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battery decharging

Discussion in 'Chevy Trucks' started by illday, Mar 9, 2004.

  1. illday

    illday Junior Member
    from RI
    Messages: 9

    I have a very old truck. It's a 1979 GMC Sierra with a 350.
    The truck has been great over the years and all of a sudden
    I' m having to jump start the truck 1 out of every 5 times.
    To try to fix the problem I've put a new battery in, and a new
    alternator. My next step will probably be to replace the
    positive and ground wires.
    Am I missing anything?
    The truck, beleive it or not still has a few years left. The engine
    is still strong and I'd hate to put it to rest because of a battery
  2. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Does the truck have any power accesories that could be drawing? ie: pw, pdl, stereo, alarm etc. etc.

    I'm assuming of course that you haven't left the dome light on or something... :D but seriously if you truck has one make sure the switch for the glove box light is still working! Had that one on an S15 Jimmy one time--glove box light stays on all night and that is it for the battery. My S15 pickup did the same thing with the hood light -mercury switch died. Didn't spot it until night time when all I could see was light coming out around the hood gaps!

    As far as electrical draw goes, there is a method that involves a test light between (I think, maybe someone can correct me here as electricity is not my best friend!) the ground cable and the negative on the battery.... I think you pull fuses or something until the light goes out and then you've isolated your general location?

    I think I'm close here but not certain. Hopefully someone more electrically inclined can help!

    This also assumes that the belt is tight and such.

    You think a '79 is old? Naw its just broken in!!! Lots more
    payup where that came from!!! lol
  3. The Boss

    The Boss 2000 Club Member
    Messages: 2,099

    The starter could be the problem also.:waving:
  4. JMR

    JMR Senior Member
    Messages: 567

    Is the battery actually completely discharged (dead) when it won't crank or is there plenty of battery power and it just won't crank. Big difference and each will lead to a different diagnostic direction.
  5. Dave_Dean

    Dave_Dean Junior Member
    Messages: 28

    I've removed the positive cable from the battery and placed a multi-meter between the cable and the + post on the battery to track electrical draws before. Sometimes it works and others it doesn't. Pulled all the fuses and there was still a draw on the battery. Is the motor warm when it wont start? Have the starter checked as well. I am currently trying to diagnose a starting problem as well and have changed the battery, alt, starter cables and all starter wires and am still having troubles when the motor is warm (no headers-stock exhaust).
  6. Mebes

    Mebes Senior Member
    Messages: 451

    You need to disconnect the neg wire from the battery and then you hook a test light between the wire you just disconnected and the battery terminal that you just disconnected the wire from.
    If you have any electrical load it will light up the test light.
    If you have a large load you will get a bright light and if you have a small load you will have a dim light.
    Start pulling fuses until the light goes out and then you have narrowed down the drain to that fuse.

    2 things to keep in mind.

    A drain like this may come from a fusible link (something that has no fuse to pull).

    And when you are testing if you have the hood up or the door open you may be causing the test light to turn on if you have a hood light or dome light.
    So pull those bulbs or tape down those switches.
    Good luck.
  7. illday

    illday Junior Member
    from RI
    Messages: 9

    yep, the engine is warm when this is happening.
    The battery has juice when this happens, (not enough to
    turn the truck over apparently so I've been using a jump box to jump it when it decharges.

    I'm going to print this thread and try these suggestions this weekend.
  8. JMR

    JMR Senior Member
    Messages: 567

    JMO I would suspect that the problem is with the starter. It probably has a bad brush or worn armature. The battery isn't actually dead. It happens 1 out of 5 times. The extra amperage from the jump box overcomes the poor internal contact in the starter. Traditional testing of the starter will only find it at fault if tested when the problem is occurring. When this happens if the battery were dead, how would it recharge so quickly?. Next time it happens, in a SAFE manner have a buddy TAP the starter with a hammer, while you hold the key to the start position. If it starts, replace the starter.
    Last edited: Mar 10, 2004
  9. TLS

    TLS PlowSite.com Addict
    Messages: 1,425

    You have headers on it....right?

    Its likely HEAT SOAK. The starter needs to be replaced, and while your at it, buy a heat shield for it if you are using headers.

    Also check your ignition timing. Maybe too far ********.
  10. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377


    I think I'll only believe its header heat soak if:

    a) He agrees it has headers :D

    b) They just went on recently

    Its been my experience (nightmare actually, don't ask) that the heat soak problem occurs EVERY time after the engine has run for 5-10 mins or more with headers (on my Beaumont) not just occasionally. I tried numerous starters on that one! And opening it up usually showed normal wear only. My solution was to just buy a hi-torque mini starter that gave more clearance to the exhaust. Worked like a charm.

    But again, like I said, unless its recently installed headers I don't think thats the issue.

    If its not an electrical draw, my second choice would be bad brush in the starter.

    Just a quick question for you guys though, how many of you ARE running headers on a plow truck? They're so thin I'd be afraid of them rotting out in the salt and heat. So far I haven't tried it (I just run the stock manifolds) but was considering it to try and boost torque and efficiency a bit.... not to mention loose a few plounds of the portly front end on the truck!!! ;)
  11. TLS

    TLS PlowSite.com Addict
    Messages: 1,425


    This is the brand I have had on my '90 for the past 11years.


    These are the type you would need for your truck (assuming its a small block).


    They are 14 gauge industrial chrome plated. Only thing rusty on mine are the collector bolts and anything NOT chromed.

    They're about $400, but well worth it. The Tri-Y design really boosts low to mid torque.
  12. Robhollar

    Robhollar Senior Member
    Messages: 766

    My guess it would be a hot start condition. Next time it happens take some water and dump on the starter and see if it starts after cooling down the starter. If that does it then your solenoid is prob going bad. I would consider relocating it on the fender where the heat will be less of a factor. Try the water first, had a dump WITHOUT headers i was always working on the starter.....Rob
  13. jbrow1

    jbrow1 Member
    Messages: 76

    I've got same prob on my 86. Starter I'm sure, so gettin a new one tomorrow. No biggie. If ya decide to put it to rest, I love old chevy's!! : )