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1995 Pontiac Bonneville Question: Why does my voltmeter dive or fluctuate, and engine hesitate

 

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doug henry, 3.8L V6, Dallas, TX, November 06, 2013, 18:47
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my voltmeter dives or stays in red, and engine hesitates or stalls.i have rplaced alternator and battery but problem got worse.

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  • Answer #1

    pushrod November 06, 2013, 19:08
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     Master

    Good place to start on this is the battery cables! Most overlooked part of any vehicle and problems with these vehicles, even if it cranks ok!! There are two cables hooked up to the positive post, take both off, remove all componets, clean everything that you find there, look close at everything!! Then clean them again and install. Do the negative while your at it. Not saying this is the fix, they just give a lot of problems and may be yours.

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  • Answer #2

    cardocIII from Gillespie's Auto Service, November 06, 2013, 20:13
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     Master

    Do you have a voltmeter? Measure the system voltage at the battery key off engine off, write that first measurement down. 12.3v or less and you need to put a charger on the battery and bring it up. 12.4 and higher, the battery will fully recover once the charging system is working correctly. Start the engine and re-measure the voltage at the battery. If its still the same as before you started the engine or less, then the alternator isn't charging, or power isn't getting to the battery. At the alternator there is the heavy wire on the output terminal, measure from that point to battery negative and see if it matches what you had at the battery. If it is higher then just as #1 stated you likely have a corroded connection at the battery cables. If it is the same then go to the other two wires in the small connector. One of them is red, and you should see battery power on that wire both when it is plugged in and when it is disconnected. The smaller brown wire should be battery voltage when the engine is running and no voltage when the engine is off. The reason is power should be flowing through the instrument cluster to excite the alternator when you first turn the key on. In most cars that would be a charge lamp circuit and you would see the light on because it is grounded by the regulator inside the alternator. When the alternator starts charging it puts 12v on that terminal and that puts power on both sides of the lamp and makes it turn off. If you don't see power there, try unplugging it and see if you measure power. If you still don't see power there, connect a test light to the battery positive, start the engine with that two wire connector plugged in, and back probe the brown wire. Your testlight should light momentarily and then you'll notice it go out and the alternator should then be charging. If that works then you have an open in the excite circuit in the instrument cluster. HTH

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  • Answer #3

    Greg's Orange Auto (12205 Answers) , Orange, CA - (714) 361-9386
    globalhelper November 07, 2013, 05:49
     Master

    have charging system ck then battery and cables for corrision

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