[Diy_efi] O2 says rich, car runs lean.

[Gary]

Going Open Loop at WOT has little to do with the accuracy of the 
OEM NB O2 sensor. The purpose of the OEM sensor is to send 
feedback to the P(or E)CM during Closed Loop operation, letting 
it know whether the mixture is either lean of or rich of stoich or 
IOW, ~14.7. Therefore, the function of OEM sensor is that of a 
switch. That switching is performed around stoich. The sensor is 
constantly dithering from rich to lean of stoich with the PCM fuel 
command constantly adding and then removing fuel. There are 
OEM calibrations that are designed to operate in 100% CL mode. 
This impies regardless of the mode of operation,  it is maintaining 
~14.7 AFR. One such vehicle is a new turbocharged setup that
Chrysler markets.   

BTW, the voltage OEM NBO2s send back to the PCM has been 
used to tune the AFR for performance use. It should be understood
however, it is not a very reliably accurate means to verify AFR. I 
want to stress reliable here. The further from stoich the AFR strays, 
the more temperature sensitive they become, and the more impact 
temp will have on their accuracy. To consider them accurate without 
any knowledge of when they might be, makes any accuracy they 
may posess, of questionable value. Depending on the temp the sensor 
is exposed to, the AFR accuracy can vary easily by over a full #. In 
addition, the further from stoich NBO2s venture, the more impact 
very slight voltage changes will have on actual AFR, thus giving the 
same effect as lowering resolution and dulling sensitivity.   

GAS


----- Original Message ----- 
From: "John Smith1882" <dirtrider218 at hotmail.com>
To: <diy_efi at diy-efi.org>
Sent: Monday, June 12, 2006 1:39 PM
Subject: Re: [Diy_efi] O2 says rich, car runs lean.


> Just some personal observation that may support this....Something I've 
> noticed is that many OEMs omit O2 sensor input at wide open throttle 
> and run on the fuel table without feedback mixture adjustment. This 
> would make sense since the narrowband is only accurate during lean 
> cruise and WOT/high load would require AFRs richer than 14.7:1. 
> Am I on the right track?