Low voltage until I WOT
10-17-2015, 08:51 AM
#1
Low voltage until I WOT
Hey guys, I have a weird annoying problem. Every time I start my car and go to drive somewhere the car will turn over completely fine but the voltage will stay right above the red zone while it's running. When I put it in drive and start driving down the street it bogs really badly, the lights are dim, and the Windows go up slowly until I can slowly ease it up to WOT. once I open the throttle all the way the volts shoot up to around 13-14 and the car is fine and runs good again.
This used to be a very intermittent problem but now it's every single time I start it up when the car is cold. I used to think the gauge was sticking but the Windows go up insanely slow and the dash lights are dim so I know the cars not putting out enough volts to send a good spark to the motor causing it to bog.
The battery is literally 3 weeks old and the alternator was replaced in February-March. Thanks guys
This used to be a very intermittent problem but now it's every single time I start it up when the car is cold. I used to think the gauge was sticking but the Windows go up insanely slow and the dash lights are dim so I know the cars not putting out enough volts to send a good spark to the motor causing it to bog.
The battery is literally 3 weeks old and the alternator was replaced in February-March. Thanks guys
10-17-2015, 09:27 PM
#3
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Re: Low voltage until I WOT
Sounds like a wonky connector somewhere.
Trace it out with a voltmeter from the alt to the battery.
Trace it out with a voltmeter from the alt to the battery.
10-18-2015, 11:13 AM
#8
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Re: Low voltage until I WOT
I don't recall the exact voltages off hand but I've posted them many times before if you want to try to search.
With the engine off, you're reading the resting battery voltage. That should be around 12v or a little less.
While running IIRC it's around 14.4, but if it goes over 15.5 it's overcharging and can damage or cook your battery. You would also notice that your headlights and interior lights are brighter than normal.
(The alt blindly generates as much as it can while the regulator limits the upper limit. That said, the regulators are often inside of the alternator anyway. But you can disassemble it to replace it if you want.)
Many people make the mistake of simply checking once and letting it go at that. Or, maybe taking it in to get it checked, but it's my opinion that you can more effectively check both the alternator and battery with a meter and sometimes with a home made lead that plugs into a cigarette lighter. The actual voltage may be slightly less doing it this way, but not enough to have any meaningful value.
If the voltages checks out at rest and while running from the engine bay, then you would use the cig lighter lead to check the voltage while starting. If it drops from say 11v to less than 9, the battery does not have enough capacity. The lead that I mentioned can also be used while driving so you can know the exact voltages when those symptoms occur, and you'll also know about where the needle is on the cluster gauge for various voltages. With what you are describing I'm guessing that when it gets clsoe to stalling you'll see something around 13v and often at 12v which will mean that your car is running off of the battery.
Yes you can bring in both the battery and alternator to get them load tested but you already have load testers in the car itself. What this does is it includes your connections (good or bad), and also includes how the various operating temperatures like heat or cold affect your system. Or even if something were to vibrate loose or move affecting your connection.
What I think you have is a failing alternator. You can verify this by watching the voltage with the car running and then turning on and off headlights and other accessories. As the alternator wears out it isn't as efficient and can't produce as much as it used to. Another possibility is loose or corroded connections. Also make sure to remove both battery terminals and check that they are clean. Make sure too that you don't have an under drive pulley. You don't want the belt too tight either.
I prefer to find a local and reputable starter and alternator re-builder that you can bring yours in and have them rebuild it. You can also get a core at a junk yard so you have something to use while it's being repaired. It's nice to have an extra around for times when your voltages are telling you it needs to be replaced and you can just walk over and grab what you need on the spot.
-hope that helps.
With the engine off, you're reading the resting battery voltage. That should be around 12v or a little less.
While running IIRC it's around 14.4, but if it goes over 15.5 it's overcharging and can damage or cook your battery. You would also notice that your headlights and interior lights are brighter than normal.
(The alt blindly generates as much as it can while the regulator limits the upper limit. That said, the regulators are often inside of the alternator anyway. But you can disassemble it to replace it if you want.)
Many people make the mistake of simply checking once and letting it go at that. Or, maybe taking it in to get it checked, but it's my opinion that you can more effectively check both the alternator and battery with a meter and sometimes with a home made lead that plugs into a cigarette lighter. The actual voltage may be slightly less doing it this way, but not enough to have any meaningful value.
If the voltages checks out at rest and while running from the engine bay, then you would use the cig lighter lead to check the voltage while starting. If it drops from say 11v to less than 9, the battery does not have enough capacity. The lead that I mentioned can also be used while driving so you can know the exact voltages when those symptoms occur, and you'll also know about where the needle is on the cluster gauge for various voltages. With what you are describing I'm guessing that when it gets clsoe to stalling you'll see something around 13v and often at 12v which will mean that your car is running off of the battery.
Yes you can bring in both the battery and alternator to get them load tested but you already have load testers in the car itself. What this does is it includes your connections (good or bad), and also includes how the various operating temperatures like heat or cold affect your system. Or even if something were to vibrate loose or move affecting your connection.
What I think you have is a failing alternator. You can verify this by watching the voltage with the car running and then turning on and off headlights and other accessories. As the alternator wears out it isn't as efficient and can't produce as much as it used to. Another possibility is loose or corroded connections. Also make sure to remove both battery terminals and check that they are clean. Make sure too that you don't have an under drive pulley. You don't want the belt too tight either.
I prefer to find a local and reputable starter and alternator re-builder that you can bring yours in and have them rebuild it. You can also get a core at a junk yard so you have something to use while it's being repaired. It's nice to have an extra around for times when your voltages are telling you it needs to be replaced and you can just walk over and grab what you need on the spot.
-hope that helps.
10-18-2015, 12:21 PM
#9
Re: Low voltage until I WOT
I don't recall the exact voltages off hand but I've posted them many times before if you want to try to search.
With the engine off, you're reading the resting battery voltage. That should be around 12v or a little less.
While running IIRC it's around 14.4, but if it goes over 15.5 it's overcharging and can damage or cook your battery. You would also notice that your headlights and interior lights are brighter than normal.
(The alt blindly generates as much as it can while the regulator limits the upper limit. That said, the regulators are often inside of the alternator anyway. But you can disassemble it to replace it if you want.)
Many people make the mistake of simply checking once and letting it go at that. Or, maybe taking it in to get it checked, but it's my opinion that you can more effectively check both the alternator and battery with a meter and sometimes with a home made lead that plugs into a cigarette lighter. The actual voltage may be slightly less doing it this way, but not enough to have any meaningful value.
If the voltages checks out at rest and while running from the engine bay, then you would use the cig lighter lead to check the voltage while starting. If it drops from say 11v to less than 9, the battery does not have enough capacity. The lead that I mentioned can also be used while driving so you can know the exact voltages when those symptoms occur, and you'll also know about where the needle is on the cluster gauge for various voltages. With what you are describing I'm guessing that when it gets clsoe to stalling you'll see something around 13v and often at 12v which will mean that your car is running off of the battery.
Yes you can bring in both the battery and alternator to get them load tested but you already have load testers in the car itself. What this does is it includes your connections (good or bad), and also includes how the various operating temperatures like heat or cold affect your system. Or even if something were to vibrate loose or move affecting your connection.
What I think you have is a failing alternator. You can verify this by watching the voltage with the car running and then turning on and off headlights and other accessories. As the alternator wears out it isn't as efficient and can't produce as much as it used to. Another possibility is loose or corroded connections. Also make sure to remove both battery terminals and check that they are clean. Make sure too that you don't have an under drive pulley. You don't want the belt too tight either.
I prefer to find a local and reputable starter and alternator re-builder that you can bring yours in and have them rebuild it. You can also get a core at a junk yard so you have something to use while it's being repaired. It's nice to have an extra around for times when your voltages are telling you it needs to be replaced and you can just walk over and grab what you need on the spot.
-hope that helps.
With the engine off, you're reading the resting battery voltage. That should be around 12v or a little less.
While running IIRC it's around 14.4, but if it goes over 15.5 it's overcharging and can damage or cook your battery. You would also notice that your headlights and interior lights are brighter than normal.
(The alt blindly generates as much as it can while the regulator limits the upper limit. That said, the regulators are often inside of the alternator anyway. But you can disassemble it to replace it if you want.)
Many people make the mistake of simply checking once and letting it go at that. Or, maybe taking it in to get it checked, but it's my opinion that you can more effectively check both the alternator and battery with a meter and sometimes with a home made lead that plugs into a cigarette lighter. The actual voltage may be slightly less doing it this way, but not enough to have any meaningful value.
If the voltages checks out at rest and while running from the engine bay, then you would use the cig lighter lead to check the voltage while starting. If it drops from say 11v to less than 9, the battery does not have enough capacity. The lead that I mentioned can also be used while driving so you can know the exact voltages when those symptoms occur, and you'll also know about where the needle is on the cluster gauge for various voltages. With what you are describing I'm guessing that when it gets clsoe to stalling you'll see something around 13v and often at 12v which will mean that your car is running off of the battery.
Yes you can bring in both the battery and alternator to get them load tested but you already have load testers in the car itself. What this does is it includes your connections (good or bad), and also includes how the various operating temperatures like heat or cold affect your system. Or even if something were to vibrate loose or move affecting your connection.
What I think you have is a failing alternator. You can verify this by watching the voltage with the car running and then turning on and off headlights and other accessories. As the alternator wears out it isn't as efficient and can't produce as much as it used to. Another possibility is loose or corroded connections. Also make sure to remove both battery terminals and check that they are clean. Make sure too that you don't have an under drive pulley. You don't want the belt too tight either.
I prefer to find a local and reputable starter and alternator re-builder that you can bring yours in and have them rebuild it. You can also get a core at a junk yard so you have something to use while it's being repaired. It's nice to have an extra around for times when your voltages are telling you it needs to be replaced and you can just walk over and grab what you need on the spot.
-hope that helps.
10-18-2015, 01:34 PM
#10
Re: Low voltage until I WOT
weird. I hook up my volt meter to the battery and got 12 volts with the car off, then when I start her up the dash reads a perfect 13-14 and so does the volt meter. The ONE day I go to test voltage and the car is perfectly fine, looks like I'll have to wait till next weekend
10-18-2015, 05:15 PM
#12
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Re: Low voltage until I WOT
wow that is more information than I could have ever asked for. thank you for taking the time to write that up. No under drive pulleys and when I do turn on the headlights/heater/etc my volts drop down to around 10 while idling, itll shoot up to around 11.5/12 while driving based on the dash gauge. I figured that was normal for these cars. I also noticed today that the positive connection on the battery has a crack on the red plastic. I'm thinking I'm gonna run to autozone and see If I can pick one up as well as a volt tester since mine is lost somewhere in my shed.
weird. I hook up my volt meter to the battery and got 12 volts with the car off, then when I start her up the dash reads a perfect 13-14 and so does the volt meter. The ONE day I go to test voltage and the car is perfectly fine, looks like I'll have to wait till next weekend
No, that's not normal at all. Even 13 is a bit low imo. Also, did you try turning on the high beams and AC the second time to see if the additional load brings it down farther?
10-18-2015, 06:29 PM
#13
Re: Low voltage until I WOT
high beams didn't even cross my mind, on my way to work tomorrow morning I'll get an accurate number on how much volts it drops with high beams/heater/defroster. If i recall correctly it will end up at around 10 volts.
10-18-2015, 08:53 PM
#14
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Car: 85 SC, 86 Berlinetta
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Re: Low voltage until I WOT
IMO, the alternator needs to be rebuilt or replaced.
Here is a video that may help, I'm only referring to the first part.
10-18-2015, 11:34 PM
#15
Re: Low voltage until I WOT
It shouldn't ever drop to 10volts. It may momentarily dip when a load is added, but the voltage should go back to 14.4 or so.
IMO, the alternator needs to be rebuilt or replaced.
Here is a video that may help, I'm only referring to the first part.
How to Test an Alternator - YouTube
IMO, the alternator needs to be rebuilt or replaced.
Here is a video that may help, I'm only referring to the first part.
How to Test an Alternator - YouTube
10-19-2015, 05:30 AM
#16
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Car: 85 SC, 86 Berlinetta
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Re: Low voltage until I WOT
Probably should clarify that my fan is wired to constantly run and these volt drops are when the cars sitting at idle if that makes a difference. Let's say I have no accessories on and my volts are at 14, if I come to a complete stop and put ac/headlights/defroster on it will drop to around 10, once I take off again it will rise to around 12-12.5. Is that still not normal? Even with all those accessories should my car still maintain 13-14 volts at idle?
The fan could be drawing excessive power so you might want to try disconnecting that to see how much of a difference that makes.
10-19-2015, 06:39 AM
#17
Re: Low voltage until I WOT
No that is not normal. Anything under 12v is running off of the battery and leading to its demise. Yes, it should try to maintain 14.4, anything closer to 13 isn't that great, since as in the video, the battery will often sit at 12.5 or higher.
The fan could be drawing excessive power so you might want to try disconnecting that to see how much of a difference that makes.
The fan could be drawing excessive power so you might want to try disconnecting that to see how much of a difference that makes.
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