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Thread: MFI - Surging at Part Throttle - 911E '71

  1. 06-13-2020, 10:25 AM #1
    webco
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    MFI - Surging at Part Throttle - 911E '71

    I know there are a million threads on MFI but I couldn't find one that describes the issues I'm having. I have a '71 911E that I restored a few years ago. MFI was redone by Gus Pfister. Bosch CDI box redone by Ashcroft. The car ran perfectly for over 2000 miles. Yesterday I went on a 1 hour drive and it ran fine but started to stumble a bit after I got off the highway. When I headed home after several hours, it was stumbling and popping a bit on startup. But, ran fine for 30 minutes or so, did a few stumbles, then completely died. I pulled over, turned off the key, started it again and it ran perfectly for a while - then same thing happened. I discovered that if I turned off the key when it was stumbling and then turned it back on, it would run fine for a while.
    So today I fired it up. Didn't drive it but warmed it up to near 180 degrees and discovered that as I revved it up to 1400, it would cut out, almost stall, then go back to idle. Likewise, when I held the revs at say 2500 and slowly let off, it would do the same thing once it dropped below 2000. Micro switch is set right. Where else should I be looking? Two separate problems or related? Seems like a weird coincidence if it's two separate problems. Any help appreciated!
    Thanks,
    Bill
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  2. 06-13-2020, 11:47 AM #2
    edmayo
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    When was the last time you checked the ignition point gap?
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  3. 06-13-2020, 01:35 PM #3
    webco
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    Quote Originally Posted by edmayo View Post
    When was the last time you checked the ignition point gap?
    Thanks - I set the points 2500 miles ago when I restored the car. Should be OK.
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  4. 06-13-2020, 05:34 PM #4
    NorthernThrux
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    Back off on the microswitch so it doesn’t engage and see what happens. It could be that your MFI speed relay has an intermittent fault.

    Ravi
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  5. 06-13-2020, 05:48 PM #5
    webco
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    Quote Originally Posted by NorthernThrux View Post
    Back off on the microswitch so it doesn’t engage and see what happens. It could be that your MFI speed relay has an intermittent fault.

    Ravi
    Thanks Ravi. Which one is the speed relay?
    Bill
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  6. 06-13-2020, 05:53 PM #6
    NorthernThrux
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    It is #5, the narrower of the 2 silver boxes on the electrical console on the left side of the engine bay.

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    Early 911S Registry # 2395
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  7. 06-13-2020, 08:21 PM #7
    eprnjp
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    I'm with Ed, recheck the point gap. Did you lube the contact when you set the gap. I've seen the contact destroy itself if not lubed properly.
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  8. 06-19-2020, 03:09 PM #8
    greens
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    After ignition checks I suggest you check the overflow check valve on your filter console before you touch the pump or other fuel system adjustments. My original one went south and the symptom was the car exhibited a lean condition. If your spark plugs look lean, I'd bet on that as an issue. They are available from Porsche
    Jim Lonsdale
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  9. 06-21-2020, 10:25 AM #9
    webco
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    Thanks Jim. Will do
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  10. 06-21-2020, 09:59 PM #10
    raspy2point2
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    I have had good luck with the pertronics ignition on the dizzy. no more points-seen too many break downs on R- gruppe drives with points. I put one on 18 years ago and never a problem. Chris
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