'79 308 running rough and tach not working | FerrariChat
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'79 308 running rough and tach not working

Discussion in 'Technical Q&A' started by kdf398, Feb 28, 2005.

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  1. kdf398

    kdf398 Formula Junior
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    Nov 11, 2003
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    Keith
    #1 kdf398, Feb 28, 2005
    Hello everyone,

    I have searched the archives and am still in need of some assistance. Recently, my '79 308 suddenly lost power while it was sitting in the garage warming up. In addition, the tach stopped working. Upon examination, it appeared that the forward bank was not firing. I thought I had traced the problem to the coils. However, I changed out the coils and the problem remains (no forward bank and no tach).

    The spark plug wires and coil wires and distributors are all fine. I am not familar with the ballast resistors attached to the coils. Could these be the source of the problem? If so, how do you check them and fix them? Is there a relay that could be causing this problem?

    Thanks in advance for your help
     
  2. f355spider

    f355spider F1 World Champ
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    #2 f355spider, Feb 28, 2005
    Have you checked the coil wire for continuity between the coil and the center (inside) the distributor cap? Also, inspect the inside of the distributor cap...sometimes the button inside the center of it can stick (depressed) losing continuity. Or the button can wear out...you can order a replacement button and spring.
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #3 Steve Magnusson, Feb 28, 2005
    No relays involved in the later '78~'79 308 ignition.

    One easy thing to do is to disconnect the wiring from one terminal of each ballast resistor and then measure the DC resistance between the two terminals of each ballast resistor. I don't know the specified resistance value, but they should both be just a couple~few ohms resistance and they should be quasi-equal (i.e., a high resistance, or an open circuit, would be bad).

    You can also just swap the ballast resistors and see if the "problem" moves to the other bank.

    How did you determine the "distributors are all fine"? If it was a problem in the secondary wiring (dist cap, coil wire, coil button, etc.) I think the tach would still work (since the tach senses the primary coil current turning on and off), but if it's a problem in the primary side of things (ballast resistor bad, points not opening and closing properly, no +12V on the yellow coil wire, etc.) you'd get the symptom that you describe (no tach and no spark). Are you running R1 and R2 points, just R1 points, or something electronic?
     
  4. ham308

    ham308 Formula Junior

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    #4 ham308, Feb 28, 2005
    If the tacho is also not working then its a great clue that the points or optical trigger or whatever is not producing the signal for the coil. Mine did this when the connection plug in the wire from the Crane's optical trigger to the coil was faulty.
     
  5. Sophia

    Sophia Formula Junior

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    #5 Sophia, Feb 28, 2005
  6. kdf398

    kdf398 Formula Junior
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    #6 kdf398, Feb 28, 2005
    Thanks for the help everyone. Steve, I am running R1 and R2 points. I think they are okay because I visually inspected them. Also, I had the distributors rebuilt with new points, rotor and condensor about two thousand miles ago and have had no problems. I will attempt to check the ballast resistors as you described.

    Keith
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #7 Steve Magnusson, Feb 28, 2005
    OK Keith -- If you visually verified that both points sets are opening & closing in a reasonable manner (and the ballast resistor checks out as OK) about the only other thing that comes to mind is a shorted condensor. Just another possible thought, but like all problems all you can do is start cutting the branches off of the tree until you find the problem -- let us know how it works out.
     
  8. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
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    #8 Steve King, Feb 28, 2005
    I would recheck the points. That is the weakest part of the system and why most people get rid of them. Put a dwell meter on that dizzy and crank over the engine. If the dwell meter gets a reading as you crank then the points are ok. Should see a dwell of 39 degrees +/-3. I would suspect that they are not working and that is why the tach doesn't work either. As for the ballest resistor just jumper the resistor out and see if the car will start. If it does then the resistor is "open" and needs to be replaced. You can let the car run for a few minutes with this jumpered out and it won't hurt anything. The other thing is to just switch the coil wires and see if the bad bank runs.
     

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