OK why? Blowing ignition condensers

Discussion in 'Sparky's corner' started by BigTodd, May 20, 2017.

  1. BigTodd

    BigTodd Well-Known Member

    Stock 350, automatic
    Stock points/condenser dizzy

    OK Why is this happening? The coil resister wire wore out in my 72 350. This was the main cause for my cars poor idle, dying at stop signs and such. I was only getting 2.3 volts to the + side of the coil. I took off the bulkhead connection and replaced the resister wire with some new 14 gauge wire and a 1.8 ohm ballast resistor. I now have 5.5 volts at the + coil connection. The car now runs great, with one exception I have blown 3 condensers. Each condenser has lasted for about 100 miles then sputter sputter, cough dead. Put in a new condenser runs like champ. WTF

    I have checked the voltage at the + coil terminal with the key on, not cranking or running = 5.5 volts, volts while cranking = 12 volts (Starter lead spliced into the new 14 gauge wire just before the coil). Voltage on the + coil terminal while running = around 9.3 volts. This all looks to be dead on according to the shop manual ignition specs.

    I did have a new coil installed, a BWD E30 which I measured the primary winding's across the +/- coil terminals and noticed I was getting 1.2 ohms instead of the 1.5 ohms I expected. I then looked at the old coil and did have 1.5 ohms across the +/- terminals. So I swapped the old stock coil back onto the engine. car fires up and runs great, but for how long is the question. Has anyone else ran into this problem, having the correct voltages but still burning up the condensers? I've tried AC Delco, BWD stock and heavy duty condensers still no luck.

    I've already bought a HEI conversion kit for my stock Dizzy but I'm concerned to put it in because of this electrical issue. Thoughts or recommendations...
     
  2. BigTodd

    BigTodd Well-Known Member

    Anybody ?
     
  3. telriv

    telriv Founders Club Member

    Probably condensers made of chinesium.
     
    SteeveeDee likes this.
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I would double check ALL of my grounds. Not much demand for condensers anymore, so the ones you are buying may be old, or cheaply made.
     
    SteeveeDee likes this.
  5. gsgnnut

    gsgnnut Well-Known Member

    Time to switch to petronics or hei. My guess is the ballast resistor may be suspect. Shouldn't have more than 6v at coil except during cranking.
     
  6. BigTodd

    BigTodd Well-Known Member

    Larry, the grounds could possible the issue, but I'm wondering how the distributor could not be properly grounded. The distributor body is installed physically into the aluminium timing cover, the internal plates of the distributor are all steel and come in contact with the distributor body. I don't see how the breaker plate can be electrically isolated from the ground provided by the engine block. I have seen on older distributors a small grounding wire from the dizzy body to the breaker plate. Could the aluminium timing cover be that poor of a conductor that an additional ground strap should be connected to the distributor?
     
    Last edited: May 21, 2017
  7. telriv

    telriv Founders Club Member

    ALL distributors need that small ground wire you're talking about. The breaker plate IS ISOLATED from the rest of the distributor, that's why there is the ground wire.
     
  8. BigTodd

    BigTodd Well-Known Member

    So I took my distributor out today and gave it a good once over. Checked the ground cable from the vacuum advance to the breaker plate, nice and tight, 0.00 ohm's. I also cleaned up the dizzy base that slides down into the timing cover, cleaned the bolt and retainer clip. I also cleaned off all the paint from the timing cover where the dizzy slides in to improve any grounding. Checked all of the dizzy parts with the VOM all checked 0.00 ohm's.

    While inspecting I found the vacuum advance diaphragm was bad, would not move the plate when I used the mity vac. Swapped in a spare and took the car out for a test drive. Wow got a lot of my power back. Now let's hope the cleanup of the dizzy grounding points helps with the condenser issue.
     

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