3.2 O2 Sensor on 1984 911, broken!!???
05-12-2008, 01:04 PM
#16
The base mixture is set with the O2 disconnected and then adjusting the mixture screw on the AFM (not the idle screw on the Throttle Body). In my car I have a wideband O2 sensor and monitoring system installed, using the WBO2 reading I simply set the base mixture to 14.5AFR. (Slightly Rich)
The factory procedure uses CO to set this to a value of 0.8co +/- .2
Once this is set the car will idle at this setting.
The O2 sensor is used in USA cars to help keep the target AFR at 14.7 for best emissions. This target value is being achieved by the DME looking at the O2 signal and fine tunning the mixture. It does this at idle and part throttle under light load.
The O2 signal is ignored at Wide Open Throttle and also appears to be ignored in part throttle heavy load, I'm not 100% on this part throttle heavy load but from my WideBand O2 readings it seems to still dip into the 13.2 range under acceleration and not in WOT.
My advice is simply this: if you run a CAT in your car use the O2 because if the mixture gets altered from an air leak, FuelPressureRequlator failure or somthing else you could go rich for an extended period of time and not know this. Without the O2 sensor you have no compensation and risk damaging the CAT. If however you do not have a CAT I'd disconnect the O2. In my 3.2L car I have no CAT and run the DME without the O2 sensor all the time. As a matter of fact I have my WideBand O2 sensor installed in place of the stock Narrow Band sensor.
In closing, if you disconnect the O2 then have the base CO set to .8 or the AFR to about 14.2
Here are a few CO to AFR conversion values:
CO = AFR
------------
.1 = 14.7
.8 = 14.2
2.5 = 13.5
The factory procedure uses CO to set this to a value of 0.8co +/- .2
Once this is set the car will idle at this setting.
The O2 sensor is used in USA cars to help keep the target AFR at 14.7 for best emissions. This target value is being achieved by the DME looking at the O2 signal and fine tunning the mixture. It does this at idle and part throttle under light load.
The O2 signal is ignored at Wide Open Throttle and also appears to be ignored in part throttle heavy load, I'm not 100% on this part throttle heavy load but from my WideBand O2 readings it seems to still dip into the 13.2 range under acceleration and not in WOT.
My advice is simply this: if you run a CAT in your car use the O2 because if the mixture gets altered from an air leak, FuelPressureRequlator failure or somthing else you could go rich for an extended period of time and not know this. Without the O2 sensor you have no compensation and risk damaging the CAT. If however you do not have a CAT I'd disconnect the O2. In my 3.2L car I have no CAT and run the DME without the O2 sensor all the time. As a matter of fact I have my WideBand O2 sensor installed in place of the stock Narrow Band sensor.
In closing, if you disconnect the O2 then have the base CO set to .8 or the AFR to about 14.2
Here are a few CO to AFR conversion values:
CO = AFR
------------
.1 = 14.7
.8 = 14.2
2.5 = 13.5
Last edited by scarceller; 05-12-2008 at 02:24 PM.
05-12-2008, 03:46 PM
#17
Rennlist Member
In addition to Scarcellar's post, the three-way catalytic converter replaced the already in-use two-way cat (in 1980), because the two-way cat would be ineffective in reducing NOx emissions to meet regulatory changes for the 1981 model year. Enter the stoichiometric point, the theoretical point at which combustion is complete. In other words, through oxidizing, all the carbon (C) is burned to become CO2, and all of the hydrogen (H) is burned to become H2O, etc. The 3-way cat works best when it receives exhaust from an engine that is running slightly lean, above the stoichiometric (ideal) point, which is between 14.8 and 14.9 parts air to 1 part fuel. When more than the required amount of oxygen exists the engine is running “lean,” which favors the above two oxidizing reactions. When excessive fuel is present the engine is running “rich,” at which point the cat favors the reduction of NOx.
Enter the oxygen sensor. Originally called Lambdasonde by its developer, Bosch, it is a sensor probe that installs into the exhaust just before the catalytic converter. The oxygen sensor measures the remaining oxygen content in the exhaust, and then sends corresponding signals to an electronic control unit (ECU). The ECU is then able to make fine adjustments to fuel delivery, and keep the fuel injection system as near as possible to the ideal stoichiometric point.
Porsche’s use of the 3-way cat and Lambda was so effective that for the first time since 1975 no smog pump (auxiliary air injection) was required in order to meet emission requirements. Depending on what the smog laws are in a particular state, modifications are either temporary or permanent. In CA if we want to keep the car registered for street use, and use the car on the track, we really jump through hoops to do both. Here, with our traffic levels, it's all about emissions, and that, in turn, is all about O2 sensors, ECUs and precise tuning.
Enter the oxygen sensor. Originally called Lambdasonde by its developer, Bosch, it is a sensor probe that installs into the exhaust just before the catalytic converter. The oxygen sensor measures the remaining oxygen content in the exhaust, and then sends corresponding signals to an electronic control unit (ECU). The ECU is then able to make fine adjustments to fuel delivery, and keep the fuel injection system as near as possible to the ideal stoichiometric point.
Porsche’s use of the 3-way cat and Lambda was so effective that for the first time since 1975 no smog pump (auxiliary air injection) was required in order to meet emission requirements. Depending on what the smog laws are in a particular state, modifications are either temporary or permanent. In CA if we want to keep the car registered for street use, and use the car on the track, we really jump through hoops to do both. Here, with our traffic levels, it's all about emissions, and that, in turn, is all about O2 sensors, ECUs and precise tuning.
