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Thread: Big off idle stumble, whatt first? IFR? calc.vet? Something else I'm missing?

  1. #91
    Joe (Moderator) joecar's Avatar
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    What year/model/vehicle do you believe your stock tune came from...?

  2. #92
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    01-02 Chevy Express Van.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  3. #93
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    And because I'm not struggling enough already, I went and snagged a newer style 4 wire MAF so I don't peg at sea level. I am curious though, since this one has integrated IAT, I can still wire it without said IAT correct? My IAT is downstream of the blower where it belongs.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  4. #94
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    Quote Originally Posted by Supercharged111 View Post
    And because I'm not struggling enough already, I went and snagged a newer style 4 wire MAF so I don't peg at sea level.
    The new MAF you 'snagged' won't make any difference... your OS has limits which you can't get around.... 512g/s airflow and 12,000hz raw frequency. You'll still peg exactly the same with your new MAF (that's if you even get there with your low boost). Save yourself some headaches and keep the original MAF in place. The only real way to get around pegging the MAF is to use a larger MAF tube if you hit the frequency limit... it will lower the frequency response and prevent you hitting that limit. Scaling the airflow and fueling will stop you hitting the airflow limit.

  5. #95
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    I was under the impression that this larger MAF with its larger tube would have that effect right off the bat and then I could rescale until it matched? Then again if I rescale the stock MAF like I was supposed to it may give me the headroom I need. With it pegging artificially soon now I'm getting fairly high MAF readings and it's pulling a lot of timing. Truth be told with the high IATs the truck doesn't seem to want much, if any, more.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  6. #96
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    Have you actually pulled 512g/s through the MAF yet or is this just a projected problem? Your MAF curve has been beat up pretty bad in the low and mid ranges frequencies but the higher frequencies look very smooth... which makes me think you're just curve fitting those higher values.

  7. #97
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    Yep, the upper end of what I logged was requiring me to copy/paste with multiply in the .2 range, so I just applied that to all the cells I couldn't hit. Ya know, I have yet to do a calc.vet after actually plugging those fictitious values in. I probably ought to rescale first, then try to clean it all up. I'll admit I SUCK at making things smooth when I try to plug in the new data and blend it. At this point, I feel good about delineating the tip in stumble from any VE/MAF tuning.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  8. #98
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    Quote Originally Posted by Supercharged111 View Post
    I probably ought to rescale first, then try to clean it all up.
    Yes, well considering you're using ASA data (which is meant for 4bar fuel pressure) and you're running 3.5bar fuel pressure... you probably should rescale.

  9. #99
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    Don't forget that I left the IFR geared for 3.5 bar and bank assignments for the GenI. I picked up an aluminum LS motor yesterday so maybe I can steal its 4 bar regulator and toss it on the truck if it fits.
    1998 GMC Sierra K1500 5.7/4L80E, longtubes, 411 w/COS 5, marine cam/intake, Whipple. 91 octane at 6000'.
    1997 GMC Sierra K3500 7.4/4L80E, 411 w/COS 3, Whipple, small cam.
    2004 Corvette Z06 with longtubes.

  10. #100
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    You really like doing things the hard way... don't you?

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