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Voltage Drops Under Load

This is a discussion on Voltage Drops Under Load within the General Help forums, part of the LSx Technical Help Section category; Problem just started a few weeks ago. When I step on the gas to leave from a stop light or ...

  1. #1
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    Voltage Drops Under Load

    Problem just started a few weeks ago. When I step on the gas to leave from a stop light or have the steering wheel cranked the voltage drops and the warning light on the dash comes on. As soon as I lift off the gas or shift into a gear above 2nd the voltage goes back to where it should be. I can cruise all day on the highway no problem. When it first happened I tested the battery and it wasn't great so I replaced it. It's not as bad now as before, but still happens so that was a symptom as opposed to the cause.

    I'm thinking maybe the belt is slipping (original belt on a 1998 with 37K miles) which maybe a problem with the tensioner or belt is just stretched out. Of course it could be the alternator as well. Any way to check the tensioner or the belt so eliminate them as culprits? Anything else I should be checking?

    Thanks much

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    Just saw in another post that power steering fluid getting on the alternator may cause it to go bad. That may explain my issue as cap blew off the reservoir the last track day I did and sprayed fluid all over the engine bay and a few weeks later the high pressure hose failed and sprayed PS fluid all over the alternator (among other things).

  3. #3
    Veteran 0rion's Avatar
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    you've pretty much got it nailed down I think.....just a matter of singling out what it is. If the belt was slipping I believe you would hear it squeal. My first thought was an alt. issue but the fact it's doing it at wot and during turns also points pretty strongly at the belt or pulley. Any unusual noises up there from the belt or pulleys?
    Do you have a volt meter? Put it across the battery terminals at idle and see if the alt. voltage is fluctuating much or staying steady. Should read in the 14.4 range and stay pretty steady. I've seen them read 14 for a little bit then drop to 11 for a couple seconds then back to 14 and things like that. If it's fluctuating that's a sure sign the alt. is in the process of failing. Has the battery drained down at all or is it just the light coming on?

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    Thanks for the reply. No noises are coming from the belts. I don't have a voltmeter but I have had enough electrical issues with cars in the last year that I'll pick one up and check. Just looking at the gauge on the dash, it doesn't budge when the car is just idling, but I know that's not the best measure.

    Thanks again

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    Senior Member Too Fast's Avatar
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    Most likely the alt is going. Belts, tensioners on these cars are pretty reliable. You'd hear the belt complain (squeal) when you put the steering wheel at full lock if it was slipping, since this belt runs the alt/ps/wp.

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    don't forget that you can unhook the battery while the car is running to test the alternator.
    If it keeps running with no battery then the alternator may not be the problem

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    Interesting. I didn't think about unhooking the battery. Thanks for the idea.

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    Quote Originally Posted by jimmi7769 View Post
    don't forget that you can unhook the battery while the car is running to test the alternator.
    If it keeps running with no battery then the alternator may not be the problem
    Quote Originally Posted by moltkewhy View Post
    Interesting. I didn't think about unhooking the battery. Thanks for the idea.
    Thats an old school trick that is no longer recommended on modern cars. There is a possibility for alternator damage or other vehicle electronics damage.

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    Smiles for 9.5 Years cammed goat's Avatar
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    Quote Originally Posted by Cutlass View Post
    Thats an old school trick that is no longer recommended on modern cars. There is a possibility for alternator damage or other vehicle electronics damage.
    Voltage spikes FTL.

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    Senior Member Too Fast's Avatar
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    Quote Originally Posted by Cutlass View Post
    Thats an old school trick that is no longer recommended on modern cars. There is a possibility for alternator damage or other vehicle electronics damage.
    Quote Originally Posted by cammed goat View Post
    Voltage spikes FTL.
    +100.

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    yep, these cars aren't like dad's old small block. Way more sensitive electronics on board these engines.

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    Quote Originally Posted by jimmi7769 View Post
    don't forget that you can unhook the battery while the car is running to test the alternator.
    If it keeps running with no battery then the alternator may not be the problem
    Good way to cook your ECM..
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    Thanks for warning me off it. Voltmeter it is.

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    Turned out to be a loose connection on the alternator. I thought I had checked them, but not good enough apparently. My tip off was I hit a pothole and saw the warning light flicker on for a second. I went back unplugged, cleaned and plugged back in all the alternator connections and problem solved.

    Occam's Razor applies again. Looking for complicated solution when all it needed was a simple connection to be made.

    Thanks for all the advice.

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    Veteran 0rion's Avatar
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    glad you got it figured out. Most of the time it ends up being something simple or something you've overlooked. I like those repairs because at the end of the day they're cheap and easy.

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    I love the cheap easy fixes as well!

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