Hi, I am tuning my 85 corvette with a APU1 and AEM 30-4110 wideband. I installed long tube headers and complete exhaust. It has very little back pressure. OEM is one O2 sensor, but I installed a sensor bung 2" after each collector. I have the narrow band in one and the wide band in the other. I am new to tuning and am taking it slow trying out all the features of the APU1 and wide band O2. The wide band seems to be working and giving me good readings.

In open loop, the AFR is is reading 13 -14, and I can tweak the MAF tables to keep it right around 14.5. My problem is closed loop goes completely rich and after a short drive will peg the AFR at 10, with the engine running poorly. Data logging shows the narrow band at 250-300 (mv?), and the monitor indicates "lean", which is obvious because it's commanding a rich condition to compensate.

I swapped the wide band over to that side and it functioned exactly the same in open loop as it did on the other side, so I don't think I have an air leak over there tricking the narrow band.

The O2 sensor is old and I am thinking it is bad.

Does anyone have experience with a longer distance from exhaust port to sensor not giving enough heat for the sensor to function? Is this an issue?

I can get a new sensor for under $20 from rockauto, but I hate throwing money at problems without really understanding the cause.

Thanks