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Disappointing weekend ... alternator

Discussion in 'Technical Q&A' started by olehholy, Mar 20, 2006.

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  1. olehholy

    olehholy Karting

    Nov 12, 2003
    122
    NJ
    Full Name:
    Oleh Holynskyj
    #1 olehholy, Mar 20, 2006
    Hello All:

    I have been chasing a charging systen progemlm in my 84 QV for some months now. I get barely 12.25 volts at the battery at idle with little or no change with RPM. When I fully charge the battery, it will run for about 1 week or so and then go dead. Not surprising given the inadequate voltage while running.

    Over the last few months leading up to this weekend I have done the following

    - had the battery test twice - good both times
    - installed Birdman's fuse panel
    - did a cursosry inspection of cables, including the cluster of cables at the starter, looked good and tight, so did neg ground strap.

    I concluded, it is most likely the alternator. So, a rare oppurtunity to work on the car arose this weekend. I purchased a rebuit unit from T.Rutlands and went to work. Once again, Verells write-up on alternatoer removal on this board was extremely helpful and spot-on ...... thanks Verell.

    Unforutnalty, upon restart, I still only get the 12.25 at the battery at idle with little or no movement with RPM.

    Tonight, I am going to measure voltage at the cluster of cables at the starter, which I should have done in the first place. If I get good voltage at that location, how many stops along the way to the battery does the cable make where it could have a fault in it ? Any other connections I should check ?

    Many thyx,

    Oleh
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,932
    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #2 Steve Magnusson, Mar 20, 2006
    Last edited by a moderator: Sep 7, 2017
    The schematic for your '84 308QV is shown in your OM.

    You're on the right track to check things between the starter and the alternator next -- two things you might check:

    1. Measure the voltage on the Cu10R (large red) wire going from the starter, item 10, into the alternator, item 6 (relative to the stud on the chassis holding the engine ground strap) -- should be about +12.6V when the engine is not running and 14~14.5 V when the engine is running.

    2. Also try measuring the voltage between the alternator metal housing and the stud on the chassis holding the engine ground strap with the engine running -- should be ~0V. If you get ~+12V you have a grounding problem somewhere between the alt. housing and the chassis.

    Good hunting...
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  3. olehholy

    olehholy Karting

    Nov 12, 2003
    122
    NJ
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    Oleh Holynskyj
    #3 olehholy, Mar 20, 2006
    Thanks Steve,

    Will do those checks tonight as you suggest. I looked at the wiring diagram last night and it looks like the positive battery cable is a home run from the starter to the battery terminal. I read on another thread that the mondials of the same vintage do have an interim connection somewhere before the battery that is prone to deteriorate. I wonder if that is the case on these QV's.

    Thanks agin,

    O
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,932
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #4 Steve Magnusson, Mar 20, 2006
    Since your starter motor is working OK, I don't think that you need to worry about the connection from the "+" battery terminal to the starter terminal (and I believe 308 do not have any other connections in that path -- but not 100% sure about that).
     
  5. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,022
    Groton, MA
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    Verell Boaen
    #5 Verell, Mar 20, 2006
    When you start the car, the alternator light should come on & stay on until the engine is rev'd up to 1,500 to 1,800 RPM, then go out & stay out.

    If the light doesn't come on, that could be your problem. The bulb & it's wiring provide initlal power to excite the alternator's field coil until the alternator is generating enough voltage to excite the coil it'self (that's when the light goes out).

    A bad bulb, or bad connection anywhere in that circuit will result in the alternator not coming on-line.

    Yes, if the starter cranks over fine with a charged battery, then the starter-battery cable, and also the battery to frame, & engine to frame ground circuits are OK & can be eliminated.

    There's one other odd-ball 308 alternator problem to look for: The alternator pivot bolt is mounted on rubber bushings, so sometimes the pivot bolt doesn't provide a ground path for the alternator case. The case then gets grounded to the timing belt cover thru the tension adjustment bolts & bracket which can get corroded & provide a poor connection even tho they look OK.

    Fix is to ground the alternator case directly to the engine. I can't remember the specifics of this, it could have been either some way of making sure the ground goes thru the pivot bolt & bracket, or it may have been just running a heavy ground cable from the alternator's adjustment bolt to the engine. Somewhere in the archives is a thread.
     
  6. olehholy

    olehholy Karting

    Nov 12, 2003
    122
    NJ
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    Oleh Holynskyj
    #6 olehholy, Mar 20, 2006
    Hi Verell:

    Thanks for the input. My alternator light is working as you stated. It comes on breifly upon initial startup and then goes out at the first blip of the throttle. It did so with the old alternator also, which is why I was holding out on swapping it, hoping it was something else. Also, even with the old alternator, when I would disconnect the battery, the car continued to run fine.

    Anyway, I think tonights test of measuring output right at the starter terminal should tell me what is going on. I will also test it that way running with the battery disconnected to see if maybe it really is a shorted or partially shorted battery pulling the voltage down.

    Thx,

    Oleh
     
  7. olehholy

    olehholy Karting

    Nov 12, 2003
    122
    NJ
    Full Name:
    Oleh Holynskyj
    #7 olehholy, Mar 20, 2006
    Hmmmm ..... I think you guys are onto something with the ground issue. If the alternator ground is suspect via the lower pivot bolt due to the rubber bushing then, as Verell stated, its only path is via the slotted bracket where the adjustment bolt attaches. I noticed when I was installing the new alternator that the slotted bracket swung to and fro quite easily. Perhaps that is indicative of poor ground.

    stay tuned ............
     
  8. olehholy

    olehholy Karting

    Nov 12, 2003
    122
    NJ
    Full Name:
    Oleh Holynskyj
    #8 olehholy, Mar 21, 2006
    You guys were spot on. Looks like it is alternator ground. When I measured voltage between the + side batt terminal and the alternator case, I get a nice 14.5 volts at idle. It seems the pivot bolt is not providing ground due to the bushing and the slotted bracket to which the adjustment side of the alternator bolts to is loose as hell.

    In addition to cleaning up and tightening the slotted bracket, maybe I should run a heavy guage cable from the adjustment bolt to the engine block, perhaps to one of the 3 nuts/studs holding the pivot bolt bracket to the engine block.

    Many thanks to you guys,

    Oleh
     
  9. olehholy

    olehholy Karting

    Nov 12, 2003
    122
    NJ
    Full Name:
    Oleh Holynskyj
    #9 olehholy, Apr 7, 2006
    Just wanted to post an update on the poor ground situation. I located the engine to chassis ground strap. It was hard to find becasue I was looking for a braided silver strap, but it was so coated with grease and oil that it resembled a black leather belt. Anyway I took it off, cleaned the cable up and then used a drill-mount wire brush to clean all of the contact surfaces, on the cable and the chassis points.

    The result, was 13.8 V at the battery. It pays to inspect that strap evey now and then.

    Oleh
     

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