Please correct me if any of below is wrong...because this doesn't make sense to me:

-the stock ECU always try to maintain 14.7 A/F ratio in open loop mode (non-WOT)
-most people with VAFC say they use it to lean out the stock air/fuel mixture. I also heard most N/A application should shoot for ~13 A/F ratio.

This confuse me....isn't 13 A/F ratio is RICHER than 14.7? How comes they say they are trying to leaning it out.

I'm thinking about getting a VAFC because my carsound cat got destroy only after one track event. Apparently my cat is soaked by fuel
So i think i need a VAFC to lean it out....but this 13 A/F ratio confuses me...

 

14.7 is considered the stoiciometric ratio but your engine probably won't like to be that lean most of the time due to non perfect combustion. Just like if our engines had perfect combustion the catalytic converter wouldn't let out any emmisions however they still do.

I think the engine usually hangs around the 12s for most of the RPMs in a stock-like setup.

EDIT: The goal in tuning the V-AFC should be more in smoothing out the torque curve, not in maintaining a specific air/fuel ratio. The A/F readings will help you determine which way you need to go to get more power but that's about all, sometimes a certain ratio will make the most power and other times it won't.


[Modified by SurferX, 12:01 AM 5/24/2002]

 

so that means the stock ECU is not really doing it's job? It's supposed to monitor the first 02 sensor and adjust the fuel constantly to get 14.7 ratio...

Can somebody give any overview of how to tune an VAFC on dyno?
Like what to do depending on certain torque curve, A/F curve, graph smoothness,etc.
And how do i calculate how much to adjust?

Notice i'm not asking about what's YOUR setting....of course the answer would be ----> go to dyno

 

I tunned my car to 13.5:1 air fuel ration. I did not gain any power from this, but better fuel consumption and less carbon on my rear bumper.
EVIL

 

closed loop = cruise/low load
open loop = WOT

AFC is used to tune WOT operation and sometimes idle situations

Once in closed loop, it will have some effect if new settings were applied however
the ecu would override it anyway.

The ecu does not alter a/f ratio in open loop since it ignores the o2 sensor during
that time.

 

Steve,

This is the first time i heard VAFC does not affect light throttle operation. Are you sure about that? Because supposedly VAFC can affect FOUR mapping HiCam/LoCam and light throttle/full throttle. If that is true, that half of the VAFC function is not as advertise...

Also can you in generally tell how to tune a VAFC, by looking at the various curve.
Is shooting for a constant A/F ratio more important or trying to smoothing out the curve? What A/F ratio do you recommend to shot for?

 

all the afc does is fool the ecu into thinking its at a different load point.
Once its there at part throttle(closed loop) it will just cycle the a/f to try to
maintain stoich. You are mistaken if you think the afc adds fuel, it fools the
ecu into possibly doing so, but if the ecu reads from a load point that has less
fuel than the one it was originally at, it will not be richer.
Another problem going to + side at wot, you can overload the map sensor
voltage to the ecu causing it to think the map is defective.

 

Thats the explanation I've been waiting for sgt. I have always heard that V-AFC's were much better for going to the neg. side but no one could ever back it up and give me a reason why.