Very interesting this topic came up!. I am in the exact same boat and have been plagued with this issue for quite some time.
Check it out - Long read but worth while.
I started of with an Aerofoce WB Sensor Add on so I could read the A/F on my Aeroforce gauge. Never had any issues with it on the stock exhaust. O2 Bung was welded just a few inches away from the factory o2.
I later decided after I got the ARH LT Headers that I wanted a Dual Pod so I could run a dedicated A/F Gauge like the AEM and retire (sale) my Aeroforce WB Sensor kit. I bought one on here used and it worked great for a month or so. I had the WB installed in the factory 02 Bung that ARH installs in their midpipe (typically for the Secondary 02's) The weather started getting cooler here which is about the only thing I can really put my finger on that changed recently and out of the blue one day on my way into the office the AEM suddenly went to FULL LEAN 19.8 and would spastically read the correct A/F for a brief second or two here and there. Nothing I could do to ever get it to read correctly like it used too..
I called AEM and they convinced me to ship my gauge in for them to run a diagnostic which I did but I also decided to purchase a brand new unit while they evaluated the used one. Since the Signal and power harness was the same as the one I already installed I just swapped out the Gauge and was disappointed to see it was still not working. The moment I swapped out the BOSCH Sensor it started working fine for about a day and then went back to being mostly stuck on lean 19.8. Ughh!
I called the place I bought the new unit from and they agreed to treat it as a defective unit and shipped me a brand new one. So 2nd brand new AEM kit. This time I swapped out everything. WB Harness and Power harness. Soldered every connection and wired the power source to come on with the "KEY ON" as it was recommended by some friends who have theirs wired that way without issue.
This one lasted about a week and a half and went bad.
Now I was fed up with this and decided to Return the AEM Kit back for refund and just purchase another WB Sensor kit from Aeroforce (Since I sold my original one).
I got the Aeroforce wired in and after a bout 2 weeks it started reading lean but not quite as bad as the AEM and would still read WOT A/F.
Fast forward to today:
I spoke to my tuner Ted Jannetty about the issue and his theory is this: The WB sensor being located a good bit away in the midpipe, plus the fact that its heating up the moment I hit the start button (which is not starting the car yet. Just moving my seat foward, taking the M6 out of gear, etc. WHen I fire up the engine the Sensor is getting Shocked with the condensation / Water and killing it. Maybe this wasn't a problem during the warmer months. He said to try putting in an inline switch and only turn the sensor on after the car is thoroughly warmed up.
So I bought another WB Sensor but this time I did not buy a BOSH one. The one I got specifically said this about it:
[Performance】The metal shroud does not look as shiny as other Oxygen Sensors. Because it is made of SUS310 high temperature resistant material. And every single item is heated at 1562℉. The high temperature also makes it stand wear and tear.
Link to product:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
They have a no hassle Return policy on the Sensor for 1 year. That right there is something AEM wouldn't even honor. They told me a week old kit with a bad sensor is NOT eligible for warranty.
In addition I am no longer using the secondary o2 bung in the midpipe. I had an exhaust shop weld in a new 02 bung into the headerpipe collector so it's much closer now instead of being so far back.
I changed the wiring so that my 12 volt source only happens after the engine is started and to go above and beyond I have a timing circuit I made that waits one full minute before it powers the WB 02 up. I didn't want to have to flip a toggle and forget to turn it off, etc. So far the timing circuit works like a charm.
So far I've had this for a couple days so we'll see if it holds up. If this sensor fails too then man I give up!
Sorry for being so long. Hope this helps.
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