newer firmwares and IAT sensors

[AVP]

is it true that the 1.8T audi sensor is not required on the newer versions of vemstune as the old PTC type can read 2C difference (instead of 5C)?

[mattias]

Please explain further what your point is exactly.

[AVP]

well,
on audi engines, there is the old type IAT sensor which requires an extra resistor which is piggybacked in the ecu to allow for the sensor to operate(otherwise it will get damaged). This IAT sensor is not very accurate, doing jumps of 4-5C at a time. So lots of VEMS users in audi cars, switch to the 1.8T engined IAT sensor which has an accuracy of 1C, but the extra resistance has to be removed from the ECU prior to connecting it to the car, and obviously when uploading the firmware, the correct temperature files need to be used.

Recently a friend of mine asked about upgrading to this sensor (im about to in the future) and got some answer saying that in 1.1.7x and 1.1.8x firmwares, the IAT resolution is 2C no matter which IAT sensor is used out of the 2. Both need the resistance removed, and the proper files uploaded with the firmware.

So my question was going to be, if people are aware of this, cause that will save me some extra £££ removing the inlet manifold to make the modifications for the 1.8T sensor. (having said that, the 1.8T sensor is much cheaper to replace if damaged than the old type that audi cars used).

[mattias]

I have no idea where you get this information.

The ECU is not damaged from using a PTC sensor. There is an "extra" resistor piggybacked but that is just the simple fix (2700+510=429 Ohm) required to match the resistance in the sensor to get a decent input voltage range for the A/D input on the ECU. The A/D calibration curve is then easier to make and of better resolution, this is the standard method.  If you remove the piggybacked resistor you will use the default impedance match (2700 Ohm) for an NTC type sensor. As far as I know the same calibration curves and A/D hardware has been used with all firmwares, so no increased accuracy is possible with the most recent firmware.

The sensor installed on old Audi turbo engines is of PTC type and should only be used in an emergency,  I tried once many years ago and gave up and installed a modern open-element NTC sensor. The stock PTC sensor is too inaccurate, both by it's resistive properties and it's mechanical design.  It does it's job well with the stock ECU since the fuel calculation is based on the hot wire "MAF" method, if I was to speculate about why a PTC sensor was used it's because of cost and not needing any better accuracy, it only uses a small part of the A/D voltage range for the -40..+101C range.

With VEMS you are using Speed-Density which relies on manifold air pressure and intake air temperature, both must be quick to react and accurate to be of any use. This means using a NTC sensor with an open element design, like the modern turbo engine sensors. You can use the stock mounting location and simply drill and tap for the common M14x1.5 thread that the webshop sensor uses, I have always done this operation with the intake manifold in place, a vacuum cleaner will take care of aluminum shavings.

[GintsK]

I never use PTC! Because in our case both are important - accuracy and response.
My solution is NTC from damaged BOSCH hot film air mass meters or fast IAT sensor from webshop soldered in place of the PTC.

[AVP]

i see

well when i first bought vems i needed to be able to switch to motronic at any time simply because i was learning how to use and map vems. now, i dont need it anymore, so i can switch to NTC type sensor. I am too afraid of aluminium fragments going into the engine, so since i will be taking the inlet off for a phenolic spacer installation, i will have it done then. The reason i wrote this was because recently this is what we were told from a question that was asked in the wiki. By the way the PTC type sensor is way more expensive than the NTC type sensor bought from audi.

here is the link:  http://www.vems.hu/wiki/index.php?page=MembersPage%2FBillman

[AVP]

did anyone see the link?

[mattias]

I read it, it doesn't say anything about ECU damage.

The big point here is :
-  The PTC sensor is useless since it's not accurate or fast enough.

Any difference there may be with a more recent firmware can not improve this situation, and I was not aware that there was any difference in the sampling of the temperature since the A/D hardware is the same and always has been.

[AVP]

good,
i probably phrased it wrong regarding the ECU damage, but that was never my question. The question was that since this new information was available, would there be any need to change from NTC to PTC, and thank you as well as the rest, i got my answer.

It appears though that so many different things are happening from so many different people regardin the development of VEMS which is why it is so hard to keep up.

Nevertheless, nice to know!

[mattias]

I don't know if it's hard to keep up with development of anything, the simple matter is that the stock PTC sensor sucks and a modern open-element NTC sensor rules. 

[billman]

Is there any picture of the where the 2700+510=429 Ohm resistors are located in the Assembled ECU so i can remove them?

What IAT-flash do you recomend for the NTC? Do we know the part number for the 1.8T sensor so i dont have to wait a week to get the Webshop item?

[billman]

Does Bosch 0280130085 sound right?

[Erikk]

Is there any picture of the where the 2700+510=429 Ohm resistors are located in the Assembled ECU so i can remove them?

http://www.vems.hu/wiki/index.php?page=MembersPage/MarcSwanson/MotronicAirTempMod

[billman]

Nice thanks!

[billman]

I never use PTC! Because in our case both are important - accuracy and response.
My solution is NTC from damaged BOSCH hot film air mass meters or fast IAT sensor from webshop soldered in place of the PTC.

Hi,

do you have any pictures of this. I bought a 1.8T IAT sensor but since the connector looks in the top direction and not to the side and it also the plastic is in the way of the air i was wondering if i can simply solder the new resistor to the old sensor housing without issues.

thanks

here some pics of the two: