intenseapple

I've been pestered by this issue for quite a while now and cannot figure it out. I have a turbocharged 1995 running an MSLabs MS3 basic. Everything works fine other than the IAT input, which reads a consistent 70*F AKA not connected. I have the sensor wired directly to the MS wire harness, not using the stock harness, to the 2P and 2F pins on the ECU connector. Polarity shouldn't matter and I have tested and confirmed continuity for both wires between the sensor pigtail and the wires right before the ECU connector. Is there a jumper or other internal MS issue that could cause this, or is there some component in the stock wiring harness that I am missing? The only thing I can think of is that the pullup for the circuit is in the stock harness and not in the actual ECU as I thought, is this the case?

intenseapple

BUMP. Did more poking around and still couldn't find any issues. ECU looks perfectly fine, no noticeable burn marks or loose solder. Next step is to try to wire up a 2490k pullup for that input and see if that gets me anywhere, any other ideas?

Spaceman Spiff

Have you verified the sensor is working? Should just be a thermistor if memory serves, measure the resistance across the leads with a DMM at room temp and then a minute or two after you dunk it in some boiling water. Could be the resistance value is out of range as far as the MS is concerned (e.g. there is continuity between sensor leads but the thermistor is just shorting). Easier to verify that first before you go digging around in your MS (which you should really consult Rev on first in terms of troubleshooting steps).

intenseapple

Fair point, and yes it is just a thermistor. I've actually got a new sensor in the mail right now to rule that out, although I haven't actually tested the old one. It will be great if a new sensor is all I need.

SpartanSV

What documentation shows 2P and 2F?

intenseapple

This link that I have had saved for a while as well as wiring diagrams for my year. Both indicate that those pins are where the stock AFM IAT sensor wires go to.

SpartanSV

Look at your link and tell me what it says 2F is. Looks unused to me.

2P is correct AFAIK for one of the wires from the sensor. The other wire should go to sensor ground. Try 2D.

intenseapple

I'll give it a try and report back. This link is where I found the wiring diagram. I traced both temp sensor wires back from the AFM to the ECU and ended up with those two pins, I assumed that using the same pins as the stock AFM would work fine since most MS install instructions reference using those two wires at the AFM connector for the GM IAT sensor.

Reverant

iTrader: (10)

2P is correct, however 2F is incorrect as SpartanSV said. Connect it to 2C or 2D.

intenseapple

Thanks Spartan and Rev! I got the sensor reading properly. I way overcomplicated things and simply rewired 2F wire to sensor ground and forget about it.