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Thread: Fuel dynamics mafless?

  1. #31
    Lifetime Member swingtan's Avatar
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    To be honest, I wouldn't think that was too bad. There are twp things that I can see though.

    1. Delay between the commanded AFR anf the WB AFR:
      At throttle close, the air speed through the motor will slow down, so the WB signal will lag the rest of the engine parameters. The mount of lag is determined by the position of the sensor. Obviously, the further away from the motor it is, the more lag will be present in the log data. So this probably isn't a huge issue and I'd not be overly worried about it.
    2. Slight richening of the WB AFR signal on throttle close:
      In the E38, this is controlled to some degree by "Wall Wetting Asymmetry Factor". Low values in this table add less fuel when the throttle is closed. Again, your log only shows a very mild increase in richness.

    To really work on dynamics, you need to look at...
    • RPM
    • MAP
    • TPS
    • Airflow
    • Inlet Valve Temp. ( though this can be guesstimated for systems that don't have this PID ).




    Simon.

  2. #32
    Lifetime Member mr.prick's Avatar
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    Quote Originally Posted by Highlander View Post
    The way to cure it would be to reduce the minimum injection pulsewidth. Try that out.
    Interesting.


    Quote Originally Posted by swingtan View Post
    To be honest, I wouldn't think that was too bad. There are twp things that I can see though.

    [list=1][*]Delay between the commanded AFR anf the WB AFR:
    [indent]At throttle close, the air speed through the motor will slow down, so the WB signal will lag the rest of the engine parameters. The mount of lag is determined by the position of the sensor. Obviously, the further away from the motor it is, the more lag will be present in the log data. So this probably isn't a huge issue and I'd not be overly worried about it.
    I've thought about the possibility of the exhaust pressure rapidly reducing when the throttle is slammed shut or when the clutch is depressed, engine load rapidly reducing causing this.
    The smoother TP% decreases the smoother AFR ramps back to commanded.
    It's more pronounced when shifting gears during PE,
    AFR gets quite rich but it's better than having DFCO on and
    the harsh re-engagement of the clutch.

    It may not be that big of a deal, LTFTs and PE AFR are where I want them
    it just makes a log look a little ugly.
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  3. #33
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    Quote Originally Posted by Highlander View Post
    This is some valuable info. People don't seem to get the importance to dynamics section. I broke an engine because of it. I learned this tables the hard way.
    Broke an engine due to dynamics! How did that happen?

  4. #34
    Lifetime Member swingtan's Avatar
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    Quote Originally Posted by mr.prick View Post
    It may not be that big of a deal, LTFTs and PE AFR are where I want them
    it just makes a log look a little ugly.
    That looks better than some of mine. I've been thinking about closed throttle fueling today and need to do some testing......

    Quote Originally Posted by gmh308 View Post
    Broke an engine due to dynamics! How did that happen?
    I reckon this could happen if it went very lean on throttle tip in. Massive lean spike and heavy load resulting in predetonation. This would destroy a piston pretty quickly. I know when I was messing around and had a big lean spike, it would feel like hitting a brick wall when smacking the throttle on gear changes. Needless to say I didn't like that very much.

    Simon.

  5. #35
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    Engine was a boosted engine. Customer was wheel spinning and he was pushing in gradually the throttle. Car went lean ~13.8:1, massive knock. This was before we had access to the dynamics section. I had this same issue with a colorado turbo with an E67. We already had access to this and we were experimenting with it. I fixed it using impact factor 0% ethanol. All other tables had absolutely NO effect on super lean while modulating the throttle.

    I have another boosted vette that I will deal with very shortly and will post the results on it. I don't want to make the same "mistake" twice (although it was NOT my fault).
    "All that is needed for the triumph of evil is that good men do nothing..."

  6. #36
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    What bothers me out of all this is that GM's ZR1 has basically STOCK Dynamics section. Even for a boosted engine... GRRR...
    "All that is needed for the triumph of evil is that good men do nothing..."

  7. #37
    Lifetime Member swingtan's Avatar
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    Quote Originally Posted by mr.prick View Post
    I've not seen any changes to fueling after altering the impact factor or evap time.
    Maybe it's my technique.
    How would you cure this?
    Just wondering what your PE ramp out rate is like. If you increase the ramp out rate, it might help to speed up the return to the commanded AFR.

    Simon.

  8. #38
    Lifetime Member mr.prick's Avatar
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    It's pretty much instant.

    The more I think about it the more I lean towards it being pressure differential in the exhaust.
    I know O2s are pressure and heat sensitive.
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  9. #39
    Lifetime Member mr.prick's Avatar
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    Playing w/RTACS & {B3605} (impact factor) I found that it would have an effect on fueling but only in OL.
    Once PE ramped out and EQ1 was commanded it had no effect and AFR was still rich
    even though IBPW was low.
    If you look at the chart I posted previously you can see what I mean.

    The lean tip-in can be reduced w/{B3406] but not the tip-out.
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  10. #40
    Lifetime Member swingtan's Avatar
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    What OS / Tune file are you working on? I can't find either of those in COS-3 or the E38 tune I use......

    I'v e been looking at dynamics a bit more and found another interesting point.

    When running CL, if you get a large rich spike on throttle close, the O2's will pull a massive amount of fuel to bring the AFR's back to where they should be. If you then snap the throttle open again, you get a huge lean spike, as the O2's have pulled all the fuel out.

    Reducing the impact factor / dynamic fueling and increasing "Wall Wetting Compensation" reduces the rich spike, which reduces the O2 correction and in turn reduces the lean spike on the next throttle opening.

    I still think that the increase in richness in your example if just residual fuel in the intake at throttle close. You may be able to improve the fueling by altering settings to let the controller know that there is more fuel available to the cylinder at very low MAP settings. In the LS1, you would reduce the figures in B3401 and in the E38 you would increase the figures in B2014. In both cases just the 20kPa column would need adjusting.

    I might try loading a bog stock tune in my car and see how the dynamics react, then try tuning them ( if needed :p ).

    Simon.

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