Electrical load problem

Small Block Mopar Engine

  1. Sinister.

    Sinister. Well-Known Member

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    I'm not 100% sure where this goes...
    Okay. Here's the info.
    1972 Dodge Dart Swinger
    318 (mild build) / 727 stock (~1000 miles)
    New Alternator, New voltage regulator, fairly new battery, new electronic ignition module.

    Start car, runs drives great.
    Turn on headlights at idle with low heater fan... dies.
    Anytime I put a heavy electrical load on it, it dies.
    I've idled it up some and this helped but with high beams, low-high fan, it dies.
    I've tried this with my fathers truck... high beams, high fan, brake lights, dome light... at idle.... doesn't even phase it.

    Any suggestions/tests I can do for more information?
     
  2. Sinister.

    Sinister. Well-Known Member

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    To vague or have i stumped everybody?
     
  3. 67gtx

    67gtx Well-Known Member

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    Do you have a voltage or amp guage hooked up? ANd what to they say.
     
  4. rumblefish360

    rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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    What size amp Alt. is in it now.

    The older cars didn't have a great system when new and what you describe I consider normal. It shouldn't be so much as to kill a running engine though.

    I am currently useing a '79 engine in my '74 Duster. The engine is a complete swap in full meaning a '79 100 amp Alt. is being used. If you go this route, the fuseable link may burn out. I had a wire fire at the walls bulk head connector. (Crap contact) I just jumped it with a larger gauge wire. (About 3 times the size ruffly speaking.)
     
  5. RedFish

    RedFish Well-Known Member

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    Sounds like a bad altenater to me. Part store reman'd aren't always good ones.
     
  6. green1

    green1 Well-Known Member

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    Voltmeter check the charging circuit.
     
  7. jd_physicist

    jd_physicist Well-Known Member

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    What's your voltage at the coil while running? I'm wondering if your ignition resistor is going bad and dropping too much voltage, leading to weak spark under electrical load.
     
  8. moper

    moper Well-Known Member

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    The electrical system in these cars is old design. Fuses, no buss or relays for the higher draw stuff... I would check the bulkhead connector for cruddy connections, and the fusible link wire too. You need to run about 9volts for the stock electronic ignition to fire, about 6 with points. So if you're really that low you have a serious problem. If all the stuff is new and functioning then you need to check the wires...
     
  9. Eric_S68

    Eric_S68 Well-Known Member

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    Follow the output wire from the alternator to the fire wall pass thru. I'd bet a beer that you have a poor connection, Either at the firewall. or somewhere between the alt and firewall. Look close at the outside of the plastic on the firewall connector, there usually melted slighty cause mopar used too small a wire guage. I would just run a nice 10 guage wire to some point inside car, if memory serves it runs to the amp guage.
    Also check for Bad Grounds. that's a common culprit too. Just cause you cant see it dosent mean maybe your negative batt cable is bad.

    It a cheap fix i'll tell ya that.
     
  10. Sinister.

    Sinister. Well-Known Member

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    amp gauge
    after initial recharge from cranking it shows just positive of 0.

    While running the battery runs at 14.5V

    I believe it's a 100 amp.

    Checking at the ballast, to the coil 5.4v with no load. Was going to check with a load but realized i can't because my headlights arn't installed. It's at 4.68v fully loaded minus headlights lol....


    after temporarily putting headlights back on it dives into the low 4's high 3's as it dies.
     
  11. MOPARJ

    MOPARJ What can I upgrade now?

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    I had a similar issue after putting a new ballast resistor on my 73 Duster.

    I tried swaping everything with extra parts I had to cure the issue and all wires looked great. I eventually swapped the old, but functioning resistor back in. The problem went away.

    I am assuming that is was just a crappy replacement resistor, which wasnt well built.
     
  12. Sinister.

    Sinister. Well-Known Member

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    my ballast seems to have the right resistances... 5 ohms to coil, 1.5 ohms on bottom
     
  13. 67gtx

    67gtx Well-Known Member

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    Well we had a problem with the 70 Dart. Not enough amps to drive the car.

    Fans 60 amps
    fuel pump 8-25
    MSD 8 ( need min. 11+ volts to start the car w/MSD, less than
    that is just turns the engine and doesn't start)
    Radio 10
    Headlights 15
    Guages 5
    Brake lights 10

    ALternator Stock Max. 80-90 idle 35-45 if your lucky

    Do the math. Stock will not work for us!

    So we bought a aftermarket alternator 155 amp idle 90
    Problem fixed.
     
  14. jd_physicist

    jd_physicist Well-Known Member

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    I don't have a running older mopar to check at the moment, but that sounds fairly low. Where were you holding the ground when you checked the coil voltage?

    I'd start with grounds. How does your engine to body ground look? Your engine to negative battery terminal? I assume you have an electronic ignition system on there...is it grounded well?
     
  15. godfatherofchry

    godfatherofchry Legandary Member Legendary Member

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    I agree. and I always ad extra grounds.
     
  16. Sinister.

    Sinister. Well-Known Member

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    Was on negative terminal.

    Eng - body... great.
    Eng - neg... pretty good.
    electronic ignition... yup.

    If i remember right.. resistance from neg terminal to body was like .1 or .2 ohms
     
  17. Sinister.

    Sinister. Well-Known Member

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    What tests should I run?
     
  18. Sinister.

    Sinister. Well-Known Member

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    I'm going to get my alternator tested on monday. After putting a different voltage regulator on that was charging at 17v, it still died.
     
  19. Sinister.

    Sinister. Well-Known Member

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    Alternator tested out fine. I'm going to go ahead and clean up the battery terminals and check all of my grounds again. Then it's back to body work.
     
  20. Sinister.

    Sinister. Well-Known Member

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    Further testing reveals...
    Alternator is putting out about 5 amps unloaded.
    Field wire amperage is erratic.
    Car is now dieing with just headlights on, in drive. Even after running a new ground for the alternator and battery.

    I really have no idea where to go from here.
     
  21. Eric_S68

    Eric_S68 Well-Known Member

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    I saw 17 Volts now your over charging... Top limit of any mechanics scale is 16.5 Volts. I still get the feeling that your alternator output is not reaching the fuse box under Dash.



    QUOTE=Sinister.;618158]Further . testing reveals...
    Alternator is putting out about 5 amps unloaded.
    Field wire amperage is erratic.
    Car is now dieing with just headlights on, in drive. Even after running a new ground for the alternator and battery.

    I really have no idea where to go from here.[/QUOTE]
     
  22. RedFish

    RedFish Well-Known Member

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    if the altenator tests good the battery is bad. Has to be one or the other.
    I've seen cases where I could put on jumper cable start the car and drive it , but to just step on the brake lights would cause the engine to skip then die. I had to start in neutral and use the hand brake to get it to my bay.
     
  23. Sinister.

    Sinister. Well-Known Member

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    The bulkhead connector looks fine. I looked up under the dash and saw that the black wire to the ammeter was butt spliced. After pulling my instrument panel to get better access to it (needed to change fuel and temp gauges anyways) I gave it a little tug and it came apart. I traced the wire back, found a junction and replace it. Unfortunately this didn't help... A little bit later I was looking at my ballast resistor and gave one of the wires a jiggle and it fell out. Sooo I put a new end on those... still didn't help. Got my battery tested... it's good... After looking online I found that my alternator is actually a 78 amp but that should be more than enough to let my car run in drive with the headlights on...
     
  24. jd_physicist

    jd_physicist Well-Known Member

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    The ignition system should take less than 10 amps. Headlamps, about another ten amps on high beams.

    How'd you fix that butt splice? Solder and shrink wrap is the only way to go--you have full charging current going through that link.

    Speaking of that...what was the OEM alternator output? If it was less than 78 amps, then I would run a proper sized charging wire, with fusible link, from the alt. output directly to the battery pos. terminal. Your factory wiring in perfect condition might be dangerously small for your alternator.

    You don't want to burn that car up...especially not with you inside.
     
  25. jd_physicist

    jd_physicist Well-Known Member

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    Okay, I don't have a service manual for 1972 around me, but according to Allpar.com's 1972 Dart info, the V8 cars had 41 amp alternators.

    I would definitely modify the charging circuit to handle the increased output, and definitely include an appropriate fusible link. I would not trust the factory bulkhead connector, ammeter, or wiring with an alternator that can put out almost twice the original alternator's current.
     
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