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Voltage Drop at WOT?

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Old 04-12-2012, 08:06 AM   #1
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Default Voltage Drop at WOT?

So my check gauges light comes on because my voltage drops to 9 when I floor this thing all of a sudden. Delco alternator installed about 4 months ago. 2001 Camaro drivetrain installed in my rx7 complete with Fbody gauge cluster. Haven't had a chance to hook a volt meter up and drive it yet, just wondering if this is a some what common problem?
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Old 04-12-2012, 09:36 AM   #2
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Start the car then take the positive terminal off and see if it dies. if it does than replace the alt'.
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Old 04-12-2012, 11:59 AM   #3
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You check belt and tensioner? Almost sounds like belt slip possibly.
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Old 04-12-2012, 12:08 PM   #4
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Had the same problam i changed tensioner and belt no change. Got alternator checked several times they said it was fine my battery was weak changed battery no change. Finally bought a high output aftermarket alternator and that fixed the problem.
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Old 04-13-2012, 11:22 AM   #5
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Quote:
Originally Posted by LS14EVR View Post
You check belt and tensioner? Almost sounds like belt slip possibly.
+1. If you old alt was fine for the car, the new one should be properly sized, also.

You could also have a pulley issue on the new alternator? You may want to check the grooves and the spacing of the pulley from the body of the alternator.
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Old 04-15-2012, 03:44 PM   #6
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Finally got around to testing it, and hooked a voltmeter to my cig lighter, first thing I noticed was my gauge cluster was reading just a hair below 13v and the voltmeter was at 13.74v. So went for a drive and under WOT once I reach about 4500rmps the voltage starts to drop, stock gauge gets vague, but voltmeter showed a lowest of 11.6v. It was pretty consistent too. Kinda hard to hear anything over the exhaust so not too sure if belt is slipping or not. May replace tensioner and belt to be safe and see what happens. Any suggestions if that doesn't cure it?
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Old 04-15-2012, 04:02 PM   #7
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truck alt FTW !!!!
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Old 04-17-2012, 11:02 AM   #8
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The best I can come up with is belt slippage, so I ordered a crane cams manual belt tensioner, and new belt. I should know later this week if it cures it.
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Old 04-17-2012, 11:07 AM   #9
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The best I can come up with is belt slippage, so I ordered a crane cams manual belt tensioner, and new belt. I should know later this week if it cures it.
Did you confirm that your alternator pulley is correct and that the marks on the stock tensioner are within range? (Those marks should tell you if your tensioner is bad or if there is a belt issue.)
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Old 04-17-2012, 11:38 AM   #10
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I have also had one alternator test out fine on a bench tester, but when I took it to a alt. rebuild shop, he wanted to test it while still on the car and he did. That was the only way it showed it was bad, and it wasn't totally bad, it was hit or miss. Even when he put it on his bench it showed it was partially good. He said in his 30+ years of rebuilding he had never really seen anythign like it. Replaced it and it was fine.
SO there are the unexeplainable ones out there.
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Old 04-19-2012, 10:57 AM   #11
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Tensioner did not fix the problem. Back to square one. FML.
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Old 04-20-2012, 01:22 AM   #12
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psssst.............truck alt
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Old 04-20-2012, 01:23 AM   #13
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http://ls1tech.com/forums/generation...-failures.html
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Old 04-20-2012, 08:45 PM   #14
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I found a few local for about $45. I'll give it a shot.
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Old 04-22-2012, 01:45 AM   #15
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also the pcm turns the alternator off at wide open throttle for performance aspects
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Old 04-22-2012, 02:09 AM   #16
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Quote:
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also the pcm turns the alternator off at wide open throttle for performance aspects
my voltmeter does not read ZERO when i go FT......seems a car would need the volts at FT ........not less volts.........the batt can only supply so much
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Old 04-22-2012, 10:20 AM   #17
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I have seen the same problem in my Delco rebuild.
It seems as if the alternator turns itself off around 6000 RPM; when the RPMs get below that point, it turns back on again.
The original alternator did not do this.

I assumed that the internal voltage regulator regulator installed durring the reman process was doing this in order to preserve the life of the unit, and reduce warranty claims.
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Old 04-22-2012, 12:11 PM   #18
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Quote:
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also the pcm turns the alternator off at wide open throttle for performance aspects
I'm about 100% sure this does not happen, unless I missed something in engineering school. The only way you are going to "turn it off" is to stop it spinning, so unless you're car has a accessory belt that the pcm can shut off at any time, there would be no performance gained. You are still spinning the alternator. MAYBE the regulator could cut the voltage at high rpm but there is no need. Nothing is gained.
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Old 04-22-2012, 09:52 PM   #19
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it does it turns of the exciter circuit in the alternator trust me my brother works for delphi as an electrical engineer the pcm also doesnt allow the ac compressor to come on the pcm will temporarily disable the alternator output for that the battery should be able to supply the ignition system, the ignition system only needs 12v going in and the coil basically a small powerful transformer produces the high voltage, when the pcm sees the voltage drop below a certain threshold it will excite the generator and all ow it to produce voltage, the voltmeter should never read zero unless the battery is a boat anchor
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Old 04-22-2012, 10:00 PM   #20
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also anytime you spin a alternator faster it produces a stronger magnetic field which in turn loads the alternator causing drag, the reason the pcm does this is due to acc drag on the engine i will find the actual delphi engineering study from my brother and they found this to be woth a total of 7 hp at wot also newer cars dont do this cause newer alternators are pwm and the ezcite circuit is actually turned off and on in a percentage
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