# A Question about Intake Air Temperature Monitoring in Forced Induction Setups



## [email protected] (Jul 1, 2009)

The 07K 2.5L engines fitted with MAF sensors have their intake air temperatures read at the MAF. There's a small thermocouple wire right on the sensor that feeds IAT info to the ECU. This info is used by the ECU in its load calculations and ignition timing advance mapping. But this sensor's placement isn't very good for modded engines with turbochargers. That's because the IATs seen at the intake manifold are going to be affected by the heat from boost and the cooling from the intercooler. So what goes into the MAF sensor is almost certainly not what's going into the intake manifold.

While it's handy for testing purposes to see how a turbo performs at a specific value for the air it sees, it's less than ideal for the motor's engine management. For example, here are two logs taken on days where the ambient temps were 30˚F different. 











One day was 50, the other 80. But because the temperatures inside the engine bay were more or less consistent, the benefits of lower post-intercooler temps are not being registered. The sensor in the 07K's MAF is a simple thermocouple. Is there any history of figuring out a way to move the sensor into the manifold plenum, as done on all stock turbocharged cars? It seems this is an important question if an FI 2.5L is to run safely and efficiently.

Thx


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## killerbunny (Jul 10, 2008)

People running a non stock maf put an external IAT sensor in the intake manifold. You could use a sensor out of an earlier VW (MK3 vr6 or MK4 1.8t are possibilities) or anything else like a GM sensor as long as you can tune for it. If you wanted to you should be able to use these sensor and the stock maf, just connect to the cars IAT wire (maf connector) to the external IAT sensor. IIRC it should be pin one on the maf connector. I have not seen/heard of anyone moving the stock IAT senor from the maf.


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## [email protected] (Jul 1, 2009)

killerbunny said:


> People running a non stock maf put an external IAT sensor in the intake manifold. You could use a sensor out of an earlier VW (MK3 vr6 or MK4 1.8t are possibilities) or anything else like a GM sensor as long as you can tune for it. If you wanted to you should be able to use these sensor and the stock maf, just connect to the cars IAT wire (maf connector) to the external IAT sensor. IIRC it should be pin one on the maf connector.


Exactly. There is a wire which sends back the 0-5v signal for the temperature signal. And NothingLeavesStock very clearly labeled those wires during the installation of this turbo hardware. So I think the next question is whether an IAT sensor such as this commonly-available one from the 1.8T...



















...might not do exactly what the sensor element in our 07K MAF does. The 1.8T part has two wires, presumably for 5v source and for the return signal. I think it's worth giving it a try.

Thx


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## killerbunny (Jul 10, 2008)

The other wire should be a ground. I believe on the maf connector pin one is the IAT, and then pin 3 would be the ground. I actually use a 1.8t sensor on my car, you should be good, but I am not sure if the stock IAT and 1.8t or VR6 IAT scale the same.

Edit: Also curious how/where IATs are found in the MAP only cars. Wonder if it is built into the MAP sensor, which is already in the intake manifold.


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## thygreyt (Jun 7, 2009)

i have an 09... We get the temp measurements on the MAP sensor by the manifold, therefore all temp changes are measured, accounted and maps are accordingly modified in order to take advantage of the gains.

How the MAF cars do it, i dont know. but it sure seems interesting to find out!


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## [email protected] (Jul 1, 2009)

thygreyt said:


> i have an 09... *We get the temp measurements on the MAP sensor by the manifold*, therefore all temp changes are measured, accounted and maps are accordingly modified in order to take advantage of the gains.
> 
> How the MAF cars do it, i dont know. but it sure seems interesting to find out!


Well now THAT's interesting. I wonder if the Mk6 cars' sensor is compatible with the Mk5 cars' intake manifolds. If so, perhaps a re-route of the IAT signal wire is all that's necessary.


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## thygreyt (Jun 7, 2009)

[email protected] said:


> Well now THAT's interesting. I wonder if the Mk6 cars' sensor is compatible with the Mk5 cars' intake manifolds. If so, perhaps a re-route of the IAT signal wire is all that's necessary.


MAF cars have a map. Just check compatibility of the maf's map, vs the map on the map only 5 cyls, and if the same, then a spliced wire might just solve the issue (along with the new sensor).. and this is assuming that both sensors work on the same voltage input/conversion/output


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## [email protected] (Jul 1, 2009)

thygreyt said:


> MAF cars have a map. Just check compatibility of the maf's map, vs the map on the map only 5 cyls, and if the same, then a spliced wire might just solve the issue (along with the new sensor).. and this is assuming that both sensors work on the same voltage input/conversion/output


The only way to know is by trying. ECSTuning sold me these three parts:





























It's just less than $100 for the needed parts. If it works, that's a great value.


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## [email protected] (Jul 1, 2009)

OK. Step one is done. The new sensor arrived from ECSTuning and I took these pictures during the swap:


New at left with the original











The shiny bulb object inside the sensor surround is the temp sensor






















Both parts have four pins for the connector. But the old one clearly doesn't have a temperature sensor











The new MAP sensor installed. Direct fit. To the right you can see the stock harness connector lacks a pin for the temp signal











Sensor in place











With the new sensor in, the car functions like normal. No codes. The MAP sensor at idle returns these numbers over the OBD port:


```
; Time: seconds		
; Intake manifold absolute pressure: kPa		
; Engine RPM: RPM		
;		
Time	Intake manifold absolute pressure	Engine RPM
234.4	72	865
235.5	72	1016
236.6	74	1548
237.6	50	1718
238.7	50	1805
239.8	55	2126
240.8	71	2678
241.9	51	3174
243.0	39	1871
244.0	57	1109
245.1	66	901
246.2	71	888
247.2	72	880
```

So I believe the new sensor works as a replacement for the stock unit. The next question is whether the new sensor's IAT readings are compatible with the Mk5's ECU.


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## slowgti (Jul 15, 2003)

Are you sure it's a 5v sensor and not a ntc thermistor, aka a resistance sensor for iat?

Edit: you might be able to run one of these on the factory plug with some programming 

http://www.bmotorsports.com/shop/product_info.php/cPath/129_143/products_id/1721


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## [email protected] (Jul 1, 2009)

slowgti said:


> Are you sure it's a 5v sensor and not a ntc thermistor, aka a resistance sensor for iat?


According to Bosch's tech docs for both the MAF sensor and the MAP sensor , they both use a NTC resistor as the sensing element for temps.

So now that I've covered the suitability of the Mk6 MAP sensor for its main job -- monitoring intake manifold absolute pressures -- here's a quick DIY from ForceFed Engineering's Ed Woolsey. It turns out the stock plug can stay put, by simply adding a pin and wire to the assembly. Have a look:







With that wire now running from the temperature sensor's output, we simply cut into the harness where the OEM sensor's signal passes and patched in our new wire.

How does the new assembly compare to the stock element? Here are the two readings while at idle:


Stock sensor at the MAF housing:











Mk6 sensor at the intake manifold:











After a 10 minute warmup, here is what the sensor is reading over the CAN bus:











And here's a look at the wiring (which I'm sure could be improved upon from a visual standpoint):











The next test is to see exactly how the wide open throttle IAT measurements behave versus before. We'll pull some data logs this evening.

:beer:


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## killerbunny (Jul 10, 2008)

What is the limit in the pressure reading on either map sensor?


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## [email protected] (Jul 1, 2009)

Based on Bosch's published documentation I believe it's 20mbar - 2500mbar absolute pressure for all 07K engines.


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## thygreyt (Jun 7, 2009)

Great!! This is awesome


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## [email protected] (Jul 1, 2009)

thygreyt said:


> Great!! This is awesome


GreyT, you totally get a Gold Star for this one. Because take a look at the graphed results:











A simple breakdown of what this graph illustrates is this: the red lines represent values for ambient temps and for "intake temps" collected from a stock configuration. The BLACK lines show ambient plus the much more accurate, no-quotes-needed intake temps from a sensor in the intake plenum. The intake temps are no longer skewed by the heat of the engine bay environment. They're far more accurately showing the intercooler's benefit in bringing temps down virtually to ambient.

In other words, we now can see we have a good intercooler. But the other benefit is that in cases with a lousy one, the ECU will know it. Not a bad return on less than $50 parts investment.

Next step: install a post-throttle body water methanol injection system to see just how well that relocated sensor pays off.

Thanks to everybody in the forum for contributing to a nice, affordable mod.

dh


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## thygreyt (Jun 7, 2009)

"i love it when a plan comes together".

I honestly love it when a technical thread does a positive contribution to an overall concern.


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## SocoJoe (Jul 4, 2009)

👍🍺

Sent from my phone


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## [email protected] (Jul 1, 2009)

A quick follow-up to this:

The sensor's compatibility with the Mk5 ECU in the car is perfect. The car's been run and re-run through the engine range at various boost without any issues. Without question this is a worthwhile and affordable "must do" task for any forced induction project. It can simply be ganged to the process of modifying the PCV venting system on the intake manifold, also a necessity for turbocharging this motor.

The temperature sensor's performance is a bit slow. I'm not seeing rapid changes in readings during pulls. But I do feel it's giving the ECU a much-more accurate picture of true intake temperatures than the MAF housing location can.


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## mjb8482 (Mar 4, 2008)

Great work, guys! I definitely want to do this on my car. Can you show where the new wire splices into the harness? Does it eliminate the temp sensor in the engine bay? (The one that was mounted to the stock intake). Thanks!

EDIT: I take back my question--looks like you just splice into the MAF sensor harness at pin 1 and good to go. Please correct me if I have this wrong.

EDIT:
For reference, here are the ECSTuning part numbers:
Wire = ES#265439
MAP Sensor = ES#2678229

Sent from my iPhone using Tapatalk


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