I am new to tuning and really don't know what everything means and does with the AFC, can someone breakdown what it does and how to use it? Also, can someone please tell me how your AFC is set-up (specifically)?

DRAG III
AEM Fuel Rail
Magnecor Wires
MSD-BTM Ignition
12:1 FMU
Inline Pump
S-AFC

 

Unless you have a specific question, its gonna be a lot easier for someone to show you in person.

 

I was wondering the same thing about this? Does this unit actually control the air/fuel ratio throughout the whole rpm band? Will it make a car essentially run near perfect ratio once installed and tuned all the way up to redline? Last question is, HOW does this unit control air/fuel flow exactly?

 

OK, i really dont have time to type all this but i'll try to break it down for you guys that are new at this. In case you cant tell after reading this, i love vafcs. No **** its not as adjustable as a $1000+ standalone but for $350 you cant beat it. OK--->

Yes, you can adjust the fuel in percentages thruout the entire rev range at user definable rpms.
For example: You can richen it up 5% at 4k, and 10% at 5k. If you are in between 4 and 5k, it will just interpolate between the 2 settings. You can also set two entirely different fuel maps for wide and low throttle, and pick the points when it switches between the 2.
For example: you can set it so under 20% throttle, it uses a map that is pretty lean. This is good if you want to save gas under everyday cruising. Then, you can set it so that over 60% throttle it will switch to your wide fuel map which you have tuned for power. Between 20 and 60% throttle, it will interpolate between the two.

The vafc uses 3 main sensors to function:
1] throttle position sensor
-used to figure out which fuel map it should be using. ex: it knows how much
your smashing the gas peddle.
2] rpm signal
-used to figure out what fuel setting to use. ex: if you have it set to lean at 5k,
and richen a little at 7k, it knows what rpm your at so it can make the propper
adjustment.
3] map sensor
-this is the important one. Your computer uses the map sensor signal to
determine how much fuel to give the motor. If your throttle is closed, there
is more vacuum in the manifold, and the map sensor gives out a lower voltage.
The computer sees low volts and knows that it needs less fuel. The way the
vafc works is very simple: it just takes the voltage from the map sensor and
either lowers or raises it to make the computer give the motor the amount of
fuel you want.


The vafc does not controll air in any way like the name implies, but just the acompanied fuel. With a decent a/f gauge, you will be able to tune your car to about 90% optimal air/fuel ratio. With a wide band oxygen sensor and meter,
you will be able to fine tune it that extra 10%, which as everyone knows that last few HP are hiding On a stock car, you'll find that you need to lean it out about -5% across the board - nothing major. Where these units really shine is if you just installed that new throttle body and set of wilder than stock cams. You'll be able to bump up the fuel a notch up top to compinsate. (and in the case of cams, bump up the x-over if vtec applicable).
If your planning on buying a vafc/safc (all of the above applies to the fields sfc as well) then spending the extra $50.00 on an a/f gauge is a must do.

 

Thank you VERY much for the informative crash course, my only other question is do I keep the vortech FMU in place? or will it confuse the whole setup of the AFC?

 

Good info, i still dont understand how the "vafc hack works" in simple terms.

 

ok, you already know that the vafc works by modifying the voltage from the map sensor. So with the 450 injectors in place, you need to reduce the voltage a whole lot to get them to idle and run right (-40%). Ok, clear on that much?

When the throttle is closed and there is vacuum in the manifold, the map sends out a lower value (ie: less fuel). Once you step on the gas and the vacuum dissapears, the computer gives more fuel. At full throttle, your at 0 vacuum and the computer is supplying maximum fuel. The problem is, with a turbo your gonna go over 0psi once you start boosting. If the computer was dumb, it would just keep increasing fuel as the map sensor voltage rose. Unfortunatly its not, and it put the car in safe mode because it thinks the map sensor is broken. Still following me?

Ok, so since you have the map sensor signal tuned so low to begin with to run the 450s, you have plenty of room to work with. The computer keeps adding fuel as the map sensor voltage rises, but since you have the voltage reduced so low it never gets to the point where the computer thinks the map is broken. (well, not NEVER, but you get enough room for 10psi). As far as the computer knows, everything is still perfectly fine.

Let me know if you didnt get any of that. Its really quite ingenious how it works. Its so freaking simple its amazing.

 

tahnks again, i completly understand now. How come people say you can only use dsm injectors for the hack?

I appreciate your time. Its interesting to know how these work. I used to have one, but it got jacked along with the car. Now I am gettin hondata 2b.

 

You can use any larger than stock injectors, not just the DSMs. The DSMs are just so popular because of the price. Hell, i only paid $3.00 for mine at the u-pull it yard

The thing is, the 440/450 sized injectors are a perfect match for the vafc mod.
If you had something like 310 or 360 injectors, you might only have to lean it out
around -30% to make them run good. The problem is that the less you lean it out, the less room you have on top for boost. At -40%, you push around 10psi before the voltage passes the "broken map" level. At only -30%, you will only have enough room up top to boost about 7psi. For someone with a greddy kit who already has 310(?) injectors, and is only planning on boosting 5psi or so, it would still work out fine.
Now the problem with using something like 550cc injectors, is that the vafc will only adjust to a maximum of -50% which is almost, but not enough to idle them. You could use 550s though if you have an fpr to lower the pressure enough so that -50% would be enough. I dont know how the idle quality would be though, probably not perfect. My DSM 450s idle pretty much like stock.

And i know there are people about to reply "just get a hondata/zdyne". Yes we all know hondata works great but the whole idea here is to give people who already have vafcs some ideas to work with the equipment they already have.

 

thanks again, this thread should go into the newbie archives since you have explained it so well in simple terms. I have read every singel thread covering this and only this one i fully understood.

 

yeah, i actually understood that stuff.

 

Thanks