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jlong49686
New User
Apr 9, 2008, 12:41 PM
Post #1 of 4
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i have a 2000 ram van 1500 w/ a 318. i bought it 6 months ago and the guy told me it had a new alternator. i drove it for about 2 months and it went bad again. i assumed it was because it was a used alternator. i replaced it with another used alternator off of a low mileage van about a month ago. its bad again!!! i dont think the alternator is going bad. i believe it is the voltage regulator inside. could something else be wrong that would keep causing this problem??? when i'm driving the volt meter is around 14 volts, if i turn on to many things at once, like the headlights, radio, and heater. the volts drop to 8 and the check gages light comes on. if i shut everything off and then turn off the van and restart it, everything goes back to normal.
(This post was edited by jlong49686 on Apr 9, 2008, 2:44 PM)
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dave284
Enthusiast
Apr 9, 2008, 6:00 PM
Post #2 of 4
(1576 views)
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Re: bad alternator
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I ran into a similar problem ....found out the computer was at fault,cause it controls the alternator's regulator output.
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jlong49686
New User
Apr 12, 2008, 6:12 PM
Post #3 of 4
(1559 views)
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Re: bad alternator
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could it be a bad ground wire or a short somewhere else???
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DanD
Veteran
/ Moderator
Apr 13, 2008, 4:42 AM
Post #4 of 4
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Re: bad alternator
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You can easily test connections & cables with a digital voltmeter and performing voltage drop tests of the positive and negative alternator’s main circuits to the battery.
To test the positive side of the circuit; connect a voltmeter’s positive lead to the alternator’s battery terminal stud. Then connect the meters negative lead to the battery’s positive terminal.
Start the engine and allow it to come up to operating temperature. Turn on all accessories (heater fan, headlights, wipers whatever) and then bring the rpm up to approximately 2000 rpm.
The voltmeter reading should not exceed 0.6 volt; if voltage is above this 0.6, you have a bad connection or high resistance in the cable in between the alternator and battery.
To narrow down where this bad connection or section of cable is; move the negative meter lead down the circuit (cable) away from the battery.
Where you find that the voltage is below the 0.6 volt, you’ve found the problem; it's between the last two test points. Which may mean replacing the cable or cleaning & tightening connections?
If you use a pointed end meter probe, you’ll be able to pierce the cable along its length, to get your readings. Use a dab of silicone to cover & insulate the pin holes you’ve just made.
For the negative side of the circuit; you do it kind of the same way. This time connect the voltmeters negative lead to the alternator’s ground cable stud or alternator case; the positive lead to the battery’s negative terminal.
Run the engine & accessories the same as before; the voltage should not exceed 0.3 of a volt.
If the voltage is above this you would check/repair it the same as you would the positive side.
The reason for switching the positive & negative meter’s leads is to keep the polarity of the meter correct and give you the proper – or + reading on the meter. A digital meter will give you a reading regardless of how it’s connected; you’ll have to keep it strait in your head what you’re reading; -/+.
To see what I mean connect the meter to the battery with the positive lead on the negative battery terminal and the negative lead to the positive battery terminal; the meter will read -12 volts. You won’t hurt the meter or you shouldn’t. LOL
0.3 and 0.6 is a pretty forgiving spec; I would normally only want to see 0.2 or 0.25 of a volt but that’s what the manual said to use?
Dan.
Canadian "EH"
(This post was edited by DanD on Apr 13, 2008, 4:48 AM)
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