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Thread: Whipple 6.1 Hemi - Unexpected Injector PW dip at 4700-4800 RPM

  1. #1
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    Whipple 6.1 Hemi - Unexpected Injector PW dip at 4700-4800 RPM

    OK, so I've had this odd issue with 2 different boosted 6.1 Hemis now. One was a 2006 300C with a procharger, the other (that I'm currently working on) a 2010 Challenger with a whipple. Both of them have the pulsewidth dip, but the 300C occurred around 5275 - 5375 RPM. So, I'm not convinced that the dip is tied to the RPM variable.

    As you would expect from the dip in pulsewidth, it causes a momentary lean spot in the Air-Fuel ratio.

    I'll attach a tune and log file for the challenger below the image for anyone wanting to take a gander. I must be missing something obvious for this to happen on 2 different cars. Thanks for any input anyone can provide.

    The dip can be seen (uninterrupted by traction control) at marker 12:02:38. There's also an occurrence around 11:59:58, but it's somewhat interrupted by some slight wheel spin and traction control stepping in.

    Capture.PNG

    Challenger_WIP_v1.0.6.hpt
    Challenger_1.0.5.hpl
    Last edited by B00STJUNKY; 11-27-2019 at 02:56 PM.

  2. #2
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    This is a picture of the same thing occurring on the 300C. As you can see, it's a bit higher up in the RPM range, and the Pulsewidth is trending on an upward slope due to the nature of a Centrifugal SC vs a PD SC. But it's very plain to see the very similar dip in pulsewidth.

    300C.PNG

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    What does fuel mass cyl 1 do when it happens?

    Your MAP KPA and total airflow also dip slightly right there. But VE does not.
    Last edited by spoolboy; 11-29-2019 at 09:22 AM.

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    Fuel mass remains pretty constant, just now went out to verify. I did finally discover what causes the issue, though. And to me, it's pretty disheartening.

    So, I started out tuning on factory boosted applications (Neon SRT-4 mostly), and as such, I became very well acquainted with a lot of the tables that are more tailored for boost. One of those tables is the "Vac Mult" table under "Fuel Mass Multiplier" of the "Open Loop Base" tab. In the boosted applications (including Hellcats, though they are labeled and scaled as Pressure Differential, rather than Vacuum Multiplier), there are compensations made for manifold pressure that directly affects fuel mass delivery.

    In the Naturally Aspirated applications, these tables compensate for vacuum by multiplying by a correction factor less than 1.0, which decreases commanded fuel injector pulsewidth under vacuum conditions. When at atmospheric pressure, it has a correction factor of 1.0, meaning no change from base.

    In my tuning practices with boosted applications, I like to rescale that table according to expected boost range and apply a correction factor that will increase the commanded injector pulsewidth in boost just like it would in a factory boosted application.

    Now, for whatever reason, even with manifold pressure remaining constant, at some point in the RPM range (I don't know what else to tie it to, since VE and Fuel Mass remain pretty constant during the pull), it has that odd blip in the pulsewidth where it ought to remain constant.

    By setting the Vaccum Mult table back to stock, then compensating for the need for increased fueling at higher boost by sloping the injector scaling as pulsewidth increases, I have gotten a nice, flat, uninterrupted pulsewidth trend as would be expected. The same effect could be accomplished by sloping the VE table as load increases, rather than sloping the injector data. But it's not a perfect compensation either way. The VE table is based off of P-Ratio, so as altitude and atmospheric pressure changes, it will cause an offset in the built-in compensation. I'm sure the same could be said of sloping injector data, as well.

    In any event, long winded post, I know. But hopefully someone else finds this information useful at some point in their experience.

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    Log battery voltage?

  6. #6
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    Quote Originally Posted by spoolboy View Post
    Log battery voltage?
    The solution was mentioned in my post above. I haven't logged battery voltage, but I can't see inj pw offset compensation being the cause after seeing the results of putting the Vacuum Mult table back to stock and getting a solid, expected Injector Pulewidth curve. But, when the weather improves, I'll check it anyway just for the sake of confirmation.
    Last edited by B00STJUNKY; 11-29-2019 at 02:42 PM.

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    Here's what the curve looks like after changing the Vacuum Mult table back to stock.

    Vac_Mult_test.PNG