Sharing Analog Sensors w/ECU

[mpgmike]

Just acquired a UAEFI rev C. Been playing with TunerStudio and scouring the available info (including this forum). I want to control spark, fuel, and a few other things but keep the factory ECU intact. 1995 Jeep Grand Cherokee. I need to share CLT & IAT with the factory ECU. It has its own internal 4.7k pull-up resistor. In this post (https://rusefi.com/forum/viewtopic.php?f=18&t=2263&p=44242&hilit=share+sensor#p44242) mck1117 stated,

"the analog temp inputs have a 2.7k pullup to 5v. You could always wire your coolant sensor to a voltage input instead, which would probably work."

First, I looked at the schematics and could only find R202 & R206 for IAT, and R201 & R205 for CLT -- all 4 are 680k resistors; 2 are pull-up to 5 volts, and 2 are pull-down to ground. I'm not very functional with Kicad, but tried to find the traces to follow (unsuccessfully). Can't find the 2.7k pull-ups!

Secondly, I tried using AUX1 as a IAT input, but TunerStudio gave errors when I tried to use it in the Ignition section. I see the traces from the IAT & CLT inputs go to a bank of resistors, but about the smallest I can work with are 0603, and I can't read anything on them. Please offer some direction.

[AndreyB]

https://rusefi.com/forum/viewtopic.php?f=18&t=2263&p=44242&hilit=share+sensor#p44242 seems to focus on Proteus while uaEFI boards have different pull-up resistor value.

www.xyproblem.info is wondering what are you trying to accomplish? Why do you need to share sensors with anyone?

[mpgmike]

The factory ECU controls more than just fuel and spark. It sends an output to the gauge cluster for the tachometer, works the AC and cruise control, and other things. Ultimately I'm wanting to control spark through 6 GM LS coils, utilize the WBO2 and control fuel. I'll probably want to control the IAC as well. I don't want to have to rewire everything, for one. Two, the Crank & Cam sensors are fed an 8 volt VREF and send out a 5 volt logic signal. I'd have to deal with the VREF issue for these 2 sensors. I want to convert the IAT & CLT inputs to high impedance on the UAEFI and just looking at net voltage.

Also, this lets me work on one segment at a time. I want to fire a single coil like stock, feed it to my distributor, and start there. Next I'll add 5 more coils... and so forth. Oh, and this is my daily driver, so down time is precious.

[AndreyB]

I want to convert the IAT & CLT inputs to high impedance on the UAEFI and just looking at net voltage.

Two issue here
1) we decode thermistors based on calculated resistance, not with voltage lookup. Thus we need to know real pull-up value
2) in order to reduce technical support we are trying to reduce confusion. On official boards we make pull-up values not user configurable just to make the overall system simpler

pretty much while you have a legit use-case to mix standalone with OEM that would require extra effort on our end. In order to move effort to you not us a suggestion would be to use secondary sensors instead of sharing sensors.

[mpgmike]

Thank you for your attention to the matter. I'll reconsider my plan of attack.

[mpgmike]

I did figure out that if I remove the UAEFI pull-up resistors, I can tap the IAT & CTS signals without affecting them. These are the 2 SMT resistors I removed to allow me to do what I wanted to all along:

PcbMod3.png

[Dzikuss111]

Hi. At front sorry for my bad English, it's not my first language.

I Am attempting something similar like you but the reason why ma stock ecu must stay intact is can communication.

So can you support some better pictures of what resistors to remove so i can sher my iat a clt sensors between two ecu's.
And did you have other pullup problems (TPS), or similar ?

[mpgmike]

Here is a close-up of the 2 resistors I removed:

CtsIatRes1.png