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1980 Diplomat ignition trouble

Interior and Electrical

  1. SlantSixSullivan

    SlantSixSullivan Well-Known Member

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    Here's the scenario: About a month ago I had new exhaust put on my Diplomat. The catalytic converters were done away with and the back of the head where the EGR tube goes in was sealed off. Ever since then, the car has been shutting down. This normally only happens when I am approaching a stop sign/light. I know I have good fuel. I have a brand new carb on it. I used an ignition test light to determine the spark is intermittent and weak. I checked the cheap and simple stuff first. Ballast resistor, cap, rotor, plugs and wires, voltage regulator, ECU, ignition switch, plus the distributor and pickup coil. I have replaced every part listed above and the problem still persists. I did find a ground wire which appeared to be chewed by a mouse. Fixed that and still shuts down. What am I missing? Oh, by the way, all the power in this car runs through the ampmeter. It works as it should too.
     
  2. Joe12459

    Joe12459 Well-Known Member

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    Could be the ignition coil, but if it happened right after the exhaust work, I'm more inclined to think the wiring got disrupted somewhere. I would start at the bulkhead connector, and trace all of the wiring to the components it connects to. Look for broken or pinched wiring, loose or corroded connectors, etc.
     
  3. SlantSixSullivan

    SlantSixSullivan Well-Known Member

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    I've done the ignition coil too. I cleaned every terminal at the bulkhead connector. I've unwrapped MOST of the wiring to check for burnt or separated wires but not ALL the wiring
     
  4. Joe12459

    Joe12459 Well-Known Member

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    Wow, that is odd. I still can't help but believe the wiring got disrupted somewhere. Is it possible a wire got stretched and broke inside the insulation? I've had this happen before, and only found it by pulling on the wires. I would start by testing the voltage at the bulkhead connector ignition + terminals with the car running, and continue to test voltages until you find a drop. If you don't see a voltage drop on the positive side, check the grounds the same way.
     
  5. BudW

    BudW Moderator Staff Member

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    The exhaust work would not have caused any of these problems – unless something was removed and not reinstalled (a possibility, but not likely).

    There are two and engine ground wires.
    One is the large from the battery.
    There is also one from rear of engine to passenger side of firewall. This one is normally braided wire and many times is left loose or not reinstalled after engine repairs.

    Next is the ECU needs a good ground. It is grounded by the two mounting bolts – which are designed to scrape off the paint when tightening them.
    Every so often, on our older cars, rust or corrosion develops under those bolts allowing the ECU to lose a good ground. Sometimes removing each ECU bolts and giving each a good wire brushing and also taking a piece of sandpaper around each bolt hole does the trick.
    In some rusty areas – a person might need to run a jumper wire from ECU to the main ground strap (passenger side firewall).

    Now grounding issues set aside for now, another possible issue is the distributor pickup coil is a likely suspect - for they can act up intermittently.
    Finding a good replacement can be hard. It seems like the original red/black wire versions are far better than the replacement white/black wire versions.
    With that said, if yours is bad – anything has to be better . . .
    BudW