Quote:
Originally Posted by jfitzpat
Sorry, I saw this in the email 'best of' today and just had to comment. There are really three main approaches in altering factory tunes:
Newer vehicles are much more likely to have a 'wideband sensor', or a better idea of exactly where they are running in the .7 to 1.3 range. So those factory tunes generally waste less fuel in those cases. Though there is generally still some waste. The most cutting edge is to use wideband closed loop at targets other than 1.0, but that is another subject.
But people here already avoid that case. So, while they will get savings, it won't be as much as my lead footed wife might get with the same change.
If you don't care about the environment, better economy is not all that hard to acheive.
But emissions get terrible and you potentially destroy your CAT. On my development 'road bed' I still simulate the narrow band signal, but 'tighter' than a real narrow band. That is, I collapse the normal S curve of a typical narrow band. If you track O2 sensor voltage with an OBD-II scanner, you will typically see it oscilalte back and forth, rich/lean/rich/lean as it chases stoich (lambda 1.0). These swings are nec. for cat operation (you need some O2 to burn), but they are a little sloppy. So by making my stock ECU chase a tighter signal, measured emissions actually go down (because the cat spends more time at peak efficiency). There is a tiny fuel savings, but it is so small that it is certainly not worth persuing for its own sake.
My point in all this is that there are savings to be had here, but the big Kahuna is off limits unless you don't care about emissions.
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No offense but if it was easy I would have retuned my 3800 98 buick to run lean on the highway, the Emission of NoX increases but the majority of the rest of the exhaust (as found) is cleaner. Since I live in a rural area the levels of NoX my 35-52mpg car emits are likely irrelevant and will just turn into fertalizer. Now if I were in downtown LA I might worry more but evidence shows NoX may not be as much of a bad guy as the US government believes.
I would love to lean out my 010 Cobalt the rest of the way at steady state loads but finding proper tools is not all that easy or reasonably priced.
Not to mention most tools don't do lean.
Heck many Honda cars ran lean including the gen 1 insight and had EXCELLENT emissions. I don't doubt their technique would have been far superior to our pig rich and CAT approach.