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'86 GT 2.8 V6 Charging System

Discussion in 'Electronic Basics' started by Rich Grise, Oct 14, 2006.

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  1. Rich Grise

    Rich Grise Guest

    [crossposted:
    alt.autos.fiero,sci.electronics.basics,sci.electronics.design
    please manage followups intelligently. Thanks! Rich]

    On my '86 GT, with the 2.8L V6 and automatic:

    My alternator belt had been slipping - It would squeal first thing
    in the morning, and I'd notice on the voltmeter on the dash that it
    wasn't reaching full charging voltage. But, it would stop squealing
    before a block, and the volts would come up fine.

    Then one day, it stopped squeling, so I thought, "Kewl."

    But then I noticed that the volts weren't coming up to normal.

    So I went and had the belt tightened.

    Now, the volts seem a little erratic - sometimes it comes up to the
    whole 13.5 (or so - normal car float voltage), but mostly it hovers
    around 11-12V.

    Is it possible for a charging system to be "marginal", i.e., maybe
    if the alternator lost a diode, it might not put out enough charging
    current/voltage? I'm ostensibly an electronics tech, so I should know
    about this stuff, but I'm a little reluctant to go try to troubleshoot
    my car with a VOM. It is the tech in me that suspects a marginal
    alternator, or maybe even the regulator, but I've never seen one of them
    go partly bad.

    The battery would be my last choice, because it's a DieHard that was
    brand new about 2 years ago, and I've been keeping it watered and,
    up until this latest little glitchy thing, well-fed. :)

    Should I just find a shop and ask them to diagnose it, or might there
    be something that a klutz like me could fix with a VOM and a screwdriver?
    (and maybe a few metric wrenches?)

    Thanks,
    Rich
     
  2. Don Young

    Don Young Guest

    Failure of one or more diodes can cause the maximum charging current to be
    low. This can cause a low battery condition when lights or air conditioning
    are being used but adequate charging when loads are low and trips are long
    enough for the battery to become fully charged.

    Since I do not know your skill level or the mechanics of your alternator I
    would suggest having it tested. In our area most of the auto parts stores
    will test it for free.

    Don Young
     
  3. Guest

    A number things come to mind in order of most likely occurance.

    1- worn sticky brushes
    2- blown triode
    3- dirty connections (this could be #1)
    4- regulator (maybe)
     
  4. Also the voltmeter in the dash would not be as good as your DVM but the
    fluctuations dont sound good. Why not put your DVM across the battery
    terminals with the engine running and see what you get. Perhaps set at 200v
    scale to cut back the 'hunting'. As mentioned you should be able to get a
    free test of the battery but be aware of the reason they do them and the
    advice offered :)
     
  5. kell

    kell Guest

    The voltage regulation on just about any modern car is set about 14.5
    volts -- or more -- not 13.5. No.
    With a healthy charging system and battery, your voltage should come up
    to 14.5 pretty soon after starting the car (as measured with a decent
    digital meter, not the dash gage).

    Some reasons the voltage might be low:

    Battery going bad (probably not the case here).

    Battery that has been deeply discharged. A battery that's low enough
    can suck up all the alternator power, holding voltage down. But
    eventually, as the battery charges, the voltage will come up.

    Bad voltage regulator. But they are either good or fail altogether. A
    voltage regulator causing mere inaccuracy or weak charging is unusual.
    I wouldn't think first of a bad voltage regulator based your
    description of the symptoms.

    A bad diode in the three phase six-diode pack. Note that in floating
    field alternators such as the Delcos used on GM vehicles, there is
    another set of diodes besides the heavy rectifiers: the exciter
    diodes. The exciter diodes are much smaller than the output power
    recitifiers because the exciters only have to carry the field current.
    But if you open the alternator to check the heavy rectifiers you should
    also check the exciter diode pack. It has three diodes in it. I don't
    know if they still look like this, but on the older alts I've worked on
    the exciter diode pack is a little orange rectangular plastic thing
    with three tabs on one side and a single tab opposite it. The three
    tabs are connected to the wires on the stator.

    Corroded connections, either in the wiring harness or inside the
    alternator. When I bought my used 86 Burb, it would hardly charge at
    all. Opening up the alternator, I found heavy rust and cobwebs.
    Unscrewed the connections and scraped everything clean, now it charges
    like a champ. Apparently it sat for years in heavy humidity. You
    should also check the wiring harness connections that carry any
    substantial current. Like the battery connections and ground strap,
    for example.

    Pulley on the alternator too big. This results in an alternator that
    turns too slow at idle to charge. I had that problem on an old car I
    owned once.

    There's more, but I'd need to know more about your particular car to go
    much further.
     
  6. Jamie

    Jamie Guest

    talking about that.
    we had a New electronic shift transmission replaced in our (92) dodge
    once. the transmission had sticky torque converter in it but also
    exhibit some problems with shifting..
    after the replacement, the care seem to be better but after about
    5k miles, the shifting problem came back and just got worse..
    it was a $1800 repair job and except for the torque convert not sticking
    any more the shifting problem was still there. so we visited a dealer!
    their answer was, "You need a new transmission, there were problems
    with them", our answer" we just got one ! see our warranty!",
    we ended up parking the car eventually due to it's severity to not
    always shifting into 4th for highway use.
    -- then i donated the car to a friend for around town use ---
    the alternator let go on them after about 6 months., they replaced it.
    guess what! the car shifts perfectly now and she is happy as hell
    knowing that she now has a car with a new Tranny that can go anywhere
    costing her nothing.
     
  7. Rich Grise

    Rich Grise Guest

    .
    Thanks to everyone for the answers - I believe my next step is to take it
    to the shop. I used to work on my own car, when I was 20 years old and
    you could climb into the engine compartment, but I fear those days are
    long past. ;-)

    Thanks!
    Rich
     
  8. Rich,

    It really sounds like it is time to install a rebuilt or new alternator
    which on a Fiero is no walk in the park. I wouldn't want to do it on
    mine and it is only the 4-cylinder model so there is a bit more room.
     
  9. labtech1

    labtech1 Guest

    I replaced my '88 V6 standard with a 160 amp unit, trust me I'd rather do
    the V6 than the 4 cyl engine.
     
  10. Mark Davison

    Mark Davison Guest

    I replaced the alternaor in my 86 GT Auto...and the easiest was was to take
    the rear inner fender assembly out and do it through that opening. At any
    rate, it isn't something I want to do again. Come to think of it, I didn't
    want to do it then either.
    Good luck with your car,
    Mark
     
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