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512 BBi Flooding One Bank

Discussion in 'Boxers/TR/M' started by Teeter80, Jul 2, 2025.

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  1. Teeter80

    Teeter80 Rookie

    Nov 12, 2024
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    South Florida
    #1 Teeter80, Jul 2, 2025
    I recently removed the engine in a 512 BBi to replace the head gaskets. I reinstalled the engine and go to fire it up and found the right side bank was literally blowing fuel from the exhaust manifold. I removed the spark plugs from the right bank and found all the cylinders extremely flooded. I am not to familiar with the Bosch CIS and assume the issue is with the fuel distributor?
     
  2. turbo-joe

    turbo-joe F1 Veteran

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    #2 turbo-joe, Jul 2, 2025
    remove the injectors and look if they are spraying as soon as the ignition is on and engine not running
    also check the cold start valve if always spraying
     
  3. Teeter80

    Teeter80 Rookie

    Nov 12, 2024
    19
    South Florida
    #3 Teeter80, Jul 2, 2025
    All of the injectors on the right bank are spraying as soon as the fuel pump is activated. And they are spraying ALOT of fuel!!
     
  4. turbo-joe

    turbo-joe F1 Veteran

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    #4 turbo-joe, Jul 2, 2025
    then check the fuel distributor. may be the plate inside goes not in stop position back?
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    #5 Steve Magnusson, Jul 2, 2025
    +1 -- the plunger in the fuel distributor being stuck in the open position is a likely suspect. OP - Crack open (and then retighten) a fuel line on each bank to ensure that the fuel pressure is zero. Then just use a finger to manually deflect the airflow metering plate on each bank to compare their motion, feel, and return to the idle position (of the airflow metering plate and plunger).
     
  6. Newman

    Newman F1 World Champ
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    Dec 26, 2001
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    #6 Newman, Jul 2, 2025
    Make sure you hooked up the lines correctly at the fuel distributor. You may have crossed two.

    Meaning the supply, cold start and regulator lines.
     
    turbo-joe likes this.
  7. Teeter80

    Teeter80 Rookie

    Nov 12, 2024
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    South Florida
    #7 Teeter80, Jul 7, 2025
    I removed the fuel distributor and found the plunger stuck in the up/open position and does not want to return to the down/closed position with what seems to be excessive force. How easily should the plunger move?
     
  8. turbo-joe

    turbo-joe F1 Veteran

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    #8 turbo-joe, Jul 7, 2025
    very easy, you not need even 50 gram when the pump is not running.
    so is the plunger not moving in any direction? then could be because of all the chemical stuff in the fuel it is stuck. try to get it loose without much force. once moving I think it will be ok again.
    you removed the fuel distributor? so removed it from the case or took all in one part out?
    could you post some photos pelase
     
    Steve Magnusson likes this.
  9. EDoug

    EDoug Formula Junior

    Apr 19, 2005
    266
    Southern Florida
    #9 EDoug, Jul 10, 2025
    Teeter, not sure if you have the plunger unstuck yet, but assuming that your BBi FD is essentially the same as my '86 Testarossa, here are a couple of my Testarossa pics to help you visualize the plunger. It slides like a greased pig when normal and the WSM cautions not to let it fall out unintentionally. So that is how slippery it should be. EDoug


    Image Unavailable, Please Login

    Image Unavailable, Please Login
     
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  10. Teeter80

    Teeter80 Rookie

    Nov 12, 2024
    19
    South Florida
    #10 Teeter80, Jul 14, 2025 at 3:33 PM
    So it looks like sticky plunger came down to 110 octane leaded aviation fuel being used. After finding out what fuel was in the tank it all started to make sense. The fuel had the same properties as brake clean solvent. It evaporated extremely quick and offered no lubrication. I drained the fuel tank, removed both fuel distributors and cleaned & lubed the plungers. Put it all back together, put 93 gasoline in the tank and have hade zero issues since.
     
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  11. turbo-joe

    turbo-joe F1 Veteran

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    #11 turbo-joe, Jul 14, 2025 at 3:36 PM
    great that you find the problem
    now you may drive and enjoy :)
     

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