I am very hesitantly posting this as it could potentially cause some ill feelings but this is not my intention so please read carefully.
Over the last few days I have received emails about the intake air temperature sensor and our Alpha-N software.
The questions have arisen due to the release of another companies' MAFLESS tune where they do not use the IAT sensor.
Some of the emails I have received are suggesting that we are for no reason keeping the sensor and one even suggested that we do it so we can make additional sales from selling a kit!
So, I have no choice but to cover this topic and hopefully it will serve to educate those that are interested.
Intake temperature sensors have been on BMW's since the E30/E34 era. They are there for a reason and are an incredibly important sensor.
ECU's have intake air temperature compensation maps build in where the general strategy is to offset the ignition and fuel maps.
As the intake temperature rises the ignition timing is retarded and as the temperature lowers the ignition timing is advanced. At a certain intake temperature the ignition timing is neither advanced or retarded.
This is true for the MSS52 DME fitted to our E39 M5's also.
If you unplug the MAF's you will see that the default value for this sensor is 60 degC.
Below is a test we carried out on a car where we disconnected the IAT sensor.
Power vs Air Fuel Ratio
Power vs Torque
Power vs Actual intake temperature inside airbox (using dyno probe)
You can clearly see that disconnecting the inlet air temperature probe adds quite a bit of fuel and retards at the very least in this situation upto 5 deg ignition timing (which is alot!). A full 20hp peak comes down so we can easily deduce the IAT sensor compensation maps work and quite aggressively at that....... obviously for good reason!
Now, for us to create a map that does not take the IAT sensor into consideration we can follow many strategies. Not one of them is something we would ever go ahead with because we understand the importance of this vital sensor.
We could simply switch off the fault code for the IAT sensor when disconnected and map the fueling and ignition with the default value left at 60degC or change it to any value we want. However the mapping would only be optimal at the inlet temperature at which we mapped for at the time. As soon as the temperatures change both the fuel and ignition applied would be not be optimal. How far away from optimal would depend on how much difference there is between the temperature at which we mapped at and the actual inlet temperature. The bigger the difference the less optimal the applied fueling and ignition.
With this shown you can now ask the question of how would this effect the running of the engine. Well, suppose we have an actual outside temperature of 40 degC (Some parts of USA and definately the middle east) and the default setting of the sensor was set to say 25 degC. You would have too less fuel and way too much ignition timing. This would lead to detonation and lean running and therefore adaptive values being either very negative of positive.
Now, there is another aspect to this and this is how the actual temperatures change whilst during any normal driving cycle. If you care to log your inlet temperatures at say 25 degC ambient you will see how the temperature swings so massively especially in town driving. Even at a drag strip the inlet temps would rise as the car is stationary to something like 60+degC even with 15degC outside and by the time your at the line ready to go you have completely the wrong fuel and ignition for full throttle driving.
The situation worsens with a power tune because all power tunes will run more ignition timing. You can see where that can lead!
The reverse of this would be very low outside and therefore inlet temps (very cold countries such as Sweden etc) and a default which is much higher. The you have too much fuel and not enough ignition timing.
The fuel for part throttle would eventually work itself out because of the lambda sensors but for full throttle you are in the situation above. Ignition timing would always be offset though.
Basically there is no assumed preset value for the IAT sensor you can set to work optimally under all conditions.
The sensor is critical and must be used!
There are various ways to stop the fault code appearing but all lead to the same situation and as someone who has spent a huge amount of time developing the calibration for the S62 with at least 120 cars worldwide being run on AlphaN.... IAT MUST BE USED!!
If you have the above strategy used in the base mapping then even if you do fit a temperature sensor it's a waste of time because your base calibration is set for which ever temperature the mapping was done for.
If you think it's not important then you might aswell delete the coolant temperature sensors too!!!!!!!
Most people on this board are very intelligent and I am rather shocked to see the correspondence from members here even asking me about this and even more shocked at the ones who have accused our AlphaN setup using sensors which are not actually required and it's all part of a plan to earn a few dollars from a IAT relocation kit!
I hope the above brief explanation puts people's minds at ease and shows that we develop our engine calibrations with the correct approach from all angles and not just from the point of view to 'run' the engine and 'to make power'.
Again, I will mention that the above is no way intended to harm another company and their strategy but is a reply to those that doubt our methods because of how another company has decided to calibrate their version of an AlphaN tune.
All car manufacturers use IAT sensors in their cars and it's not just about emissions as you can clearly see from the above.
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E39 M5 Tuning
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