Connecting the same IAT sending unit to Gauge and ECU

[jayrex]

I am not that great with electrical, hoping somebody can confirm or deny this setup as possible.

 

I have a Dual Intake Air Temperature gauge hooked up. I am looking to try out a Speed Density Tune so I'd like to use the sensor which is already located just before the Throttle Body(FMIC Piping). I would like to read the gauge and send that temperature data to the ECU at the same time, without having to weld in another bung for a separate sending unit. I am wondering if I can connect both the gauge and the stock IAT wires at the same time, or does that somehow invalidate the voltage/resistance reading.

 

So basically a Y connection from the sending unit.

[Notorious]

Theoretically it will be fine, the voltage readout will be the same but I would worry about inconsistencies. I would wire it up to the stock IAT for the tune and once it’s done, move it back to the gauge.

[awfulwaffle]

Been a minute since I've done any EE work in a professional setting, but here goes:

 

I'd start by taking an impedance/resistance (should be effectively the same in this case) measurement of the ECU input pins, the IAT sensor and then the input pins on your gauge.

 

As long as your gauge has a much higher input impedance than the IAT sender's internal impedance, I think you'll be OK. If not, you could make a simple isolation amplifier for less than a buck using Digikey or Mouser parts. Check here for an intro: http://www.learningaboutelectronics.com/Articles/Isolation-amplifier

 

If the input impedance of your gauge is much higher than the ECU inputs, you may introduce some high frequency noise but I'd think the ECU inputs are filtered so it's probably OK. Log some IAT values after you get set up to make sure they're not jumpier than before.

 

Make sure you're only applying excitation voltage from one source. That is, power the IAT sensor using existing ECU power and don't use any of the supply leads from your gauge.

[jayrex]

Awesome thats what I needed to know. I was just hoping someone wasn't like, "Nope. Won't work"

 

I will definitely try them separate and combined to compare the logs.

 

Thanks for the info!

[awfulwaffle]

One more thing to note: if the output voltage range on the IAT sensor doesn't match the input requirements on your gauge, you could add a little gain to that isolation amp to match, assuming there's no offset.