1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Vafc Fix

Discussion in 'Forced Induction' started by buzz1167, Jul 13, 2004.

  1. buzz1167

    buzz1167 Member

    Messages:
    48
    Likes Received:
    0
    Joined:
    Jul 2, 2004
    Location:
    Kansas city, Ks
    I've heard some about the "vafc jerk" and I think I've got it fixed on my car. I have an automatic, so I'm not sure exactly who else has the problem. But the problem I had was when you let off the gas while your cruising down the highway, and then when you get back on the gas, it jerks becuase the computer screws up the fuel mixture.
    Anyway I figured the computer had a second idle program (becuase I know it idles different in park than it does in drive, becuase I can look at my a/f meter and tell). So what I did was I put the car in park and revved it to 3000rpm (anywhere around there is ok). I noticed that after a few seconds it jumped around all over the place. So I thus determined that *this* must be the problem. So I richened the mixture (at partial throttle setting) until the computer would no longer lean out the mixture (the jumping was caused by an intermittant lean mixture). I got all the way to about -30 (up from -39). SO I drove around and noticed that for a minute it was ok, but then it came back. So I retested, and determined that the L.T.F.T. had adjusted (leaned it out) over the period of a minute or so causing it to jump around again. Thus I revved to 3000 again and continued richening up to -25 where it stopped bouncing again. Now the jerk is gone, and it didn't happen for about 2 hours of driving.

    Now the problem is that the curve is too high to boost very much. I will overcome that obstacle when I come to it, but I'm pretty sure that I will use the 'Load determined vtec' in the vafc. I'll set the default vtec crossover to 4500 (closed loop begins) and then set the auto load transfer to 0psi (or wherever I decide works best). That will give me an easy 'boost map' to get rid of all that partial thottle increase and make sure the CEL doesn't come on if there is boost during partial throttle. This will fix the problem (I think) becuase the vafc will put the car on the 'vtec map' whenever the car goes past 0psi, thus giving me a seperate 'boost map'. Great isn't it?
    Be in mind that I don't have vtec, so this setting won't actually DO anything, it will just serves to give me a free different map that is used only under boost.

    Btw: I have some odd throttle settings, I think I have 72% for WOT and like 20% or so for partial (I'm not sure that matters, but I'll check tomorrow)

    Hope this helps anyone who has had this problem, Tell me if it works for you!
     
  2. xj0hnx

    xj0hnx I wanna be sedated VIP

    Messages:
    14,172
    Likes Received:
    48
    Joined:
    Nov 10, 2002
    Location:
    C.C.TX.
    So...did you do any of this on a dyno with an actually wideband o2 snsor? Because A/F gauges are not acturrate measures of A/F, only the voltage the o2 is sending out to the ECU based on what it is reading.

    And this...



    Just doesn't make any sense at all.
     
  3. buzz1167

    buzz1167 Member

    Messages:
    48
    Likes Received:
    0
    Joined:
    Jul 2, 2004
    Location:
    Kansas city, Ks
    Whats the problem again? A narrowband a/f meter works just fine, you don't need a wideband to tell if you're rich or lean, If you want real numbers then you need one, I'll agree. But all I needed to do was to make it rich enough to stop the ecu from trying to correct itself.



    Ok I'll try and decipher that B)

    If you set your vtec type to type 3, then you can make vtec engagment based on rpm, throttle position, and Map sensor voltage (engine load).
    If the vtec is set to 'engage' at 0psi, then everything above 0psi will be tuned on the seperate 'vtec' fuel correction table. Being as the narrow throttle is now set really high (-25), you can't boost very much without throwing a code. So you use this vtec (set at 0psi) to change the corrections only when you're on boost. This way you can put the numbers back where they need to be and you don't throw a code when you transition into/out of boost, becuase a little boost will linger after you let off the gas a bit.
    And being that you aren't actually using the vtec engagement to turn on vtec, their all just funny numbers that make it work.

    Better?
     
  4. xj0hnx

    xj0hnx I wanna be sedated VIP

    Messages:
    14,172
    Likes Received:
    48
    Joined:
    Nov 10, 2002
    Location:
    C.C.TX.
    Are you using a VAFC, or a VAFC II?
     
  5. buzz1167

    buzz1167 Member

    Messages:
    48
    Likes Received:
    0
    Joined:
    Jul 2, 2004
    Location:
    Kansas city, Ks
    Vafc II, Didn't realize there was that much of a difference between them, but I guess the type 3 vtec is one of those, or it seems it would be.

    Anyway, if you've got the problem, this should help no matter what vafc you've got. The whole boost fixing situation could be different.
     
  6. xj0hnx

    xj0hnx I wanna be sedated VIP

    Messages:
    14,172
    Likes Received:
    48
    Joined:
    Nov 10, 2002
    Location:
    C.C.TX.
    Yea, the first VAFC didn't have different vtec types, just lo to hi throttle and hi to lo throttle settings.
     
  7. hybrid89

    hybrid89 thistownsucks...

    Messages:
    1,821
    Likes Received:
    1
    Joined:
    Jan 8, 2003
    Location:
    SoCal
    who taught you how to tune? 70%WOT? WTF?
     
  8. xj0hnx

    xj0hnx I wanna be sedated VIP

    Messages:
    14,172
    Likes Received:
    48
    Joined:
    Nov 10, 2002
    Location:
    C.C.TX.

    The hack use's something like 98% lo and 99% wide. All that is, is telling the VAFC when to kick in the fuel maps in relation to throttle position.
     
  9. buzz1167

    buzz1167 Member

    Messages:
    48
    Likes Received:
    0
    Joined:
    Jul 2, 2004
    Location:
    Kansas city, Ks
    Lol, honda taught me how to tune. Alot of honda ECU's consider 72-73% as WOT. And thus they change fuel maps right there. Its best if you do too, otherwise your just screwing it up, fighting for a lost cause trying to map 2 seperate fuel maps with one of your correction maps.

    They also change into open loop at a certain rpm (4500 on mine). Witchever comes first. Usually the throttle though.
     
  10. [Freemantle]

    [Freemantle] Senior Member

    Messages:
    282
    Likes Received:
    0
    Joined:
    Apr 3, 2004
    Location:
    Vero Beach, FL
    The ECU will trip into open loop (lookup mode) from either engine speed (generally above 4000 RPM) and MAP sensor voltage. Once you are in Open loop, you use strictly the tables. In closed loop, the ECU uses the table for a reference but makes correction based on speed-density calculations. There is only one table to begin with (unless you are VTEC, which he is not. He's just abusing the HI-cam setting for a boost map).
     
  11. buzz1167

    buzz1167 Member

    Messages:
    48
    Likes Received:
    0
    Joined:
    Jul 2, 2004
    Location:
    Kansas city, Ks
    My golly, he's got it. ;) Well almost, I know that there is only one table that you modify on the ECU for your fuel map, but it does change; it doesn't just ignore the other sensors after it gets to 4500rpm or 72% throttle. (Sorry if that's not what you meant, but thats how I read it.) It takes the numbers and multiplies them by something to acheive a rich mixture so you can have better acceleration. I don't know exactly what it's going for becuase I don't have a wideband.

    I just heard about this whole, afc hack problem. I've seen an article on it somewhere, and the people on it seemed to have the mentality of 'its just part of having the hack'. I just figured after I screwed around enough and got mine smoothed out, I'd share the wealth in case anyone here has had the problem and has been faced with that same mentality.

    P.S. Oh, and realized I miswrote earlier, I wrote that it goes into closed loop after 4500, I meant to say Open... It's edited...

    HTH
     
Verification:
Draft saved Draft deleted

Share This Page