Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Alternator shot?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fireinthehole, Aug 19, 2003.

    My 89 Sub's ampmeter/voltmeter (which ever it is) is sitting between 8 and 13. Just started yesterday when I cranked it for the first time. Before that the needle sat right at 13. It still starts and the battery still seems ok, it seems like its still being charged. You think maybe the gauge? I can pull the alternator and have it checked, just dont have time. The Army keeps me busy.

    Thanks- Mat
     
  1. Sample

    Sample 1/2 ton status

    Joined:
    Oct 15, 2002
    Posts:
    536
    Likes Received:
    0
    Location:
    Apache Junction, AZ
    Use a real volt meter at the battery, with the sub running, you should see at least 13 volts.
     
  2. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

    Joined:
    Aug 28, 2002
    Posts:
    9,097
    Likes Received:
    144
    Location:
    california
    Mine does the same thing, Does the guage get closer to the 8 when you have more power using things on? I thought my altenator was going but checked it with a charging and battery tester and was putting out 13.8 with everything on.

    85K5 3/4ton,14b0ltFF,10bolt,9"lift,35"boggers,16.5x14welds, big horse 406SBC/700R4 /forums/images/graemlins/k5.gif /forums/images/graemlins/angryfire.gif
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,980
    Likes Received:
    189
    Location:
    Roy WA
    I second checking it with a "real" voltmeter.

    Measure it with no accessories running, then turn everything you can think of on (lights on high, radio, heater/ac on high) and check it again. As long as it's over 12, you are actually ok, but anything under about 13V and you'll notice the decreased brightness of the headlights and dashlights.

    You can buy rebuild kits for the "earlier" alternators for about $20, and it's a simple task, so if yours is actually putting out very low volts underl load, should be simple/cheap for you to fix yourself.

    Not sure if your alternator will be more costly/difficult to rebuild (not sure what it is) but someone here may be able to comment.
     
  4. Yep, it sits almost to the first line of the orange area. Its strange as it was normal up until yesterday.
     
  5. I checked the voltage at the alternator and it was 11.80, not good is it? I checked it with a multimeter, red probe to the battery cable,black to chassis ground.

    Looks like I need a new alternator.
     
  6. 84_Chevy_K10

    84_Chevy_K10 Banned

    Joined:
    May 30, 2001
    Posts:
    17,669
    Likes Received:
    0
    Location:
    IL, USA
    [ QUOTE ]
    As long as it's over 12, you are actually ok, but anything under about 13V and you'll notice the decreased brightness of the headlights and dashlights.

    [/ QUOTE ]

    Not true. An alternator can't charge a battery at 12v. A car battery is at 12.6+ at full state of charge. If your alternator is only offering 12 volts, your battery is slowly discharging your battery.

    I would put the threshold somewhere around 12.7-12.8 v under load. It really should be closer to 13.6+.
     
  7. the professor

    the professor 1/2 ton status

    Joined:
    Feb 6, 2003
    Posts:
    130
    Likes Received:
    0
    Alot of pretty close answers there
    --
    According to the book..
    --
    12v batteries take 13.2v to charge... or 1.2v OVER the measured voltage of the battery... The last one is trickey, I don't think I ever saw a 'dead" 12v battery, with 8-9v on the terminals charge with 11.5 volts, but who am I to argue...
    --
    In any case, if the open circuit voltage of the battery is say 11.5v, it should charge at 13v etc...
    --
    That said, if a GM alternator is putting out less than 13v at anything over 1500rpm it is probably losing the diode stack... or maby the internal regulator...
    --
    The Alternator on a 1989 is a "single-wire- and requires no connecton to the ignition switch to charge, only a connection to the battery... the wire to the gage and the to the ignition switch is for the guage/light only
    --
    That said, if the alternator was ever changed out to an earlier unit, it will need the 12v "energizer" circuit, through the guage/light to work....
    --
    Confused, sorry...
    /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
     
  8. BlueKnight

    BlueKnight 1/2 ton status

    Joined:
    Mar 6, 2000
    Posts:
    1,518
    Likes Received:
    0
    Location:
    Oregon
    AT idle you alternator should be putting out 12.8ish at above idle 13.8 is a great target voltage. Keep in mind as you add load to your battery your alternator needs to keep up. If your alternator is suspected in failing goto a schucks, kregan, or checkers adn they will test it for me free in car with an incharge 520 tester or the bench. then you will know for sure. The micronics tester is very accurate and can test all aspects of your alt including the field and diode and regulator if its built in
     
  9. Blazn88

    Blazn88 Registered Member

    Joined:
    Dec 11, 2002
    Posts:
    83
    Likes Received:
    0
    Location:
    Northern California
    Fireinthehole--FLW, MO--You wouldn't happen to be in Fort Lost in the Woods Misery would you... /forums/images/graemlins/k5.gif
     
  10. [ QUOTE ]
    Fireinthehole--FLO, MO--You wouldn't happen to be in Fort Lost in the Woods Misery would you... /forums/images/graemlins/k5.gif

    [/ QUOTE ]

    Of course- The greatest place on earth! /forums/images/graemlins/grin.gif I have been here going on 4 years.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,980
    Likes Received:
    189
    Location:
    Roy WA
    [ QUOTE ]
    ot true. An alternator can't charge a battery at 12v.

    [/ QUOTE ]

    That's why I said "over 12". /forums/images/graemlins/smile.gif

    You can run your vehicle at 10 volts if you like, but if an alternator is putting out over 12 volts under a full load, you aren't drawing the battery down past where it needs to be. Alternator increases output based on demand when working correctly, (and thus, your battery will never decrease in voltage) if that doesn't happen, it needs rebuilt.

    As I also stated, it's still not optimum, just that it will work.
     
  12. bryguy00b

    bryguy00b 3/4 ton status

    Joined:
    Apr 7, 2002
    Posts:
    5,587
    Likes Received:
    0
    Location:
    Rochester, N.Y
    mine just went on me...i was just lucky to have another one sittin on the oll shelf of junk in my garage. /forums/images/graemlins/thumb.gif
     
  13. I replaced my alternator today with a new one. The old one was dying fast. My Sub was getting harder to start each time. I had the old one checked as well and it was putting out only 11.5, new one is putting out 13.5-13.6.

    Thanks for all the replies.

    Mat
     
  14. Blazn88

    Blazn88 Registered Member

    Joined:
    Dec 11, 2002
    Posts:
    83
    Likes Received:
    0
    Location:
    Northern California
    I did my basic there. Had some great times and alot of fun.. /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/k5.gif
     

Share This Page