Ignition gets no power during cranking - 77 GTB | FerrariChat

Ignition gets no power during cranking - 77 GTB

Discussion in '308/328' started by Nuvolari, Sep 19, 2018.

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  1. Nuvolari

    Nuvolari F1 Veteran
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    Rob C.
    #1 Nuvolari, Sep 19, 2018
    Today I decided to tackle something that has been going on for as long as I can remember (had the car 15 years already) but only recently have I clued into it and decided to do anything about it.

    Turns out that when I crank my 1977 308 GTB, the wires that feed the ignition coils and Pertronix units (this is a single distributor setup) do not receive any electrical power. The coils do get power when the key is in the run position but when the key is turned to the crank position the coils get no power. As such when I start the car it cranks over building engine speed and it then relies on those residual revolutions when the key is returned to the run position to fire the spark plugs and get the engine running. Not a huge deal but it means that starting takes a little more finesse and I don't believe it should be like that anyways so I want to get it fixed.

    Can anyone offer any insight as to the best way to approach this problem? I have already used a test light and ignition spark tester to confirm my diagnosis but I am not sure where to look for the best solution. The factory wiring diagram is incredibly difficult to follow so I need to rely on some old fashioned F-Chat wisdom to sort this issue out.
     
  2. BigTex

    BigTex Seven Time F1 World Champ
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    #2 BigTex, Sep 19, 2018
    wWell it almost sounds like the ignition switch itself has a bad terminal bond between 3 & 4 (if that's the switch markings).

    Sort the siring diagram as I would wager there is only ONE wire from the switch back to the engine compartment and those two terminals are meant to share it.
    Indicating to me a buss or connection on the switch has gone loose??

    There are some colorized versions of the diagram published, they do make it easier!!

    Not as familiar with Pertronics but maybe they only powered it to the run terminal and it needs to hit both as field wiring of that system?
     
  3. Ferraridoc

    Ferraridoc F1 World Champ
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    #3 Ferraridoc, Sep 19, 2018
    It's the switch. A new one costs about $100 - it's from a BMW 2002. Held on to the back of the lock with two screws - a fairly easy swap. It happened to my first Ferrari, a GT4, when I was showing it off to my mates - very embarrassing. ITMT, try turning the key so it just touches the start circuit - in my case, the coils stayed powered up and she fired up. That worked for me - if you turn the key too hard over, the voltage will go to zero again, but if you carefully turn it so it just activates the start circuit, the ign circuit might still have power.
     
  4. Nuvolari

    Nuvolari F1 Veteran
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    Rob C.
    #4 Nuvolari, Sep 20, 2018
    I'll definitely look into getting a new switch but will try and diagnose one first although most signs seem to point to it. Does anyone have leads on a new switch? It appears as though the BMW replacement part is closer to $300 and on back order everywhere.
     
  5. Milkshaker0007

    Milkshaker0007 Formula Junior

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    Paul
    #5 Milkshaker0007, Sep 20, 2018
  6. Nuvolari

    Nuvolari F1 Veteran
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    #6 Nuvolari, Sep 20, 2018
    Hiding in plain sight. Thank you Paul
     
  7. Nuvolari

    Nuvolari F1 Veteran
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    Rob C.
    #7 Nuvolari, Sep 20, 2018
    Final update: It was NOT the switch!

    I had my suspicions that the switch was indeed ok and with the generous help of two local F-Chatters we determined with 100% certainty that (at some time in the life of the car) the blue and black wires coming out of the back of the ignition switch were inverted. We swapped out the two wires and all was perfect even after running a number of tests to be sure that all is ok. No money spent just some time.

    I find it funny that with the multitude of people (including myself) who both drove and worked on my car over the past 15 plus years that nobody clued into the fact that both the ignition and fuel pumps were shutting off when the car was cranking. I guess we never stop learning with these cars.
     
    Milkshaker0007, ME308 and miketuason like this.
  8. miketuason

    miketuason F1 World Champ
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    #8 miketuason, Sep 21, 2018
    Great fix Rob!
     
    Nuvolari likes this.
  9. Steve King

    Steve King F1 Rookie

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    #9 Steve King, Sep 21, 2018
    When you did the pertronix conversion did they also change the coils and remove the large resistors and jumper the wires. When you turn the key to start you should get +12v at the coils , tach wire and the pertronix red wires. When you release the key to the run position you should still have voltage at these positions.
     
  10. Ferraridoc

    Ferraridoc F1 World Champ
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    #10 Ferraridoc, Sep 21, 2018
    D'OH!
     

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