I have a VAFC I and I went to the local Honda Tuner to ask about him tuning it.. he has experience tuning Hondata's, dyno tuning, and other type of stuff, so I figured he would be an expert. Plus the fact he has owned an S before.

He told me that the VAFC will do nothing in the long run... something along the lines of making HP gains on the front end, but after a week or two, the ECU will relearn my driving and nullify the changes made by the VAFC. He said he could tune it for me but it would be a waste of my money.... he said that the ECU was so finely tuned from the factory that the VAFC will not really make a big impact. Plus the whole "ECU relearning" thing.

What are your opinions on this? Is he telling the truth? I don't see any reason why he would lie since this was an opportunity for me to give him business.

 

This just means that he isn't qualified to tune it. The OEM ECU will un-tune the V-AFC if it isn't configured properly. A "perfectly" tuned V-AFC on an '01 will give very nice gains across the whole fuel curve (10+ peak).

 

Hmm.. I don' think there are any qualified VAFC tuners in Memphis then. I know some tuners that could figure it out, but I don't believe any of them have had experience with the VAFC, especially on the S.

Do you happen to know any qualified tuners close to Memphis, TN?

 

I don't even know where Memphis is! Honestly, if the "tuner" knows how to tune anything on anything (and uses a WBO2 to do it), then he can tune a V-AFC on an S2000l. The problem is that the V-AFC needs to be setup to not alter the MAP voltage while the ECU is in closed loop. I had best results when the V-AFC did absolutely nothing below 80% throttle (the default is 10%).

I don't have the V-AFC anymore. I designed my own piggy back using similar technology, but that tunes itself using a WBO2 input. Anyway, I am fully aware of the benefits and deficits of the V-AFC on the S2000.

 

Let me see if I am drawing the correct conclusion... are you saying that if I use the VAFC to only control activity at throttle open at 80% or more, I will not have the problem of the ECU trying to re-set the VAFC because at this point it is out of closed loop operation? Or am I just totally off....

I found a guy in town that knows how to use a wideband to tune the VAFC because he used to and still tunes his Type-R that is using the VAFC. I know another guy that is also familiar with tuning with the wideband, and does it professaionlly from time to time for other apps (but not VAFC specifcally).

 

That is exactly correct. I don't know the exact throttle position (50%, 60%, etc.) that causes the ECU to go to open loop, but I found that 80% works perfect. I set the Lo position at 80% and the Hi position at 81%.

On second thought, there was 1 thing that you stated a bit incorrectly. The ECU doesn't re-set the V-AFC. What it does is recalibrate itself to negate the effects of the V-AFC if fuel corrections are made while the ECU is in closed loop.

 

i'd like to hear more about this


i also have several questions... do the s2k ecus give timing bonuses based on fuel taken away?

are there any other piggybacks besides the greddy offering that control timing direcly or indirectly?

also... to the original question... technically only the closed loop fuel trims will be unlearned... and you only set those roughly anyway, you can find tune them if you're anal but that would require you doing lots of logging and tweaking.

the afc should be used to tune wot situations and the partial throttle areas are simply interpolated by the afc.

 

Or you can pull your backup fuse once a week...

 

I believe that the ECU does advance the timing in some cases if the tuned fuel curve is flat enough. Lean spots in the fuel curve (due to VTEC adjustment and / or "resonant humps") can cause the ECU to go conservative on timing, so proper tuning can prevent that.

I don't agree with your statement about fuel trims. Short Term Fuel Trim doesn't have any impact on WOT, but Long Term Fuel Trim does. The ECU "learning" is just the ECU adjusting LTFT. If you setup the VAFC to NOT do anything in closed loop, it won't have any impact on LTFT, so the ECU will not "unlearn" anything.

 

^ you might have misunderstood what i said...

i'm saying the closed loop fuel trims should be the only ones that have a possibility to be unlearned (same thing you said) so setting the lo hi points are really improtant so you don't have to bandaid anything by pulling fuses.

also... the short term fuel trim (if monitored) will show you how much afr variations and corrections are being made. this value usually dances around a given area that should be well known and accepted. if you're tuning a vafc you should put the vafc to where you aren't making any of these dancing values go off and hence get "learned" into long term fuel trims. in all technicality it wouldn't matter because it's just closed loop stuff but it's the "right" way to do it. technically i don't think s2ks have anything to worry about in that dept as you usually don't see s2ks upgrading injectors. but if you went turbo and wanted to tune with the vafc, this would be the right way.

otherwise everything is left up to the lo and hi points. you said it best. you don't want the closed loop corrections to overlap the wot hi map on the vafc... so you must set it correctly so there is no overlap and hence the vafc setting stay the same.