View Full Version : Voltage Drop at WOT?


LS1Pariah
04-12-2012, 08:06 AM
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?

Tramminc
04-12-2012, 09:36 AM
Start the car then take the positive terminal off and see if it dies. if it does than replace the alt'.

LS14EVR
04-12-2012, 11:59 AM
You check belt and tensioner? Almost sounds like belt slip possibly.

01ls1v8
04-12-2012, 12:08 PM
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.

wssix99
04-13-2012, 11:22 AM
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.

LS1Pariah
04-15-2012, 03:44 PM
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?

sjsingle1
04-15-2012, 04:02 PM
truck alt FTW !!!!

LS1Pariah
04-17-2012, 11:02 AM
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.

wssix99
04-17-2012, 11:07 AM
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.)

LS14EVR
04-17-2012, 11:38 AM
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.

LS1Pariah
04-19-2012, 10:57 AM
Tensioner did not fix the problem. Back to square one. FML.

sjsingle1
04-20-2012, 01:22 AM
psssst.............truck alt

sjsingle1
04-20-2012, 01:23 AM
http://ls1tech.com/forums/generation-iii-external-engine/1287967-fix-my-endless-alternator-failures.html

LS1Pariah
04-20-2012, 08:45 PM
I found a few local for about $45. I'll give it a shot.

fastazzls1
04-22-2012, 01:45 AM
also the pcm turns the alternator off at wide open throttle for performance aspects

sjsingle1
04-22-2012, 02:09 AM
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

Fireberg
04-22-2012, 10:20 AM
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.

LS14EVR
04-22-2012, 12:11 PM
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.

fastazzls1
04-22-2012, 09:52 PM
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

fastazzls1
04-22-2012, 10:00 PM
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

fastazzls1
04-22-2012, 10:02 PM
also the a/c is controlled with a clutch, no think of the stator and rotpr as a clutch in the alternator,look it up ford has been doing this for years, and i work for porsche as a tech and they also do the same thing

fastazzls1
04-22-2012, 10:13 PM
it does not turn it a 100% of but greatly limits its output to near nothing anyone who tunes can tell you this sorry for shitty posts i am driving and on my i phone

fastazzls1
04-22-2012, 10:15 PM
At high speeds, the on-time may be 10 percent with the off-time at 90 percent. At low speeds, the on-time may be 90 percent and the off-time 10 percent.

this is directly from GENERAL MOTORS

sjsingle1
04-23-2012, 01:20 AM
need a reference......nothing in my factory manual

LS14EVR
04-23-2012, 11:13 AM
Well, if we can see the reference from Delphi, then I'd like to see it. Interesting. I'd like to learn more. I know you can turn on and off the compressor. It's got a clutch, but never knew they could with the alternator.

wssix99
04-23-2012, 04:29 PM
http://en.wikipedia.org/wiki/Alternator

it does it turns of the exciter circuit in the alternator

Could be. At higher RPMs, some alternators can self-excite. This doesn't mean that the alternator turns itself "off." The engine needs electricity to fire the spark plugs. The faster the engine turns, the more the spark plugs fire. The more the spark plugs fire, the more electricity is required. The alternator can not stop working at the point of the highest electrical demand!

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,

You should check with your brother again on this... I'd bet that its just the exciter.

also anytime you spin a alternator faster it produces a stronger magnetic field

Nope, the alternator turns a winding through a magnetic field. You have generators and motors mixed up here. The process of turning the alternator through the magnetic field takes force to accomplish.

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

Sure, if you can self-excite, you can turn off the exciter and safe some hp. But again, this doesn't mean that the alternator is no longer producing electricity, its just doesn't need the extra help from the exciter circuit.

the voltmeter should never read zero unless the battery is a boat anchor

THIS, THIS, THIS! is a great point. If an alternator is failing, the voltage should drop slowly as the battery drains. The OP's problem could just be a loose wire that is getting knocked around as the engine kicks at high RPM.

LS1Pariah
04-25-2012, 07:56 AM
AND THE WINNER IS!

Ding! Ding! Ding!!

The truck alternator!
Thanks for playing, /topic.

RPM WS6
04-25-2012, 12:58 PM
also the pcm turns the alternator off at wide open throttle for performance aspects

the pcm will temporarily disable the alternator output

I disagree, but you don't have to take my word for it. All you have to do is run a scan log and track voltage before and during WOT. If the system is working properly, you won't see the significant voltage drop that would be associated with the alternator/charging capabilities being "shut off" at WOT as you have stated.

Furthermore, the truck alternators may be a superior design, and obviously have provided some relief for some people having charging issues, but it's not getting at the original root of their problem IMO. These engines/cars were able to charge adequately (albeit a bit low at idle with a full accessory load) with stock electrical systems and stock charging components when new, so unless you've added additional load or are using a poor quality rebuild, then the issue is more than just charging capacity of the alternator - and the higher output truck units are likely just masking other issues. I think more often than not, the real issue is people getting rebuilds that are not of the same quality as the OEM original alternator. I've had lots of disappointing rebuilds from retail parts store chains over the years myself.

wssix99
04-25-2012, 06:50 PM
Furthermore, the truck alternators may be a superior design, and obviously have provided some relief for some people having charging issues, but it's not getting at the original root of their problem IMO. These engines/cars were able to charge adequately (albeit a bit low at idle with a full accessory load) with stock electrical systems and stock charging components when new, so unless you've added additional load or are using a poor quality rebuild, then the issue is more than just charging capacity of the alternator - and the higher output truck units are likely just masking other issues. I think more often than not, the real issue is people getting rebuilds that are not of the same quality as the OEM original alternator. I've had lots of disappointing rebuilds from retail parts store chains over the years myself.

AMEN!!! If the problem came with the installation of a different alternator, something other than the alternator sizing is the issue.

sjsingle1
04-25-2012, 08:03 PM
would not trade my truck alt for a pile of gold.......well maybe ;P

lil-bit
04-27-2012, 10:25 PM
So get a new alt?

sjsingle1
04-28-2012, 04:04 PM
so few places you can get a NEW alt......99% are remans

1ltcap
04-28-2012, 04:05 PM
start the car then take the positive terminal off and see if it dies. If it does than replace the alt'.

DO NOT DO THIS.

this is a good fast way to cook your ecu.

1ltcap
04-28-2012, 04:12 PM
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.

an average alternator costs about 5 hp to run. there is an advantage to turning it off, which can be done. honda's been doing it for years.

RPM WS6
04-28-2012, 04:51 PM
an average alternator costs about 5 hp to run. there is an advantage to turning it off, which can be done. honda's been doing it for years.

I can't speak for every/all applications, but I can say that this is not how the LS1s work. I've run many scan logs of WOT voltage in the past, due to an issue I was diagnosing several years ago, and I can tell you that alternator output does not drop off to nothing or near nothing at WOT with a properly working system (LS1).

Anyone that wishes to test this can do so quite easily and see for themselves if they have a comprehensive OBD scanner.

1ltcap
04-28-2012, 05:48 PM
I can't speak for every/all applications, but I can say that this is not how the LS1s work. I've run many scan logs of WOT voltage in the past, due to an issue I was diagnosing several years ago, and I can tell you that alternator output does not drop off to nothing or near nothing at WOT with a properly working system (LS1).

Anyone that wishes to test this can do so quite easily and see for themselves if they have a comprehensive OBD scanner.

i wasn't saying that these cars can do it...or that they do. i was simply stating that it can be done.

LS14EVR
04-29-2012, 12:18 PM
Well, I guess I learned something new today. That is can be turned off so to speak. I would like to see some real world testing numbers of how much is gained by doing this. 1ltcap says 5hp, but is that by removing it from the belt all together, or just by so called turning it off?

1ltcap
04-29-2012, 01:17 PM
Well, I guess I learned something new today. That is can be turned off so to speak. I would like to see some real world testing numbers of how much is gained by doing this. 1ltcap says 5hp, but is that by removing it from the belt all together, or just by so called turning it off?

no.....simply turning it off. if it's not producing voltage, then it simply freewheels.

DisasterFormula
04-29-2012, 03:43 PM
i wasn't saying that these cars can do it...or that they do. i was simply stating that it can be done.

If you knew that F-bodies don't do it, then why the fck would you come in here talking about it and just trying to confuse everyone. Absolutely no relevance to this topic. That's like someone asking, "What company had the first variable displacement prototype," and you go and tell 'em, "Well Honda started doing their version of it in 2005." :bang:

1ltcap
04-29-2012, 11:27 PM
If you knew that F-bodies don't do it, then why the fck would you come in here talking about it and just trying to confuse everyone. Absolutely no relevance to this topic. That's like someone asking, "What company had the first variable displacement prototype," and you go and tell 'em, "Well Honda started doing their version of it in 2005." :bang:

where in any of my posts does it become obvious that i knew these cars don't do this?

DisasterFormula
04-29-2012, 11:37 PM
where in any of my posts does it become obvious that i knew these cars don't do this?

My bad man, for some reason I thought you were fastazzls1. No sleep for two days is great for confusing oneself. :bomb: