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Thread: MFI warm start issue

  1. #11
    don't think it's flooding (I think I'd smell it) - we don't have hot garages in Colorado for a couple more months, but I am going to rig something up so I can manually activate the enrichment - probably won't happen until the weekend, pretty busy with work and hopefully a spring ski day this week



    would appreciate any other input on this subject since replacing he overflow valve fixed this the last time
    73 911S Targa

  2. #12
    Quote Originally Posted by Flieger View Post
    I It is because the engine has cooled off enough to need enrichment, but has not cooled off enough that the temperature switch allows the cold start squirters to be activated.
    This is the correct answer.
    -Marco
    SReg. #778 OGrp: #8 RGrp: #---
    TLG Auto: Website
    Searching for engine #907495 and gearbox 902/1 #229687

  3. #13
    Rig a temporary jumper wire from a hot fuse at the 3 fuse panel at the relay board to the terminal of the cold start solenoid on top of the fuel filter. Then when the start problem occurs just momentarily touch the jumper to the fuse. That will squirt fuel through the squirt nozzles. (be careful to ONLY use momentary connections,,,,you can flood the hell out the engine quickly!!) This will tell you if your problem is lack of fuel squirt. Realize above 114 degree engine temp the cold start doesn't work anyway.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  4. #14
    member #1515
    Join Date
    Mar 2009
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    Ed,
    I've had a couple of 6.3 MB that have the same MFI system and suffer terribly from this problem. Ultimately someone came up with a thermo timer relay kit that over rides the hot shutoff of fuel and permits the enrichment circuit to operate at high temps. I think it gives 2 seconds or so of fuel when starting hot.
    Is this something that could be made for our cars?
    David

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

  5. #15
    I tried to get the problem to repeat on a warm day and now it is not exhibiting the problem

    However, I do have a misfire that I may be asking for help on

    I will carry a jumper wire with me just in case

    thanks to all
    73 911S Targa

  6. #16
    Quote Originally Posted by RSTarga View Post
    Ed,
    I've had a couple of 6.3 MB that have the same MFI system and suffer terribly from this problem. Ultimately someone came up with a thermo timer relay kit that over rides the hot shutoff of fuel and permits the enrichment circuit to operate at high temps. I think it gives 2 seconds or so of fuel when starting hot.
    Is this something that could be made for our cars?
    I don't know of any way to do that that doesn't involve a different resistance of the thermal time switch in the breather cover. I suppose the manual override button on the dash would be the comparable solution in this case. Although my car may sometimes crank a smidgen longer on a real hot start it is usually a matter of knowing how much to open the throttle to help it. I'm still convinced real gas would help a lot! I found myself in Ca. last week,,,,found out they DON"T have corn syrup in their gas!!!
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  7. #17
    Quote Originally Posted by edmayo View Post
    I don't know of any way to do that that doesn't involve a different resistance of the thermal time switch in the breather cover. I suppose the manual override button on the dash would be the comparable solution in this case. Although my car may sometimes crank a smidgen longer on a real hot start it is usually a matter of knowing how much to open the throttle to help it. I'm still convinced real gas would help a lot! I found myself in Ca. last week,,,,found out they DON"T have corn syrup in their gas!!!
    Where did you find non-ethanol petrol here? Except for the stations that sell 100 octane I have only seen E10.
    1971 911S, 2.7RS spec MFI engine, suspension mods, lightened
    Early 911S Registry Member #425

  8. #18
    Senior Member
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    VA
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    I bypassed the thermal time switch completly and made it a manual switch on the tunnel access pannel. Switch in forward position will activate the squirters when the starter is engaged. Starts like a champ every time. Will flood if the switch is in the forward position and the engine is hot. Will never start in this condition.

    Chris
    73 911 E

  9. #19
    Senior Member 2.5MFI's Avatar
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    [QUOTE=Boulder Bob;723934]
    As I understand it, the fuel system from the pump under the car to the injection pump needs to hold pressure and if it doesn't the injector pump will not deliver fuel to the injectors. Is this correct? I also understand that there is another check valve in the pump.

    The fuel system does not need to hold fuel pressure between the MFI pump and electric pump like the CIS system does when the engine is not running. The electric fuel pump in the MFI cars does this. Your check valve/connector (901 110 915 00) on the fuel filter console is the valve that keeps some fuel (not under pressure) in the lines between the MFI pump and filter console after the engine is turned off from draining back into the fuel tank. That valve/connector is the return fuel line back to the tank along with the electric fuel pump via a tee. If that check valve was leaking I think it would just add a few seconds of the electric fuel pump running to build it's pressure up. The actual fuel pressure relief valve is on the electric fuel pump.
    Mark Jung
    MFI Werks
    Early 911S Registry #972
    Carrera T w/LWB, MT, RWS, PCCB
    72 T 66 x 100 MFI Twin Plug Coupe
    R Gruppe #686

  10. #20
    Quote Originally Posted by Flieger View Post
    Where did you find non-ethanol petrol here? Except for the stations that sell 100 octane I have only seen E10.
    Well lets say that I never saw the sticker on the pump that we have indicating 10% ethanol. And a local told me you guys don't have ethanol!
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

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