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Old 12-23-2019, 12:28 PM   #1
Louisvillewagonmafia
Scooby Newbie
 
Member#: 348886
Join Date: Mar 2013
Chapter/Region: MWSOC
Location: Louisville, KY
Vehicle:
2004 Subaru FXT
Red

Default Logging WBO2 Via Rear O2 Voltage

Hello all

I am attempting to log a 0-5 Volt analog output from a UEGO gauge via my AP using the parameter "AF Sensor 3 Voltage". Rather than getting 0-5 volts, i am getting about 0.8-3.5 volts in my log, and find that the voltage is inverse to what it should be (i.e. high afr reads low voltage, low afr reads high voltage).

When i invert the voltages that i get, and then scale them, i get a response graph that follows the slope changes of the primary AFR readings, so i know it is reacting appropriately, but it seems the parameter that i am using to log is perhaps interpreting the data incorrectly at import from the ECU.

COBBs monitor lists suggests that there is a "direct" version of this parameter that can be logged which has a true 0-5 volt range and higher resolution, but i do not see it in my log list as an available option and cant dig into creating new log parameters in ATR like i can in an OS suite.

The vehicle is a 2009 forester XT- I would have just used the cobb custom sensor logging for this, but it is a CCF feature which is unavailable on the 2009 FXT platform. I am trying to avoid hooking up a serial connector and an in-cabin laptop if possible, and had hoped that pulling voltage over the rear O2 line and converting in excel would suffice instead for my OL tuning.

has anyone ever run into this before? if so, how did you manage to reconcile the voltage readings, or otherwise condition them? I had considered re-calibrating my AFR gauge for an analogue output which models a non-linear nernst cell instead (0-1 output range, inverse relationship)- but wanted to reach out for other thoughts first.

thanks all
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Old 01-03-2020, 10:07 AM   #2
Louisvillewagonmafia
Scooby Newbie
 
Member#: 348886
Join Date: Mar 2013
Chapter/Region: MWSOC
Location: Louisville, KY
Vehicle:
2004 Subaru FXT
Red

Default

At the expense of exposing my brain fart here, It turns out that my problems were twofold- first, i had a bunch of wires in the same area and accidentally tapped my boost gauge signal wire rather than my AFR signal wire, resulting in a correlated but inverse signal being logged (moving too fast!) and second, i had grounded the early version of the UEGO gauge, which has a common power and signal ground, through the rear-O2 harness ground. Because this is an ECU sensor ground location, grounding the combined power/sensor ground from the UEGO to an ECU ground with PWM signals was a no-no and produced voltage spikes and off-readings. For this particular gauge, the non-X series with the common ground, a much cleaner signal comes straight from the battery ground instead.

to note, if you were using the X-series gauge, then the black ground would go to the battery (or chassis, as it is only power) and indeed the best ground location for the brown sensor-only ground would have been straight to the ECU via the available Rear O2 harness for the best analog voltage readings. The feedback issue only occurs when the UEGO ground is a common sensor/power ground.
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