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Diagnosis Skills

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by rich'90, Oct 16, 2000.

  1. rich'90

    rich'90 1/2 ton status

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    Would not want you guys to get rusty diagnosing problems, so here is one for you.
    This just started happening today. Normally the voltmeter will read around 13. When accelerating hard it will drop drastically, everything will dim and the engine almost cuts out. During normal driving it is fine. The alternator is less than 1 year old.
    Any suggestions?
    Thanks

    Go heavy or Go home[​IMG]
     
  2. rich'90

    rich'90 1/2 ton status

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    Forgot to ask, is there a voltage regulator that will cut the power out if the alternator is putting out too much and is it possible to over-rev the alt?
    Thanks again

    Go heavy or Go home[​IMG]
     
  3. coopertwpk

    coopertwpk 1/2 ton status

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    Sounds like your belt is going,or your battery cable is torched mine was the cable by the starter .pepboys sells the 2#cables behind the counter better than stock and fit perfect also they have the dual battery cables identicle t stock.
     
  4. 6.2 man

    6.2 man 1/2 ton status Premium Member

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    I would also guess loose belt ????
     
  5. rich'90

    rich'90 1/2 ton status

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    I thought loose belt at first too. Checked the tension and condition and all are fine. The belt was replaced when the alternator was. Any other ideas? It is still drivably as long as I don't gun it(which I rarely do) but i would like to figure it out and fix it.
    Thanks

    Go heavy or Go home[​IMG]
     
  6. Blue85

    Blue85 Troll Premium Member

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    I would check all of the wiring to the alternator, including the small wires that control the alt, as well as all of the ground straps between the battery, engine block and chassis.

    Do you lose voltage at high rpm, or anytime the engine is under heavy load?

    You can't rev the alternator too high unless you have a) put a different size pulley on it or b) modified your engine to run at 6000 rpm or more. I think it is important to determine whether the voltage regulator is internal to the alternator or done by the ECM in a '90. Anyone know?

    The fact that you are losing all power means that even the battery is not well connected to the engine under certain conditions. Since you can still start the truck, the battery is either not to blame or not fully to blame. It's possible that the alternator is bad and is shorting internally at high rpms. This, coupled with a poor battery connection, could produce the symptoms that you are describing. Why not try running around the block with the alternator disconnected to test this theory?

    '85 JIMMY
    '90 paint/grill/trim 5"susp 33/12.5/16.5
    Fresh 350 B&M '87 TH700
     
  7. sosamantx

    sosamantx 1/2 ton status

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    <font color=blue>It sounds like the alternator or voltage regulator to me. How do your battery connections look, is there enough fluid in the battery? If you are able to take the caps off, the fluid level should be just above the metal plates that are down there, DON'T OVERFILL, people tend to fill them up with water and when you put on the caps, fluid goes everywhere. Are your cables tight, meaning you can't twist them off with your hand on the battery, and what about the other ends, where it is grounded to the block, and/or starter, what about corrosion on the terminal ends? Ideally, just run it up to your local autoparts and have them check out the battery and alternator. - Steve</font color=blue>

    <font color=blue>Steve Sosa a.k.a. "sosaman"</font color=blue>
    http://sosaman.home.texas.net/carpics.html
     
  8. rich'90

    rich'90 1/2 ton status

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    Thanks, I will try all of the above and let you all know.

    Rich

    Go heavy or Go home[​IMG]
     
  9. rich'90

    rich'90 1/2 ton status

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    Just to keep you guys up to date, it was basically just what you all said. A loose belt. Not in the usual way though. When the engine was not running the belt tension was fine but when under heavy loads it was loose for some reason. Puzzled me until I took off the alternator. Broken accessory mount. When I gunned it the whole unit rotated. Unfortunately the mount is al. so no JB weld. Still looking for one in the junkyard.
    Have a good weekend.

    Go heavy or Go home[​IMG]
     
  10. stephan van leir

    stephan van leir 1/2 ton status

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    It`s you`r regulator. Look foor a shop in you`r area that will do the rebuild. What ever you do don`t buy a cheap Pep boys type alt. Often the cheap units are only rebuilt enough to get them running again. So what you get is paint and new brushes for you`r hard earned cash!
     
  11. sosamantx

    sosamantx 1/2 ton status

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    <font color=blue>So the alternator mount (bracket) was flexing? Or you said (accessories) was flexing? Just trying to picture it. - Steve[/url]

    <font color=blue>Steve Sosa a.k.a. "sosaman"</font color=blue>
    http://sosaman.home.texas.net/carpics.html
     

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