Connect GM IAT with AFM in place
 

Hi,

for the parallel installation of the MS1 in my 99 NB I made myself a little wiring plan - one thing which I am still not sure off is - how do I wire the GM AIT sensor - if I understand it right - one sensor wire goes to pin 20 at the DB37 - where goes the other wire (because I still need my AFM - to keep the car from throwing CELs). Can I connect it to pin 26 - Vref as this applies +5V? Or do I need a different voltage?

Thanks

Sven

Ground (earth).

The IAT sensor is a variable resistor. One wire goes to pin 20 where there is an internal pullup, and the other side goes to ground. Pull a wire back to the MS and ground it to the common point, which means the point at which the MS and its other peripherals also go to ground.

When doing that your IAT sensor this way(wired directly to MS) bias resistance in Easytherm has to be set to 2490.

Uhm, yeah. Since R4 is 2.49k, what other value would you ever set in EasyTherm for a GM IAT sensor?

1450 when sharing it with a 90-93 ecu :)

As I have a preassembled 3.57 board with the R7 installed - which value would I take? 790? ( I don't really want to solder on the board - or do I have to?)

Greets

The bias resistor's value is 2490 ohms.

I said "...for a GM IAT sensor", smartarse. Not gonna be sharing that with a '90-'93 ECU, are you? :nuts:

Since you are doing a parallel install, if you plan to share either the CLT or MAT sensor with the stock ECU, you should remove the corresponding pullup resistor, and enter the bias value of the pullup from the stock ECU, which Braineack has listed in his writeup for various years.

Alternately, you could install a separate GM-type sensor for the MS. This will simplify your build and your future software configuration.

I did of course refering to the clt sensor, which I am going to share. Is it possible to use the value of 790 like Braineack suggests for a parallel install with R7 in place?

If one is doing a parallel install, as the OP is doing, and wiring the GM IAT sensor through the factory wiring he/she has to take into account the resistor in the stock ecu. Just making it clear to the OP that he does not have to do this if he wires the GM IAT directly to the MS. I'm sure some people might overlook that when doing it that way.

No, because you have no way of editing the bias resistor value programmed into the stock ecu to take into account the presence of the R7 resistor so the stock ecu will not know your correct CLT and will not turn the fans on at the proper time. The stock ecu also uses temp for idle control. I guess if you give fan and idle control over to the MS you can do it that way.

what you should do for your 99 is leave the MAF connected and plumbed. Then simply wire the GM AIT directly to your MS harness. Ground the other lead.

I agree as Joe stated in post 2.

That is what I am going to do... but then again - I will have to remove the R7 of the MS board due to the fact Paul brought up - that otherwise my fans won`t turn on?!

Greets

Or just install another GM type sensor just for the MS, just like what you are doing for the IAT sensor.