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Thread: '71 911E MFI starts cold but won't start when warm

  1. #1
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    '71 911E MFI starts cold but won't start when warm

    My '71 911E with MFI will start ok (not great right now) when it is cold. However after it is warm it won't restart. Have to let it sit until it is pretty much cold again. We have spark so pretty sure it is a fuel issue. It keeps running once it is started. Will start warm with a direct spray of starter fluid. Runs well otherwsie.

    Car has 86k miles and MFI has not been rebuilt that I know of.

    Still trying to solve a fuel smell problem with this car. Any suggestions greatly appreciated!

    1971 911E Targa Albert Blue
    '91 Nissan Figaro
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    Last edited by 71Targa; 12-29-2020 at 08:38 AM.

  2. #2
    Moderator Chuck Miller's Avatar
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    Please tell us your starting procedure for cold start and hot start...

    If everything is working starting procedure should be:

    -Cold start should be hand throttle all the way up, no accelerator peddle, turn the key...

    - Hot start should be hand throttle down/off, accelerator peddle floored, turn the key....

    These cars get cold in a hurry... so even after a lot of hot driving I've found I'd had to go to the second procedure after only about 15 to 20 minutes...

    Hope this helps,
    cm
    Chuck Miller
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  3. #3
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    Yes, that is what I do. Starting has sometimes been finicky prior to this, but have never not been able to start it.

    I added more info to the post. It will start hot with a direct spray of starter fluid, though not easily. Car has 86k miles and MFI has not been rebuilt that I know of. I wonder if the fuel smell could be related to the MFI. The smell is in the upper left area of the engine compartment. Just changed hoses for a second time. Could an issue with MFI allow fuel to leak and smell to escape the air intake? Could something be going on with the MFI when hot that isn't allowing fuel at startup? Once running it runs fine so fuel isn't cut off permanently when warm.

    Thanks for the response!

  4. #4
    What hoses have you changed? Is the energizing wire attached to the solenoid on top of the fuel filter housing? Are the spray bores in the air cleaner housing open,,,has the aircleaner housing been painted recently? Is the cold start supply hose attached to the aircleaner? Last time ignition points and timing were checked? So at one time in your ownership it started okay hot,,,has anything been done to the engine since then? like replating linkage parts. And like Chuck mentioned,,,,when you hot start you are opening the throttles? Has the gasoline supply changed in your area? higher alcohol content? The spark plugs are how old? All of these questions and many others need to be asked to try and solve a problem from miles away and over the internet.
    Early S Registry member #90
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  5. #5
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    Hi: I will have to check some of these with the mechanic who is off this week, and the car is at his shop so I can't look. All hoses have recently been changed. I'm using ethanol free gas. The lower section of the air cleaner housing was recently powder coated. Haven't done anything to the engine. When hot starting pedal to the floor with hand throttle off. Plugs are quite new. Thank you for your reply and insight.

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    Mechanic confirmed the energizing wire is attached to the solenoid. Will have to double check the spray bores - only the bottom was painted - wouldn't that impact only cold start? Cold supply hose is attached. He said it is fuel starvation, it runs fine cold or hot when running, so he doesn't think it is the ignition or timing.

  7. #7
    Senior Member NorthernThrux's Avatar
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    Energizing wire to the solenoid is not enough. The fuel filter housing assembly needs to be grounded or the solenoid wire does nothing. Use an ohm meter and check you have zero ohms between the solenoid body and chassis ground.

    Ravi
    Early 911S Registry # 2395
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  8. #8
    We're going to have to take this in small steps. You said it once started fine hot,,,,something changed, was it after the powder painting? Start with a simple test, remove the wire from the cold start solenoid, attach a simple 12v. tester to the removed wire ground the tester tip, crank the engine (cold test) does the tester light for about 2 seconds? If yes repeat test with warm engine, does it still light? Answer this and then we'll go from there.
    Early S Registry member #90
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  9. #9
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    Definitely a fuel starvation issue. The check valve in the fuel filter was not working. Replaced that and we were able to get it to start hot, but after running awhile it started to lose fuel. We are going to replace the fuel filter, the mechanic said he is seeing some debris in the fuel. We replaced all the fuel lines recently (for a second time), perhaps deteriorating fuel lines have fouled things up. I think we need to have the MFI pump rebuilt. It has a brand new fuel pump at the front.

  10. #10
    As always check the in tank filter sock. That is often the culprit as they tend to be forgotten about.
    Early S Registry member #90
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