jfitzpat -
Quote:
Originally Posted by jfitzpat
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Actually, they run at stoich a lot. As much as possible. Again, you can tell by looking at the O2 sensor. The narrow band sensor detects a very narrow range around stoich. It is very accurate at finding stoich because the chemistry actually reverses as it is crossed. If the O2 sensor is oscillating, the ECU is 'chasing it', and you are there. If it is reading high, you are enrichened, usually under fairly aggressive accelleration (when you kick the ECU into "Open Loop"). When it is low, you are lean, typically in coasting and recirc situatations.
It HAS to hit stoich a lot for the CAT to function at all. Cat efficiency plummets as you move off stoich. This is because the high EGT is needed for the cat processes to occur.
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-jjf
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That has been my observation. Between the closed-loop parameter on the ScanGauge and watching the (narrow band) 02 sensor on my
digital AFR, I see stoich almost all the time. In fact, the way I drive, I almost never see open-loop, even when I accelerate. I think the ECU "cheats lean" under steady-state conditions. When the ECU is chasing stoich, it will go rich by up to -0.2 below 14.7. On the other hand, I will sometimes see it momentarily go lean at +0.9 over 14.7 without me doing anything. There is a part of me that wonders if I trained the ECU to "drive lean" as a function of my driving habits.
CarloSW2