We installed a 118 lobe separation Comp Cam, I dunno or care the rest. Long tubes with aftermarket cats and factory on back exhaust. Cold air intake and fire up. Neural network in tact because why make life hard for myself? Also could never get idle to chop or behave with NN off. Odd but so be it. Trans got tuned, nice shifts in drive, paddle and manual. Then the trans tuning book comes out, I've hardly really looked at it yet. I'll get to it. Engine tuned, runs like a champ, tuned PID by means of the method described in the popular posting here. Pretty tight idle in park and drive, etc...

Customer needs to pass emissions, ok, it originally came in with long tubes and a p0430, and o2 slow response for opposite bank. Remove check from MIL but not SES enable. Translates to run test, if fail, don't throw a code, but keep trying. That's what I understand. Seems to work. Could not get the Catalysts to become ready. I found that Multiplying O2 Transport Delay by 2.3 seemed to work the best at getting Catalyst to become ready without the car throwing a fit. Flash, drive 30-40mph, 1300 to 1900rpm, try to keep in that range for 2 minutes. Should be good. And it was.

Car checked out fine. Sent home.

Car back 2 days later. Can't idle, stalls, as if no proper tune in it at all. Logged, +32 long terms on one bank -16 on the other. Closer look shows 0.005 volts on both downstream o2s. What! Looked at plugs, all black and carboned up as can be, cleaned, put back in. Cleared adaptive, car doesn't appreciate that gesture at all. Saw CL- Fault on fuel system status on one bank, then momentarily later the other bank became the same. Frustrated.

Slept on the issue. Came in, disabled both down stream o2s. Cleared adaptives, Car perfectly fine. Drove around. Life is good. Idles and everything well. Still logging downstream o2 voltages, bank 1 appeared to be just fine so I reenabled its downstream. Drove some more. Just fine, No fuel system status faults on either bank. Then, enable the 2/2 oxygen sensor with a flash. Ran the car. That bank fuel system status hit a fault first. Then the other bank got the same fault too. The terrible engine behavior returned. Not good. I googled last evening to see if anyone else had experienced these issues too with no result. Tried different search terms to no avail. Got generic responses from google and rejected them mentally at first but since it was all I was given I decided to try to understand it. And I do now.

I will explain as I understand. What happens is when a bank experiences a closed or open loop fault, the car obviously starts running poorly. Then even worse with the other bank does the same. The PCM wants to equalize the fueling to both banks in normal mode and fault mode. The issue in one bank can migrate to the other bank! I saw it in logs! So disable the downstream 2/2 again, clear adaptives, all is well. Ordered a new 2/2 sensor, throw that in and enable all sensors. Life is good.

Care to comment and discuss? Please do!