Uh oh...voltage crash and now won't turn over

Discussion in 'Electrical and Ignition' started by 67dartgtgo, Jun 17, 2018.

  1. 67dartgtgo

    67dartgtgo FABO Gold Member FABO Gold Member

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    Hi Guys,
    The other day I was out as a cruise night and noticed my voltage all of a sudden became erratic on the low side at idle. I was actually idling through the parking lot when the voltage dipped and caused a stumble and stall. At increased rpm the voltage recovered and all was good. Checked connections...all good. Got her home and put her to bed. Last night when heading out for test drive she ran ok but the voltage was a bit low @ 11 volts...always runs a solid 13. Again checked all connections, Alternator connections as well, changed vr because I just happened to have a new in the box one in the cabinet. All grounds are good. Battery voltage is 12.4. Now the starter won't even crank....like it's not getting any power at all. Ignition key to on and voltage gage @ 12 volts, key to start and voltage crash to 10 volts or maybe lower as that's the bottom range of the gage. Everything works with the key in the on position...lights etc. Fusible link appears good. HEI conversion for over 2 years. Car was running awesome prior to the other day.
    Thoughts?....you guys are the best by the way.
     
  2. magnumdart

    magnumdart You in a heap of trouble boy.

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    I think the first thing I would do is charge the battery for a couple hours, then see if it will crank.
     
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    • 67Dart273

      67Dart273 Well-Known Member

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      Agree, I would guess at this point the battery is dead

      If "13" is an accurate reading even that is low. A proper "low to medium" cruise RPM with a normalized/ charged battery should run nominal 14

      Are you still running the original style altlernator/ regulator? That is the grounded field / one field connection?

      If so, monitor battery voltage, disconnect the field wire, and clip the alternator field over to a 12V source, such as the starter relay stud. Then slowly bring up RPM and see if the voltage comes up
       
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      • TrailBeast

        TrailBeast Slightly Twisted Member

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        Might want to jumper it at the starter relay and see what it does. (some sparks at the relay terminals is normal)
        Also check that engine harness connector at the rear passenger side of your engine if you have that connector.
        Those connections in that connector can get sketchy and cause charging issue's.


        The fact that the voltage drops when you try to start it but it doesn't crank points to low battery amps, or a possible ignition switch/relay/starter problem.

        Of course this is just basic first steps to diagnose.

        You want to connect "Battery" to "Solenoid" to test for cranking.
        This will bypass the entire key switch and ignition system and should crank the engine.
        Let us know what you find when doing this.

        90-StarterSolenoid.jpg
         
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        • Paladin06

          Paladin06 FABO Gold Member FABO Gold Member

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          This brings back some memories for me. See my thread “voltage drop at ballast resistor “. Lots of good info from FABO. Good luck.
           
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          • 67dartgtgo

            67dartgtgo FABO Gold Member FABO Gold Member

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            Will try all the above.
            I have the 2 wire connector and post alternator. Green and blue from the vr to the contacts. Alt housing is also grounded to the block. Never had an issue. My next thoughts were trailbeasts in that order but i'll def make sure of the battery condition prior. Working today and tomorrow so tomorrow night or Tuesday will be the soonest I can get to it. Will put the charger on it tonight.
             
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            • 67Dart273

              67Dart273 Well-Known Member

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              So you have converted to the newer VR and isolated field alternator? What year is the car??
               
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              • 67dartgtgo

                67dartgtgo FABO Gold Member FABO Gold Member

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                It's a 67 with a 98 5.9 magnum but was this way when I bought it. Have never had a problem with it. The ignition switch is the original and a bit loose but no more than others I've seen.
                Have also done the MAD upgrade...
                 
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                • Paladin06

                  Paladin06 FABO Gold Member FABO Gold Member

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                  The ignition harness was my Big killer.
                   
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                  • 67Dart273

                    67Dart273 Well-Known Member

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                    OK but you are not answering the important question. do you have the 67 style alternator or the isolated field (70/ later) with the flat electronic regulator? Or what else?

                    Cannot offer much help until we know what you have
                     
                  • 67dartgtgo

                    67dartgtgo FABO Gold Member FABO Gold Member

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                    Yes of course... I have the flat electronic vr, alternator has the post and 2 spade terminals. The vr blue and green wires to the alt field spade connections. All wiring came updated on this circuit when purchased.
                    I think that's it?
                     
                  • 67Dart273

                    67Dart273 Well-Known Member

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                    OK. In that case your "quick test" needs to be a bit different. You can test this several ways, which will, depending, test the alternator, and or the field wiring as well.

                    1....Charge the battery. No sense doing anything without this. You can "dirty quick" test the battery after you get it charged by jumpering the starter relay as shown in the posts above. If it cranks nice and fast, you are OK

                    2....Unhook the GREEN field wire at the alternator. Clip that field terminal to ground. Now turn the key to "run" and measure voltage at the BLUE alternator field terminal. This should be very close to "same as battery" and at least 12V or more

                    3....In subdued light, if possible, unconnect and reconnect your clip on the other alternator field. You should see a small spark each time, which shows the alternator field is drawing current

                    4....Start the engine, and with a meter on the battery, slowly bring up RPM. Don't let it climb above 16V but see if it does climb

                    5...If the voltage doesn't climb much or at all, shift your multimeter to the alternator big output stud, and again, bring up RPM. If the stud voltage goes way high, then there is an open/ poor connection between alternator and battery "the charge line."

                    6...If voltage does NOT climb, the alternator is not charging. First thing to do is pull it off and remove brushes and inspect. They may be worn, broken, greasy, stuck etc. If they appear OK reinstall the brushes and check resistance between the field terminals. Should be a low reading "a couple or 4" ohms.

                    If field is open, replace alternator. If brushes are bad you MAY be able to buy a set. Take the old ones with you. Otherwise, if the tests above showed no charge, replace the alternator

                    =================================

                    7......If in the above tests the voltage DID climb at the battery, now we need to test the field wiring. To do that, reconnect your field wires, and disconnect the VR connector. Make SURE the VR is firmly mounted and GROUNDED. Remove, scrape around the bolt holes, and remount with star lock washers.

                    Push / pull the VR connector several times to "feel" for tightness and to scrub the terminals. Inspect with a light are they clean? Reinstall, see if it charges

                    If not

                    8.........We are again going to jumper the field "full field" as in earlier tests, this time using the VR wiring. Remove the BLUE field terminal at the alternator, and clip that field alternator terminal to ground. Now devise a way to jumper across the to VR connector terminals, machine screws, etc.

                    9....Again monitor battery, start and run, bring up RPM. Voltage should climb. If not and if the alternator worked in earlier tests, replace the VR
                     
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                    • Murray

                      Murray FABO Gold Member FABO Gold Member

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                      Might be alternator brushes going bad.
                       
                    • 67dartgtgo

                      67dartgtgo FABO Gold Member FABO Gold Member

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                      I think this is exactly what I need. Thank you 67dart273.
                      I'll let you know how I make out.
                       
                    • 67dartgtgo

                      67dartgtgo FABO Gold Member FABO Gold Member

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                      Ok gang. Finally able to wrap this up. Followed 67dart273 testing guidelines and found to be a bad alternator. Oh and the reason it wouldn’t turn over was a faulty neutral switch. Fixed that too.
                      Took me a couple days of nonexistent time but we’ll worth it.
                      Thank you guys, as always it’s nice to be able to have this kind of support when you’re scratching your head.