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Thread: Hesitation or Surge?

  1. 03-01-2017, 10:50 AM #1
    wicks
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    Question Hesitation or Surge?

    Hi, my fresh in all respects CDI MFI 2.4s motor is developing a small hesitation or surge pulling through low RPMs at light throttle ranges. I can't tell if it is a hesitation or a surge, because either could cause what is happening. When it starts to do this push/pull thing, and if I leave the throttle as-is, the car ends up bucking so that the effect is compounded by the unavoidable pushing and pulling of the gas pedal due to the buck. It seems more like a hesitation than a surge. To correct, if I add throttle a lot, or let off completely, back to smooth and I can "start over". Once past 3.5K RPMs or so the problem does not exist.

    (MFI pump freshly benched MFIW
    CMA freshly done
    Fuel system (pump, filter, screens) freshly minted
    Disty redone and timing/dwell right

    Pointers? Or maybe there's a thread or two already on this - couldn't find.
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    1973 911s / 1994 964 Turbo / 1997 993c2
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  2. 03-01-2017, 03:46 PM #2
    edmayo
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    You say the timing is correct,,,,how did you set it, what are the readings you got? The pump is rebuilt ? but have there been any attempts to set the mixtures since installing? What is the length of the pump control rod? If you remove any of the throttle valve links is there any preload on them? Do you have an air/fuel ratio meter?
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  3. 03-01-2017, 07:25 PM #3
    Flieger
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    Kind of sounds similar to my car, except full throttle doesn't fix it, only revs do. Interested to see the responses.
    1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
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  4. 03-01-2017, 08:29 PM #4
    trdking
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    Hows the cap and rotor? Distributor play? If that is good it sounds like it is starving for fuel in the low end
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  5. 03-02-2017, 03:30 AM #5
    Frank Beck
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    What's a disty?
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  6. 03-02-2017, 03:38 AM #6
    edmayo
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    Frank, I believe it to be akin to a dizzy ??
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  7. 03-02-2017, 03:42 AM #7
    Frank Beck
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    What's a dizzy?


    I know "ditzy" describes a person who has no idea what they're doing. Is a disty or dizzy similar?
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  8. 03-02-2017, 04:49 AM #8
    edmayo
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    Frank, think of it as sort of an electrical merry-go-round. I know us old farts are easily confused by modern technical jargon !!
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  9. 03-02-2017, 07:38 AM #9
    wicks
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    You say the timing is correct,,,,how did you set it, what are the readings you got?

    >>>With gap then dwell meter, I think it was 38 degrees? Whatever was in the books. Oh and flywheel advance I have always had a problem. Even with fresh distributor rebuild I can only get to about 25 degrees advance. Like the springs are too tight or something. But car has been running fine without this problem until a couple weeks ago this small issue began to develop.

    The pump is rebuilt ? but have there been any attempts to set the mixtures since installing?

    >>> Yes just sorted by MFI werks.

    What is the length of the pump control rod?

    >>>I think it was 114 mm - whatever was in CMA. All rods are perfect no preload, nothing but perfectly synced and airflowing evenly.

    Do you have an air/fuel ratio meter?

    >>>This I don't have. Pump was set to factory spec flows on the bench...

    Hows the cap and rotor? Distributor play? If that is good it sounds like it is starving for fuel in the low end

    >>> Both new. No play. Dist just rebuilt by PK. I just tried changing to a new non-limiting rotor = no change.

    Yes disty=dizzy=ditsy.
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  10. 03-02-2017, 07:45 AM #10
    RSTarga
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    Are you in 5th at 3500 RPM at constant throttle or
    are you in ,say 3d at 3500 rpm constant throttle?
    If you accelerate through the gears and go through 3500 on the way to 6k or higher, do you have hesitation?
    David

    '73 S Targa #0830 2.7 MFI rebuilt to RS specs
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