Bank 2 STFT goes rich without Bank 2 O2 command

[randallrocket]

So I'm struggling with this issue as I want to keep the O2s on for STFT. I have a 6.0 with a turbo, 3 bar SD p01 on pump gas. I've been running with the O2s on for years and suddenly bank 2 O2 shows pig rich starts pulling fuel from STFT bank 2 which makes it go way lean. I tried everything, new O2 sensors, swapped bank 1 and bank 2 harness plugs. I moved Bank 2 O2 to several locations with varying results. To try and track this down I splint the harness on bank 1 O2 plugged both bank 1 and bank 2 into the one sensor. Now both B1 O2 and B2 O2 read the same and everything was looking great but after 15 miles of driving the Bank 2 STFT starts adding fuel up to 20% while both O2s are the same. If I shut the O2s back off everything looks normal.Screenshot (2).png attached is a screen shot of the scan showing bank 2 STFT going rich. Any help would be great. Also this is a 04 Colorado 6.0 4l80e gen 2 78/75 turbo, it weights 4100lbs. Best time so far is 9.91 136 mph.

[kevin87turbot]

So I'm struggling with this issue as I want to keep the O2s on for STFT. I have a 6.0 with a turbo, 3 bar SD p01 on pump gas. I've been running with the O2s on for years and suddenly bank 2 O2 shows pig rich starts pulling fuel from STFT bank 2 which makes it go way lean. I tried everything, new O2 sensors, swapped bank 1 and bank 2 harness plugs. I moved Bank 2 O2 to several locations with varying results. To try and track this down I splint the harness on bank 1 O2 plugged both bank 1 and bank 2 into the one sensor. Now both B1 O2 and B2 O2 read the same and everything was looking great but after 15 miles of driving the Bank 2 STFT starts adding fuel up to 20% while both O2s are the same. If I shut the O2s back off everything looks normal.Screenshot (2).png attached is a screen shot of the scan showing bank 2 STFT going rich. Any help would be great. Also this is a 04 Colorado 6.0 4l80e gen 2 78/75 turbo, it weights 4100lbs. Best time so far is 9.91 136 mph.

That's an odd issue...especially since you have both O2 sensors reading the same value. That eliminates the O2 sensors and the wiring. Do you have the same switching values in both Bank 1 and Bank 2 tables?

[randallrocket]

Yes they have the same values. I know this is weird, that's why I'm on here.

[Hondaeater]

So I'm struggling with this issue as I want to keep the O2s on for STFT. I have a 6.0 with a turbo, 3 bar SD p01 on pump gas. I've been running with the O2s on for years and suddenly bank 2 O2 shows pig rich starts pulling fuel from STFT bank 2 which makes it go way lean. I tried everything, new O2 sensors, swapped bank 1 and bank 2 harness plugs. I moved Bank 2 O2 to several locations with varying results. To try and track this down I splint the harness on bank 1 O2 plugged both bank 1 and bank 2 into the one sensor. Now both B1 O2 and B2 O2 read the same and everything was looking great but after 15 miles of driving the Bank 2 STFT starts adding fuel up to 20% while both O2s are the same. If I shut the O2s back off everything looks normal.Screenshot (2).png attached is a screen shot of the scan showing bank 2 STFT going rich. Any help would be great. Also this is a 04 Colorado 6.0 4l80e gen 2 78/75 turbo, it weights 4100lbs. Best time so far is 9.91 136 mph.

If you split harness and plugged both O2 harness wires into B1 sensor and they read the same, now 15 miles later bank 2 is going rich while both o2s are the SAME?, you have issues for sure. Recap: B2 STFT goes rich, pulls fuel and B1 is fine when B1&B2 get the same "feed" to the harness to ECM which IS reporting the same reading as B1? The ECM is.... without the CL feed back from B2, right it shows same as B1 because they are the same...... but B2 rich, STFT pulls fuel but the B2 o2 sensor reading is still stoich SAME as B1. WOW. I have never seen an o2 show normal and the ECM adjust the trims on its own?

Does a WB read the same on both banks? I mean is the fueling correct but ECM is wacked or is the fueling ACTUALLY changing even though B2 sensor reports normal from splice with B1 and ECM is randomly making the STFT adjustments really changing the fueling?

Because both harness wires were getting fed from B1 o2 and it still went STFT rich B2? adding 20% fuel, it is not a sensor or exhaust or fueling issue. There was no B2 in the loop and if it was getting reversion or an exhaust leak, bad injector, both B1&B2 would pick it up because it is the same sensor. Nice diagnostic idea.
I hope you keep us posted.

[randallrocket]

The first time I tried this the WB showed it was adding fuel. Just for the hell of it I changed the injector bank selector to all 0s which is bank 1 O2 feed back only and it shows rich on bank 2 STFT but but does not show on the WB. I did not aba test this. The screen shot I posted shows WB at 15.1 A/F. I don't trust what's going on to leave it like that. I can run this in open loop but I don't want to. My next move with this truck is E85. I have redone the fuel system and installed sep 1500 injectors and tuned for the injectors still on pump gas. I still wonder about the B2 O2 harness if it could be pinched or melted or ?