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Davets

Rb26 Air Temp Sensor Upgrade For Power Fc

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Hi all,

This is something I’ve been meaning to post up for a while now to give something back to the hive of quality information that is SAU.

Anyone who has tried to tune an RB26 engine is aware that the standard air temperature sensor is completely useless for measuring actual air temperature. No doubt it works great as a water temperature sensor (for which it is also used in the RB26) but why it was chosen to measure air temperature is beyond me. It responds extremely slowly and in the factory position measures nothing more than the temperature of the plenum. I’m sure the smart people at Nissan new what they were doing, but for the aftermarket street tuner it isn’t particularly useful.

For those restricted to using the Power FC, even with the Datalogit, there is no ability to alter the resistance vs temperature curve for any of the measurements and, as such, cannot easily swap over to a modern sensor that responds at a reasonable rate.

The method I propose involves the use of a Delphi Air Temperature Sensor (GM Part # 25036751). These are very common and used on a wide range of cars, hence they are cheap, reliable and easy to obtain. The resistance vs temperature curves don’t match but I have found with the addition of the correct resistor in parallel it is plenty good enough. Originally I was planning on adding another thermistor in parallel but found that this technique provided good results over the range I was concerned with and keeping things simple has its advantages.

I measured the resistance of the factory RB26 sensor in 5 degree increments over the range of 0 to 90 degrees Celsius. These where graphed and compared to the known resistance vs temperature curve of the Delphi sensor. Attached is an Excel spreadsheet and also the supplied data sheet for the Delphi sensor.

The majority of what is listed in this spreadsheet is self-explanatory, but the key part to pay attention to is the fair right hand column Temp Error, which shows the resulting error in the temperature measurement. The outlined box above, which currently is set to 14.2, represents the resistance in to be added in parallel. This 14.2 value can be changed and the effect shown numerically in the Temp Error column and visually on the graphed curve shown in purple.

The value of 14.2k Ohms is the one that I used and it worked great for me. You can see from 5 to 60 degrees the error is less than 1, up to 80 degrees it is out less than 5. After that the error starts to run away a fair bit, but personally I haven’t measured intake temperatures of over 60 degrees C.

It’s also important to move the sensor as to not be heat soaked by the plenum. I welded a mount into the steel piping, just after the intercooler.

I know back when I was first trying to fix this problem I searched long and hard but didn’t come up with any answers. It annoyed the crap out of me while I was attempting to get a stable, consistent tune that performed well in both hot and cold conditions. I’m sure there are many other methods of addressing this issue, but this how I approached it and it worked just fine for what I required of it. Hopefully this info helps some people out.

Cheers,

Dave.

post-42333-0-09878500-1351055450_thumb.gif

GM Air Temp Sensor Calibration.pdf

Standard RB26 vs Delphi Sensor.xlsx

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Excellent work, i just figured nissan had heaps of spare3s, and decided to give a free spare water temp sensor to each gtr owner.

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good work

cant download the 2nd file as it doesn't show a link, so how much degree's C is the sensor out from the rb26 sensor?

also can the sensor above be used to display onto a gauge as i'm currently using a ecu coolant sensor to display to a gauge?

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Thanks guys, no problem. SAU helped me out so many times it's good to be able to contribute.

black bnr 32:

Yeah, sure I’ve done some tuning with it. Set it up about a year back and it made a world of difference to my tuning accuracy. Best part was the ability to pull out timing in the hotter weather (although sometimes really cold weather can’t take as much timing as you may expect). To confirm the sensor was reading correctly I inserted a thermocouple into the intake pipe and compared the 2 measurement in a series of different operating conditions, at steady state they were within a degree over the range I checked (although the sensor doesn’t respond quite as fast as the thermocouple ofcourse). Recently I’ve changed to a vipec/link and still use the exact same sensor, just with the parallel resister removed, but still quite impressed with how well the power fc (mine was djetro) works and how easy it is to tune (with datalogit ofcourse, handcontroller’s a joke).

.:::JAP TAXI:::. :

I checked the excel file and it downloaded fine for me, possibly try a different browser. Between 5 – 60 degrees Celsius it was out from the RB26 Sensor by under 1 degree. I’m sure the repeatable accuracy of the factory sensor is over +/- 1 degree anyhow, so we might as well consider it spot on. Sure it can be used to display on a gauge, but for you to get the correct reading the resistance vs temperature curve must match.

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thanks for the reply. I'm using a d jetro and datalogit as well, and i think I'll give this a try.

I mean, IAT is theoretically a critical part of calculating air mass with a speed density system. The slow response and heat soak of the stock part CANT be ideal.

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figure i'll post in here as there's not much of this going on.

i've bought a gauge that comes with a temp probe, so i've removed probe and connected the gauge wires up to a sensor ( 2 pin ecu coolant type).

now said gauge over reads by about 100 deg c, therefor i've added a resistor/s in series on the senor wire to bring the gauge readings down with what it should be.

my problem is that the temps will get stuck and not go lower once the temps change from said sensor

any help, electronics ain't my strong point :glare:

Edited by Dan_J

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just wanted to bump this thread for some results. With the stock sensor, I see about 17*C of heat soak. The new sensor sees virtually none. So, my actual air temp is as much as 17*C different than what the stock sensor reads. I installed the new sensor in the plenum.

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hey mate,

great thread, do you have a diagram for the size and wiring of the resistor.

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Hi, sorry to message on such an old post but I have a couple of questions as I've just bought one of these sensors to do some DIY myself.

  1. If I were to place this just after the intercooler, which is pretty cold, but the plenum still gets hot, would the air not heat up by the time it reaches the cylinders and get worse as the plenum gets hotter?
  2. I have water injection on my car so if I were to put the temp sensor before this, I would be, as expected, getting readings that are higher than what goes to the cylinder however this value would be constant when at WoT, thus tuneable for those cells; is my logic correct there?

Many thanks!

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Such a legend this guy.

I have found the same sensor characteristics as the delphi but in a smaller frame sensor....

https://www.efihardware.com/products/1623/air-temperature-sensor-motorsport-series-18-bsp

buy some Nissan connectors, crimp in same resistor as said legend suggested, lathe an adaptor and voila - factory fit!!!

9_zpsae4d5f3c.jpg

Edited by LWO

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From what I undrestood the air temp sensor is used by the ecuto back out timing when the intake temp is excessive

They use it to back out timing and not to add timing so heat soak on the sensor isn't a massive issue

It's a safety feature to protect against excessive intake temp / damaged intercooler / unlimited boost scramble

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