapped into the stock ECU harness the fans will come on when the engine gets hot, however then I don't have a coolant reading to MS...
My MS has a 2.49K resister in the R7 spot. I did search and came up with contradicting thoughts. Some posts say that if you are T-ing into the stock ECU wire for CLT temps, you should not have a biased resistor on the MS board in R7.
So, trying to get MS to read a proper temp, and still have my fans controlled by the stock ECU, I used a second temp sensor. My car is a 96, but I have a 93 coolant passage where the CTS screws in (so I have two diffrent CTS). So I decided to use a second CTS dedicated to MS. The Sensor that was there already has a diffrent resistance value than the one the stock ECU uses. So I pulled it out, and put in a second CTS of the same type the stock ECU uses. Wired one side to ground, and the other to the MS wire harness. But now the temps in MS are diffrent!

Do I need to change the resistor in R7 when not T'd in to the stock ECU?
If so, does anyone know of hand what resitor I should use?

I tried to edit the values using Easytherm, but had very bad luck. I put in the values I got by taking ohm readings at diffrent temps. 44, 70, and 200 degrees, had easytherm create new inc and s19 files, then tried to download the s19 file to the MS box. After doing that, and then reloading my MSQ, the temps were still off... Far off.

Thanks all for you help!

[shaodome]

Writing a reply in a minute...let me finish my lunch bRb

[wpendl1]

How long is your lunch??

[shaodome]

Yah...kinda got busy...then forgot...then remembered...then got lazy...

Anyways...

The R7 resistor needs to be there if you are not T'd into the line with the stock computer. If you ARE sharing the sensor then you can only have ONE bias resitor in the circuit (well the ECU uses two, but for simplicities sake lets use one), so the other must go bye bye.

If you share with the stock ECU, REMOVE R7 (DO NOT JUMPER). That is the only hardware mod required, the rest is firmware/software.

You will need to recompile a new s19 file (flash file) and burn that to the MS. When you download code from the Extra site it comes with a SRC (source) folder. In that folder are several INC (includes) files that get combined into the final flash. The one for the coolant temp sensor is Thermfactor.inc.

I have attached the modified thermfactor.inc for you to use (included on the CDs I send out).

Place this file (ovewriting the old) in the SRC directory and run the compile.bat. This will create a new s19 file for you...it will place it in the src folder as well. Thus, if you use the MS downloader (download.bat) you need to either direct it to that file or replace the original s19 in the folder above. Flash it to your MS1 chip.

That is HALF the battle. Now MS will use the stock ECU bias resistor and be calibrated for it.

The other half is telling Megatune you changed the values. All this involves is copying the SAME modded thermfactor.inc to the mtcfg folder of your current project directory. So if you are only using the basic MS (and aren't working on different projects) the car1/mtcfg folder will do fine. Place the thermfactor.inc there and enjoy.

[wpendl1]

Wow! That's wonderfull! Thanks.
I'm thinking, since I already ran the wires for the additional CTS, I will just stick with using that one. So now, I will need to find out the proper size resitor to use for the stock 93 style CTS. The green one, not the gray one. They I will need to build new inc files, s19 file, and download to MS. Then copy the inc files to the source directory.
Do you know off the top of your head what size resistor is the proper one for the 93 style second CTS?

Thanks again for your help!!

[shaodome]

I do not know about the 2nd coolatn temp sensor. as for wiring, just do it at the ECU and share the stocker This will probably take YOU 15-20min.

[wpendl1]

True. Thanks again!