Coolant sensor readings

[Robert Spencer]

I am using the CB Performance 7132 coolant sensor in my ACVW. MT reads 80 degrees when engine is 40 degrees. I have used the thermister calculator and used the resistance figures that came from CB. 185 at 210 deg, 3400 at 70 deg, and 7500 at 40 deg. This did not change the readings at all. As you can guess, this throws my idle steps way off. How can I cure this issue? Thanks.

[Matt Cramer]

What value are you using for the bias resistor number?

[Robert Spencer]

Hi Matt, I will look this evening. I believe it is the default number as I havent changed that. Thanks
Bob

[phj420]

Bob, I replied to your question on my project page here: http://www.msruns.com/viewtopic.php?f=88&t=22767

seeing that you have started a topic on this sensor, I figure this is the better place to post the information.
You asked me:

You state that you are using a CB CLT sensor. I am also using this and have found that the temp in MT reads 80 Deg when the engine is 40Deg. CB gave me these numbers for their sensor. 185 at 210 deg, 3400 at 70 deg, and 7500 at 40 deg. Are these the same as yours? This is making my IAC valve work wierd. Thanks.
Bob

I replied:

CB gave me those same numbers, however, the ones that I entered into megatune were a little bit different. I measured the resistance of the sensor at three temperatures: at 65 degrees F i got 2333 ohms. At 35 degrees i got 3872 ohms, and at 198 degrees I got 274.5 ohms.

The 35 degree resistance was a little bit different than the values that CB gave me. I went with my actual resistance results in the end and I have found that the sensor is quite accurate.

Perhaps you should try and measure the sensor's resistance at different temperatures and post your findings here as well.

a guide to measuring the sensors resistance is here:http://www.DIYAutoTune.com/tech_article ... lation.htm

[Robert Spencer]

Thanks for the reply,
I used the same method as you discribe when I set up the MT. I may still have the old numbers somewhere? I notice that after I input new numbers in the thermister table and come back later, that the old default numbers appear in the table. Is this normal?
Bob

[phj420]

I notice that after I input new numbers in the thermistor table and come back later, that the old default numbers appear in the table. Is this normal?
Bob

Yes that is normal, The values are burned to flash, and are not kept in megatune. You need to make sure that you burn the values that you enter, or they will not be saved.

Are you saying that you already filled in your recorded resistance values in MT and re calibrated your MSII and you still came up with the discrepancy? Maybe you typed something in wrong. You should recalibrate the CHT sensor and see if that fixes the high read at 40 degrees.

[Robert Spencer]

Matt,
I have 2490 for the bias resistor value. Is this correct?
Bob

[Matt Cramer]

Matt,
I have 2490 for the bias resistor value. Is this correct?
Bob

That is the correct value unless you have changed the resistor in the ECU itself.

[Robert Spencer]

That sounds good. I will use some numbers from another squirter that are working for his VW and see how that works. If I can get the temps and the IAC steps working together, I think I am very close to having everything else where it should be.

[Robert Spencer]

Hey phj420,
Thanks for the info. Your numbers put my temp readings spot on. Now if the IAC would cooperate, life would be great. Again thanks.
Bob

[phj420]

Bob,
Glad you got it working. I found that It is easy to have a typo when entering the information for the sensor calibration. This will only throw the curve off over a third of the range.

I posted a reply to your IAC problems here: viewtopic.php?f=29&t=27717

You can make it work too.