2013 Sierra Denali 1500 6.2L Truck is dead stock at the moment besides a muffler. Disabled COT, DFCO, MAF, PE. Was trying to dial in the VVE table using VVE vs LTFT as I was seeing some 10% LTFT's. I have the secondary O2s shut off and a Wide Band installed in B1S2, B1S1 hego seemed super lazy so I replaced with brand new NTK sensors and it was a touch better but for some reason I keep losing STFT & LTFT on Bank 1. Not sure if I have another underlying issue with an exhaust leak or Vac leak but so far smoked everything and sprayed around intake with brakleen and no audible exhaust leaks or issues found. Once Bank 1 trims fail they won't return unless I shut truck off and re start, as you can see later on in the log Hego 1 shows lean and Wideband is still reporting well. Also has new plugs and wires. Pick er a part boys!
Tune your VVE with AFR error, not LTFT, if you are running a WB. My understanding is LTFT hang on to 'trash', so if you're going to use trims, disable LTFT and tune off STFT. scanner.jpg
B1S2 is post cat- it needs to be pre main cat, within 18" of the collector IIRC. You have precats directly off the manifold, so you'd either need to replace a NB with the WB or add a bung near the NB, but before the main cat under the passenger seat.
Did it do the same thing before installing the wideband? Sounds like it could be a bad connection, short or broken/partially broken wire?
I always ran my WBO2 separate from the NBs since I had LT's and ORY on my last truck, but I'm now in the same situation as you and plan to just add a bung.
If everything is stock and you have fuel trim issues you may want to address them before modification. Something as simple as having the flex fuel % incorrect for actual content could easily be the issue. I have reset many times to correct issues. If you want I can walk you through testing your fuel for ethanol. Pretty easy actually. It is one of the first tests I do as a diagnostic for driveability fuel mileage and MIL issues on vehicles equipped for E85 due to having many E85 stations here in SoCal.
Thanks for the reply guys, I realize the WB should in theory be pre cat but the industry worked off tail pipe sniffers a whole bunch and from my understanding failing the post cat sensors and using that bung should have very little effect with the cats still installed. Not confirmed though and I haven't done any testing pre and post cat yet, I'll def install a proper O2 bung pre cat as soon as I get headers and catted Y pipe in the future when I do the cam swap. Just getting the hang of dialing this thing in and navigating the scanner and editor.
I absolutely was wondering why use the LTFT especially for part throttle and figured it would be way easier and more accurate to use STFT or AFR error, Thanks for clarifying that.
I stopped the tuning process atm and have come to the conclusion there is a mechanical problem, Going to yank the plugs (which are new) and perform a leak down. Remove Intake Manifold and install new gaskets then smoke intake and exhaust system. I also noticed a slight mis fire while holding free rev at 1500rpm and can hear it popping out of the exhaust slightly. Confirmed on VCM Scanner with history mis fire and cylinder 6 received 30 mis fires within 30 seconds of free rev. Strange that cylinder 6 is on pass bank and bank 1 is on driver side, also received a couple mis fire history on cyl 1 and 7 but were very small like 2. Guess running mates maybe can skew these numbers ?
I have kept an eye on fuel ethanol percentage in the scanner and iirc these are virtual with no sensor actually installed ? Haven't seen it go over 9% content and last tank it sat around 0% but I do remember reading something about flex fuel content causing an issue. Would def be interested in learning more about it.
Any Idea why it won't let me load a log file, is there a certain size cap on logs ?
If you're doing plugs, do the wires too. They'll need it. To eliminate the coil, move it to another cylinder and see if the misfire follows.
The virtual sensor works great if you aren't tuning. I had a PCM that went bad with the virtual sensor and a write entire of the original stock tune couldn't fix it. It would drift to 60% alcohol after every fill of clear, and drift to 40% after fills of e85. Ended up going with a physical alcohol sensor from Dave Steck at DSX Tuning (who's a huge resource on this forum), and am installing it on a second truck. That and my AEM Uego were the 2 best purchases for tuning.
Got it sorted guys! So I had B1S2 still plugged in and zip tied up under the truck with the wide band installed in its bung and B2S2 still installed in the exhaust stream. I figured once disabling the rear o2s I should be able to carry on with dialing in PT and WOT. I noticed B1S2 was still reporting 0.005 mv (Lean) and B2S2 was also reporting 0.7xx mv (rich). Once I unplugged both secondary o2s it reported 0.450mv (stoich) to the PCM and all was happy. I was then able to dial in the fuel accordingly, with that being said and from what I've read the secondary o2 sensors actually have a minor part in fuel trims for cat efficiency. So not sure what regular practice is, leave them plugged in or removed completely and unplugged and of course some use defoulers. Thanks again for the advise fellas!
S2's do have a minor amount of fuel trim. some of its purpose is to diag front O2's based on the same conditions as cat efficiency and that is cross counts, switch rate or rate of climb and peak to peak voltage for OBD2 rate of deterioration thresholds.
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