Using a Non BMW IAT sensor (HPX)

[xr7dave]

Is there any good reason why we can't use the built in HPX IAT sensor? I tried looking for the transfer function for the sensor in the software but can't find it. I'm assuming it is defined somewhere just like the MAF sensor. The HPX IAT sensor is a simple thermister which seems like the same type of sensor as the BMW MAF uses, so if we could enter the correct values, we should be able to just use it right? Anyone done anything with this?

If that doesn't work, are there any instructions on how to wire an earlier type separate IAT sensor into the MAF wiring?

Working on an 04 ZHP, starting a turbo conversion and wanting to get it running well with the new MAF and injectors before tearing into the rest of it. Thanks for any tips!

[Renovelo]

Theoretically, yes you should be able to use any automotive temperature sensor assuming it's the same type (i.e. resistance based) and voltage range (i.e. 0-5v). Although we haven't tested this ourselves, it should be as simple as wiring it properly and modifying the IAT curve for the MS45 sensor using ByteTuner.

[xr7dave]

Next question then, I spent quite a bit of time going through the calibration and I can't find the transfer function. I got ip_tia__v_tia from the MS Wiki but that doesn't come up in the search, and I swear I went through every function in the entire calibration and I can't find anything that seems to pertain to an iat transfer function. I am sure I'm just missing something but idk.

[Renovelo]

It seems you overlooked it. It's labeled exactly as you said and it's under the "Uncategorized" section in ByteTuner. Use the search functionality again to find it.

[xr7dave]

Yes, I found it thank you. I know this has to sound elementary but I'm having some issues with connecting the SCT sensor so that the IAT functions correctly. I have the car running decently with the MAF, but the IAT is giving me fits. I'm a bit new to electronics specifically but not new to tuning or engine control but the instructions on the wiki call for using a 22K ohm pull-up resistor. I can't get any kind of useful value using 22k ohms. Grounding the SCT sensor and connecting the IAT lead to the other side of it with a 2200 ohm resistor to ground (parallel) gets a room temperature reading through the ECU that's close but is this the right way to wire the pullup resistor, and why am I seeing results with 2200 instead of 22000 like they say? 22K doesn't make any appreciable difference to the readings (-35 vs. -48) at actual room temperature of 19 deg.

Does anyone have a diagram for the more simple minded? lol I'm about to just buy an Audi RS4 sensor but this should work and it's making me mad.

Then, is there a way to rescale the transfer function with the Ford voltages? I'm having a bit of a headache trying to get Ford values that correlate with the stock voltage scale. It seems we should be able to type in the voltage points on the transfer function.

[Renovelo]

We're not experts with this particular MAF and only had one installed for a short period of time on one of our previous shop cars. At that time, we weren't even using the integrated IAT sensor. Without seeing your setup with our own eyes and getting our hands/tools on it, I'm not sure we will be of much help here. ByteTuner allows you to modify the transfer curve values or the voltage axis depending on your needs.

[xr7dave]

Ok, I will look for the function that allows me to change the voltage points.

We are working on an 04 ZHP 6spd manual putting a turbo on it. So far we are just working on getting it running first with the 80lb injectors and HPX (SCT actually) MAF, everything else is stock. It starts and runs fine, but I wanted to get the IAT working properly before working on fuel trims. That will be a subject for another thread. I think I've got the resting resistance correct for the ECU to read the proper iat value, I'm just not sure how will be the best way to verify sensor output at higher temps, etc.

I want to use this MAF because I'm familiar with it from my work on Fords and I had one on hand so I figured why not? I don't mind the challenge as long as there is a solution.