Originally Posted by
gmtech16450yz
Thanks 10_SS! You saved me a bunch of typing! And no, that absolutely wasn't a stupid question jtrosky, it was actually an excellent question.
As 10_SS stated, narrowbands do a very good job of keeping the mixture at stoich by switching back and forth between too rich and too lean. There is another big reason that most manufacturers have stayed with narrowbands, and that's the catalyst operation. A 3-way cat NEEDS the mixture to be both too rich AND too lean, that's how it operates. The very short explanation is that if what's going into the converter was perfect combustion, it wouldn't have the elements needed to control NOx. So since the cat needs the mixtures to swing back and forth between too rich and too lean, a switching oxygen sensor works great for that.
And yes, some cars already have widebands from the factory. The Bosch E69 used in the GM Ecotecs like the LNF have factory widebands. Not only that, they run in closed loop at all times, even during WOT. If LS engines had closed loop WOT fuel control there would probably be half of the blown engines that there are now. When you do a mod that makes a constant closed loop engine too lean, it doesn't blow up because even at WOT it knows it's lean and richens the mixture automatically. (In general terms obviously.) The fuel control in a Direct Injected Bosch E69 LNF is amazingly accurate. It makes tuning an LS engine seem caveman crude in comparison. LTFT's are normally within -5 to +5%, even from the factory. I usually shut off LTFT's because STFT's are plenty enough control in those engines, and even those can be tuned to stay within a -10 to +10% span. Watching commanded and actual Lambda in the logs, they're almost always exactly the same. Oh and they use Lambda in those ECM's too, none of this AFR or EQ Ratio stuff. lol.