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Discussion Starter · #1 ·
I have a 2004 Subaru sti. Built motor with iag stage 2.5 block +1 valves stock cams, 20g turbo, Cobb 1050cc, 93 tuned, Fmic, tial bov, Tvg delete, EWG, aem x series afr gauge. I have a problem that my tuner has been trying to help me figure out, was trying to see if anyone else has ever had this problem. The AFR on the Cobb AP is very erratic and jumpy where as in the aem gauge it’s smooth and acting normally. I’ve tried multiple things to fix it and nothing makes a difference. Replaced aem x series gauge, replaced ecu, cleaned all grounds, added grounds. I have switched the wire for data logging from the rear o2 to the tgv and problem didn’t change. Checked alternator for rippling but was good. Not sure if something is back feeding into the sensors or if there is a missing ground. And the series x is wired up correctly as far as I believe for data logging. Even when tuner put max smoothing on it is still very erratic and jumpy. And help would be greatly appreciated thanks.
 

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The AP is not able to accuratly read AFR. It basically only able show a short term fuel trim. Bascially it can only show a quick/active AFR over the course of an instance to keep it in laymens terms. Thus, "short term fuel trim" To accuratly get a proper AFR reading you will need a wideband set up, which you already have. Thus why your wideband gauge is showing to be more accurate than the AP readings. Its showing you a true AFR reading over a wider spectrum and not just a quick calculation.
 

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Discussion Starter · #4 ·
@yamahaSHO i have I followed the voltage from the controller to the ecu where it goes in, I put multimeter near ecu and another one near the wideband controller and watched voltage, the voltages are smooth and not jumping. I would post a video on here to show but idk how to do that :/
 

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Looked at your log and videos. I would take another log and add battery voltage to it. Looking at the AP video, the battery voltage seems to have a lot of fluctuation, as well as it seems a bit low.

For the two multimeters, is one on the WBO2, 0-5v output and the other on the wire going into the ECU?
 

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Discussion Starter · #9 ·
@yamahaSHO yes one wire at the ecu and others wideband. And yes the battery is erratic as we’ll the reading on the ap for the battery isn’t accurate. The car is charging 14.3. I’m guess it’s a sensor ground causing the issue but not sure how to go about it.
 
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