Question on VE Tuning with AFR Error

[BuckNasty92]

So recently I?ve been wanting to do some refinement of my VE Table. When I first installed my cam, I wasn?t comfortable enough to do my own tuning yet so I had it done by a reputable local tuner. That was a few years ago and I feel more comfortable using the software now and I would like to refine my VE table a little more. The tuner told me that the wideband in my pick up was off by .20 in comparison to his (tube up the exhaust). With that being said wouldn?t using the AFR error method produce a tune that?s actually off by .20? Would like to do this but this thought has me holding off. Wideband is in the exhaust 8-10 inches back from collector on driverside and is an AEM 30-4110.

[Jeff7577]

Your wideband is probably more accurate than his sniffer. When you go up the tailpipe even the smallest of leak in the piping will draw oxygen and throw off the reading. You can test your error by looking at your closed loop trims, commanded afr/lambda, and actual afr/lambda.

If you are cruising with LTFT at 0, commanded lambda at 1 and actual reading of 1.02 then its safe to assume your wideband is reading lean. Not at the same time obviously as it will be switch around stoich in closed loop.

The first time I used my LM-2 with the tailpipe adapter I did the VE table with the wideband and when I went back into closed loop it was not accurate enough due to the tailpipe location. I ended up doing VE with fuel trims which works very well, and then calculating the approximate error introduced to my wideband and did 4000+ with it. Once I calculated my wideband error using closed loop trims it was accurate.

[BuckNasty92]

Thanks for the reply Jeff. In my head I thought that mine would be more accurate for what you stated with every small leak. Currently I have LTFT’s disabled in my tune but I’d like to enable them again since it offers more data for how my truck is running. Although it is cammed and stalled, it gets pretty terrible fuel mileage considering, even when converter is locked in overdrive with 3.73 gears and is why I’d like to revisit the tune now.

This is the first time hearing of using fuel trims to tune VE but I’d like to learn more on it. Do you happen to have a link to a good write up or some personal tips?