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Thread: MFI Sporadic Run

  1. 08-02-2013, 02:54 AM #1
    50/50
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    MFI Sporadic Run

    Have a sporadic problem with a 2,2S that stumbles/backfires along when started, then runs strong after warming up. And after turning off and restarting, while still warm, repeats the same condition.
    This condition started after adding 5 gallons of Cam 2 (recommended by 2 mechanics) to 93 octane Sunoco. I am thinking that maybe some residue/contaminents
    are sporadically causing fuel delivery problems. Fuel filter is relatively new but I am going to change it. Electrical/spark appears to be OK. Any thoughts?
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  2. 08-02-2013, 04:04 AM #2
    RSTarga
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    what is Cam2?
    David

    '73 S Targa #0830 2.7 MFI rebuilt to RS specs
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  3. 08-02-2013, 04:51 AM #3
    mac73s
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    Cam2 is an over-the-counter hi-octane racing fuel

    Quote Originally Posted by RSTarga View Post
    what is Cam2?
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  4. 08-02-2013, 05:24 AM #4
    Mr9146
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    Bad injector(s)
    -Marco
    SReg. #778 OGrp: #8 RGrp: #---
    TLG Auto: Website
    Searching for engine #907495 and gearbox 902/1 #229687
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  5. 08-02-2013, 10:10 AM #5
    Flieger
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    Is your MFI thermostat working correctly? Hose from the heat exchanger in good condition, etc.
    1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
    Early 911S Registry Member #425
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  6. 08-02-2013, 03:13 PM #6
    50/50
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    "bad injectors"= clogged? Doesn't explain how it will run very strong for 30 plus minutes.
    MFI thermostat was removed by previous owner during rebuild. Never effected operation except for cold start ups. Also these episodes have been with a warm engine on 80dg F day.
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  7. 08-02-2013, 03:22 PM #7
    Mr9146
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    Quote Originally Posted by 50/50 View Post
    "bad injectors"= clogged? Doesn't explain how it will run very strong for 30 plus minutes.
    MFI thermostat was removed by previous owner during rebuild. Never effected operation except for cold start ups. Also these episodes have been with a warm engine on 80dg F day.
    Yes it does.

    Injectors spray well enough to run at speed, but since they're bad they drip, piss, and spit so they don't hold pressure for restart/cold start or low RPM (idle) running. Take 'em out for a good cleaning and check opening pressures and spray pattern. Chances are you have one or more bad injectors. Replace all 6 for magic.
    -Marco
    SReg. #778 OGrp: #8 RGrp: #---
    TLG Auto: Website
    Searching for engine #907495 and gearbox 902/1 #229687
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  8. 08-02-2013, 08:14 PM #8
    Flieger
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    If you don't have the thermostat on there then your mixture settings are a compromise between warm running and cold running. Sounds like yours is more towards warm running. I know my car runs better on warm sunny,days than cool, humid days (hesitation, backfiring). It doesn't have the thermostat. But you say you get this problem on warm days so I don't know what to say then.
    1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
    Early 911S Registry Member #425
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  9. 08-03-2013, 11:28 AM #9
    edmayo
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    How much compression are you running that you need race gas? Basically the purpose of the removed thermostat is to compensate for the exact condition you describe, altho this can be caused by a multitude of problems, maybe the points have closed up??? all kinds of possibilities here! I find it hard to believe that this was started by running different fuel, something else is going on.
    Early S Registry member #90
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