Confused... STFT's are negative... but WB sensor shows super lean!

[RealQuick]

Hey folks,

Been tuning my 2010 ss m6 with hptuners, and it is pretty cool. Having an issue as of late that I cant figure out.

Mods are Ported LS3 heads, cam (235/231 6xx/6xx 115lsa), LT's, no cats, catback, CAI and recently added a ported stock intake (opened to 102mm) and NW102mm TB. The last 2 mods have introduced driveability issues, and now recently, this new issue in the title.

Simply stated, my ve table was setup using a WB only.Once dialed in, I allowed the stft's to come on to compare to my AFR... and things got wacky. STFT's show negative numbers (so it thinks I am rich), but my WB shows way lean when the STFT's are on.

I attached my idle (with no stft's), then idle with stft's on, then my cruise around with the stft's turned on. I will also attach my tune (work in progress, so don't kill me too bad).

Thanks a bunch, this forum has been helpful in my learning process!

Jon

[RealQuick]

I leaned out my ve tables to see off over fueling tricked my wb, but it showed really lean (~17 afr), and the stft's was adding like 5-6% fuel to pull the AFR to 16.3 where it stabilized (commanded is 14.68)

[schpenxel]

I'd go back to your old TB first and see if that helps. Those wideband readings are all over the place. Something isn't right.. Usually when the wideband goes from greater than stoich to less than stoich you'll see the narrowband O2 readings quickly swing from ~800mv to ~200mv or the opposite. Yours aren't behaving correctly at all..

Are you sure the wideband is setup correctly? Any exhaust leaks?

[RealQuick]

Thanks for the response!

I could have an exhaust leak. I'll check tonight... I am also going to pull the spark plugs tonight and take a peak at them.

[RealQuick]

Just for clarification... the WB O2 is on the driver's side in an off road pipe.

[schpenxel]

Regardless, something isn't right. NB O2's cycling should happen right around stoich on the wideband.. on mine if it's at .98 lambda or so the narrowbands will go high mV, 1.01 or 1.02 lambda and they will go low.. and they line up right on with the WB

[RealQuick]

Update, I may have an exhaust leak before the WB (it would explain why the WB shows lean but the NB O2's upstream are showing rich). The slip fit off road pipe (that my WB is in) slip fits on the outside of the header collector. The clamp that squeezes down the off road pipe onto the collector was not tightened down enough. This means a leak would not come out, rather atmospheric air could siphon in as exhaust pulses flow by. I tightened it down and will fire it up tomorrow. Cross my fingers...

[schpenxel]

Yeah, that would make sense.. Get that fixed and at least you'll get accurate readings, then go from there.

[RealQuick]

Well, WB now reads 15.3 at idle, then turn stft's on and they are ~+3, so it appears to be what the problem was. So WB reads lean, and now the trims are adding fuel! Thanks for the responses!

[schpenxel]

It should be right around 14.7 with fuel trims enabled

[RealQuick]

Yup, the 15.3 was before the trims were enabled. I turned the trims on and it started pulling the AFR down by starting to add 3% fuel (pulling toward 14.8 AFR)... Close enough for me! Thanks again.

[schpenxel]

Gotcha. Sounds good to me!