Stoich/IFR Scaling Potential Long Term Issue

As we know, the IVT calculations go out of whack when you scale the stoich/IFR (to get around the IFR limitation). I can't wonder if there are long term consequences of doing this, such as potentially killing the O2 sensors.

So has anyone done this long term to see what may happen, other than me? I have a bone stock '08 C6 A6. I took the stock file and doubled stoich and halved my IFR, then adjusted the fuel scalar (for my DIC calculations). After many months of running it like this (and over 10k miles - I drive the car over 800 miles a week for school), my car stated idling funny at times, and became progressively worse. I scanned and found that my O2s were bombing out, but NO codes whatsoever (odd). STFTs and LTFTs would be severe negative (-25% and -20% respectively). The funny idle quirk was them resetting back to 0 every 15 or so seconds. I put the stock tune back in and exact same thing, which told me more than likely the O2s were toast. I installed two brand new factory ones and now they are within +/- 3% at all areas.

But here's the kicker, the car was still getting normal economy even with the old O2s like this. I was averaging 28-31mpg before the new O2s and the same after the new O2s. The only difference is that my fuel trims are normal again. Apparently there was some sort of learning going on.

Thoughts?

There is a potential difference that the pump shot gets all out of whack. This can actually affect the driveability AND fuel consumption greatly. Although in the end, its one giant multiplication table to arrive to the final injector pulsewidth, there will be some instances where the size of the injector x commanded AFR will play a bigger role and the dynamic fueling is it. I honestly don't know (doubt anyone actually does) the exact equation for the dynamic fueling, but in essence it could be calculating the extra fuel as a function of a smaller injector without taking into account the desired or commanded AFR. Extra fuel is just that, extra fuel and not necessarily referenced as a function of AFR. Although the commanded is the commanded AFR and the ECU must follow that, I know that the dynamics is a multiplier of the MAF g/s. So go figure.

Now we don't know how its calculated and there is NO pid that we can log to see how much dynamic fuel is being injected... But it would be interesting too see... The only thing that will kill Spark Plugs and O2s is Lead and excessive fuel.

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Originally Posted by yellz06

BTW.. you were getting 28s with the old o2s and 34 with the new o2s.. now.... don't be shy.

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LOL! I can't 100% say that yet because my DIC shows 28 today. The day I tested new O2s I was driving from 6200' elevation to 5200'. After driving back up I then was around 28-30.

Which, with the fuel trims negatives should have had less consumption though... weird. Guess the lack of power to a degree does affect fuel consumption too.

I've been doing this for years on multiple vehicles including my own. Not a single vehicle has trashed a set of O2s.

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Originally Posted by DSteck

I've been doing this for years on multiple vehicles including my own. Not a single vehicle has trashed a set of O2s.

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Thanks for your input! What are you doing with the IVT table, just scaling the values as far as able? I haven't peered far enough, but I assume it's the axis that is going off by 50% (whatever value the IFR is scaled by)?

I'll redo this long term test over the next few months to see if these new ones stay stable. Hopefully there was just something else amiss instead.

I push values over slightly. I've requested HPT to give access to the IVT calculation coefficients because apparently AFR is just a straight value (no AFR^2 coefficient in the model).

The IVT ends up artificially higher. As far as adjusting, YMMV.