Hey guys, wanted to start a thread to discuss the possibility of logging wideband AFR using the Rear O2 ADC Input on the factory ECU. It's come up recently that the new *ANALOG* AEM UEGO Wideband AFR gauge (30-5130) lacks a serial output, which for the time being means no logging WB AFR in Evoscan.

However, the Evo 8/9 guys have found a way (via mrfred) to log wideband AFR through the ECU, eliminating the need to bother with Serial cables and Serial-USB adapters. It’s accomplished by adding a patch to the ROM that simulates the Rear O2 signal and then routing the 0-5V ADC signal from your WB AFR sensor to the 0-5V ADC Rear O2 input on the ECU. You then make a new table in Evoscan for Wideband AFR, enter the sensor’s transfer function (AFR as a function of voltage,) and you’re set… in theory.

Here is mrfred’s thread for some background: https://www.evolutionm.net/forums/ec...ial-cable.html

What you'll need:

• Wideband AFR Sensor with 0-5V ADC output
  
  
• Access to an OpenPort 2.0 (Tactrix) cable to disable the Rear O2 sensor in EcuFlash

Still to come:

• O2 Simulator Patch (in the works for the Evo 10, eliminates CEL when Rear O2 is removed)
  
  
• ECU pins (Evo 8/9 ECU pins are available online/Jack_of_Trades, but not sure if either will work for the Evo 10… my guess is no, but I still have to take a look at the pins)

So, Gurus, disassemblers,… is there anything else that needs to happen to get this working? And is an O2 simulator patch something that could be figured out in the near future? I'm willing to devote some time to getting this to work, if anyone else is interested, it would be great to have this available for the Evo 10 community.

All input welcome.

 

Tephra has said that once you disable the rear O2 sensor by toggling bit.1 of ECU Options #2, you can add your analog output (+) into the yellow wire of the rear O2 harness. EvoScan is already setup to log this (LC1 AFR or something, I'm on my phone).

You'll need to adjust the formula in EvoScan for the gauge, so please post the voltage:AFR values from the manual here and we can tell you what the new eval will be.

Since there isn't yet an O2 simulator patch, you'll likely still get an O2 related CEL, but hopefully that is taken care of soon !

Oh, another thing. You need to remove your rear sensor when you disable it. When you disable it, the heater is also disabled and if it is still in the exhaust stream, it will get damaged.

 

Thanks for the reply, hopefully the O2 simulator patch will appear sometime soon, I was hoping to leave the rear O2 is place, but oh well.

And for the eval function, can I throw the V:AFR values into Excel and then curve fit for the equation?

If I can get my WB bung in this week, I should have a first attempt (Posi-tap ) at this made by the weekend, very exciting.

 

just like in CT9A the Pbit sometimes doesn't work...

it works for me, but not for you guys apparently

anyways, the rear02 connector under the passanger seat is what you need to tap into, just tap the yellow wire (bottom right pin on the D35 connector going back to the car)

I plan to do the rear02 sim soonish, but got a lot on atm

 

Whenever you get around to it, you'll make lots of people happy. You're already my tuning hero for the amount of work you've put into the X

 

And yes, that's exactly what you need to do for the Eval. There is a good chance it is linear anyway, what does it say in the documentation?

 

I'm not familiar with what the Pbit is/does... Is this the bit we toggle to disable the Rear O2?

So, USDM does NOT have Rear O2 disable through EcuFlash yet? I need to pay better attention sometimes...

+1

It is in fact linear; I totally forgot that there is a table of AFR vs. V and the transfer function in the documentation. The TF provided for mine is 2.375*V + 7.3125. And for the eval do I need to divide the TF by 255?

 

Oh, and thanks for this.

And can I just Posi-tap into that wire or do I need to strip and solder?

 

positap should be ok - its not a high current wire.

just as long as you got a good connection

try the rear02 disable bit - (also disconnect the D35 connector) you might find it works just fine

 

Thanks Dave, I'll report back on whether it works or not.

And for my eval, do I need to divide the transfer function for my gauge by 255 or do I leave it as is?

 

post up the 0v AFR and 5v AFR and I wil let u know the formula

 

0.5 V at 8.5:1 AFR
4.5 V at 18.0:1 AFR

In the documentation the transfer function for the output is listed as:

AFR = 2.375*V + 7.3125

Thanks.

 

ok so to get the ADC into voltage its:

V = 5 * ADC / 1023

So your final formula will be:

AFR = 2.375 * (5 * ADC / 1023) + 7.3125

What ROMID are you - I will tell you what your ADC memory address is for the rear02 so you can put it all in evoscan

 

I'm out of town at the moment without my car, but I'm pretty sure it 52680020.

Thanks for the help Dave!

 

0x80834E - it's 2byte

Let me know if you need anymore help