Mixture set with FV Video

[Funracer]

Just saw this it has come out in the last few months so new to me. He has same car I do 83SC with stock CIS with Lambda.

https://youtu.be/Vrg2VqPcc54?si=AomTPw4vPkj1mTI8

Skip to 5 minute mark. His Bentley (looks like page 240-06)has FV set to 45-65% with red to ground and black to green wire on the diagnostic port. My Bentley manual does not have this information.

I was under the impression we were using 40-45% for drivers (non race car). Can anyone confirm his Bentley info? Bentley has been known to be inaccurate.

If it is accurate my car is set too rich.

Thanks

[AndrewCologne]

All is explained here:
https://nineelevenheaven.wordpress.com/the-lambda-control-of-the-911-sc/

In a nutshell, ... if you set with ox sensor unplugged your initial CO to the specs of 0.4 - 0.8 % Vol. then with re plugged sensor and lambda activated the duty cycle at idle will swing around 55-60%. This means 55-60% equals Lambda 1 (closed loop).
And here lies the nub of the problem as if you accelerate the duty cycle jumps to a fixed value of 65% (open loop). And this will not result in an optimal Lambda of 0.85. and was not wanted due to emission restrictions. So just a little enriching when accelerating by still keeping less emissions.

Now, while lambda control is active and engine is idling, if you turn the CO screw CW until the duty cycle swings around 40 %, then with lambda control while normal driving it will be kept at lambda 1, means not too rich, but .... when accelerating the difference from 40% (= Lambda 1) to 65% will almost hit the wanted Lambda 0.85 for acceleration.

The sensor voltage reading in the video on the first view seems odd, as it should never exceed 1 volt. Here the wanted voltage with a hot running engine should swing between 0.2 and 0.8 volts.

[PeteKz]

Excellent info Andrew, thanks.

[Funracer]

Originally Posted by AndrewCologne

All is explained here:
https://nineelevenheaven.wordpress.com/the-lambda-control-of-the-911-sc/

In a nutshell, ... if you set with ox sensor unplugged your initial CO to the specs of 0.4 - 0.8 % Vol. then with re plugged sensor and lambda activated the duty cycle at idle will swing around 55-60%. This means 55-60% equals Lambda 1 (closed loop).
And here lies the nub of the problem as if you accelerate the duty cycle jumps to a fixed value of 65% (open loop). And this will not result in an optimal Lambda of 0.85. and was not wanted due to emission restrictions. So just a little enriching when accelerating by still keeping less emissions.

Now, while lambda control is active and engine is idling, if you turn the CO screw CW until the duty cycle swings around 40 %, then with lambda control while normal driving it will be kept at lambda 1, means not too rich, but .... when accelerating the difference from 40% (= Lambda 1) to 65% will almost hit the wanted Lambda 0.85 for acceleration.

The sensor voltage reading in the video on the first view seems odd, as it should never exceed 1 volt. Here the wanted voltage with a hot running engine should swing between 0.2 and 0.8 volts.

I am looking for the setting it would have left the factory with. So that would be 45-65% at idle then? This may be related to my cold start issue from the other thread.

Thanks

[AndrewCologne]

I am looking for the setting it would have left the factory with. So that would be 45-65% at idle then?

Check the info in the link and my answer. The factory default is 0.4-0.8 Co % Vol. at idle with the sensor unplugged, measured before cat. This gives you a duty cycle swinging around 55-60% at idle when plug is re connected to the sensor.

As you're referring to cold start, yes as like acceleration the cold start is also closed loop driven (65 %), the cold start will be affected as well if setting the duty cycle to swing around 40% at idle, it lets the cold start resulting richer, like at acceleration.