johnnyttype
Active Member
- Joined
- Apr 18, 2007
well the way i always understood it was that the o2 readings at WOT r merely for tuning purposes but now everyone on the board is starting to say it is very bad to tune using the stock narrow band sensors. the big thing now seems to be wideband tracking of A/F ratios. 1000 times better than tuning with a scanmaster and millivolts (which i still do aswell)
This is from Vortex buicks:
The sole function that the oem sensor performs is to signal the ecm if the exhaust gas passing over the sensor is either rich or lean with the stochiometric A/F point of 14.7 being the dividing line. It simply acts as a switch that is used to correct fueling at part throttle to optimize mileage and emissions. It is NOT used to determine fueling at wide open throttle.
Not only is the sensor extremely insensitive on either side of stochiometric, it is also affected by exhaust gas temperature. As the sensor heats or cools, its output voltage changes even if the A/F ratio does not.
Trying to use the output voltage of the stock sensor to determine an optimum A/F ratio for a given car is essentially a futile exercise due to the very nature of the sensor and the changes that may be incurred with temperature swings.
When someone says that the fueling should be adjusted to some magic number such as 765 mv, the above curve will show the futility of that effort. 765 mv might be anything from an air fuel ration of 14 to 1 to 12 to 1, or even broader depending upon the individual combination, the exhaust gas temperature, and the condition of the sensor, etc.
Note that when someone says the O2s should be 800 or whatever other magic number they like, they are referring to wide open throttle O2s. My experience has shown that Alky Injection has allowed me to safely run lower O2's on the oem sensor.
My best advice is to buy a wideband O2 in order to obtain meaningful air/fuel ratios for consistent tuning as using the factory O2s for tuning is simply a meaningless exercise except in the very broadest sense.
This is from Vortex buicks:
The sole function that the oem sensor performs is to signal the ecm if the exhaust gas passing over the sensor is either rich or lean with the stochiometric A/F point of 14.7 being the dividing line. It simply acts as a switch that is used to correct fueling at part throttle to optimize mileage and emissions. It is NOT used to determine fueling at wide open throttle.
Not only is the sensor extremely insensitive on either side of stochiometric, it is also affected by exhaust gas temperature. As the sensor heats or cools, its output voltage changes even if the A/F ratio does not.
Trying to use the output voltage of the stock sensor to determine an optimum A/F ratio for a given car is essentially a futile exercise due to the very nature of the sensor and the changes that may be incurred with temperature swings.
When someone says that the fueling should be adjusted to some magic number such as 765 mv, the above curve will show the futility of that effort. 765 mv might be anything from an air fuel ration of 14 to 1 to 12 to 1, or even broader depending upon the individual combination, the exhaust gas temperature, and the condition of the sensor, etc.
Note that when someone says the O2s should be 800 or whatever other magic number they like, they are referring to wide open throttle O2s. My experience has shown that Alky Injection has allowed me to safely run lower O2's on the oem sensor.
My best advice is to buy a wideband O2 in order to obtain meaningful air/fuel ratios for consistent tuning as using the factory O2s for tuning is simply a meaningless exercise except in the very broadest sense.
