Alternator dropping voltage at WOT only?
Thread Starter
Joined: May 2011
Posts: 8,485
Likes: 1,028
From: Wichita, KS
Alternator dropping voltage at WOT only? Recently had my alternator start dropping voltage at WOT. It basically stops charging anytime I'm making a pass. Then it charges fine when I lift/cruise/idle? I had a resitor inline with the alternator field wire. I since replaced the alternator and installed a check engine style bulb inline instead of the resistor. Car acts the same. I see 14v+ on startup, drops to 13.3 after a long cruise and down to the low 12's when I get on the throttle?
I also have a new belt and tensioner. This combo and belt wrap routing has been working great for about 5 years now always had 13.6v or so WOT. I see no dust of evidence of belt slip. It just quits charging...
Here is a log. Bottom graph redline (looks like steps). Anyone have this issue before?
This is a 6lb pull and voltage drops to 12.9. If I up the boost to 13+lbs it drops to 12.2v...
I also have a new belt and tensioner. This combo and belt wrap routing has been working great for about 5 years now always had 13.6v or so WOT. I see no dust of evidence of belt slip. It just quits charging...
Here is a log. Bottom graph redline (looks like steps). Anyone have this issue before?
This is a 6lb pull and voltage drops to 12.9. If I up the boost to 13+lbs it drops to 12.2v...
Last edited by Forcefed86; Aug 31, 2016 at 09:52 PM.
Both times my alternator went out, it happened after
some similar romping. Consider yourself lucky that it
comes back on line, and start shopping for a good
truck 145 alternator (I got mine at a bone yard, so
far so good).
You can check the L terminal connector and wire
(mine broke off with no effort at all during the swap)
but I think there's something internally wrong with
the OE alternator design. Be prepared.
some similar romping. Consider yourself lucky that it
comes back on line, and start shopping for a good
truck 145 alternator (I got mine at a bone yard, so
far so good).
You can check the L terminal connector and wire
(mine broke off with no effort at all during the swap)
but I think there's something internally wrong with
the OE alternator design. Be prepared.
I fought this for awhile. The regular high speed runs I had been making to tune the car was over spinning the alternator. I tried a truck alternator but that didn't help me.
I ended up using a larger 2.75" alternator pulley (with a rebuilt alternator) and tweaking my idle RPM a bit so it had the same idle charging output.
I ended up using a larger 2.75" alternator pulley (with a rebuilt alternator) and tweaking my idle RPM a bit so it had the same idle charging output.
Thread Starter
Joined: May 2011
Posts: 8,485
Likes: 1,028
From: Wichita, KS
Thanks for the input. I can’t see that being the issue. I’ve used the same crank pulley and pulley diameter in the past and had zero issues for 3 years.
I have a feeling my old alternator fried (was 3 years old and an auto zone reman) I had a free replacement warranty and I’m wondering now if autozone gave me the incorrect 2 wire alternator for the 99 and up F-bodies, and not the 1 wire alternator for the 98 f-body. Is there any way to tell the difference by looking at it?
I have a feeling my old alternator fried (was 3 years old and an auto zone reman) I had a free replacement warranty and I’m wondering now if autozone gave me the incorrect 2 wire alternator for the 99 and up F-bodies, and not the 1 wire alternator for the 98 f-body. Is there any way to tell the difference by looking at it?
"The only known factory LS application where the stock ECU doesn’t connect to the alternator is the ’98-’02 F-body. However, most of the “computer controlled” alternators on these engines can be placed in an automatic mode by wiring their “L” terminal to the dashboard alternator warning light (which would get switched 12 volt power if your car originally did not have one). When the L terminal is connected to a lamp, the alternator will power up and put out charging voltage. This trick works on any alternator with a four terminal connector where the terminals are marked P, L, F (or F and I on the same terminal), and S. The remaining three terminals are left disconnected."
CC alts cut out charging at WOT tps voltage. Even if yours is "bad" its still not a "bad" thing.
CC alts cut out charging at WOT tps voltage. Even if yours is "bad" its still not a "bad" thing.
I was fighting alternator issues for the past 2 months. I went through 3 brand new alternators from DB Electrical and finally ended up going with their Truck style alternator for the Escalade's and haven't had an issue yet!
I have lots of nitrous electrical components on my car and after every time I took the car out to test (WOT Nitrous Passes) the alternator would die on the way home... I figured the stock size alternator just wasn't sufficient for all the extra electronics I was running. I was even having issues with my solenoids at high RPM and that went away with the bigger alternator. I believe the oem Fbody alternator is 90amps whereas the truck style is 145.
If anything you will want a larger pulley rather than a smaller one to help with high RPM.
I have lots of nitrous electrical components on my car and after every time I took the car out to test (WOT Nitrous Passes) the alternator would die on the way home... I figured the stock size alternator just wasn't sufficient for all the extra electronics I was running. I was even having issues with my solenoids at high RPM and that went away with the bigger alternator. I believe the oem Fbody alternator is 90amps whereas the truck style is 145.
If anything you will want a larger pulley rather than a smaller one to help with high RPM.
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Forcefed - did you ever figure this out? Mines doing the same thing. Charges 13.8-14.0 at idle and cruising, then drops to 11.7-12.0 at WOT. I also have a Powermaster 225Amp truck-style AD244 alternator, with a larger diameter pulley recommended by Powermaster.
I'm using Holley EFI, with the holley 1-wire alternator pigtail with resistor in-line.
I'm using Holley EFI, with the holley 1-wire alternator pigtail with resistor in-line.
Thread Starter
Joined: May 2011
Posts: 8,485
Likes: 1,028
From: Wichita, KS
I installed a self-exciting 160a alt and it fixed my issue. I tried the 100a self-exciting unit first and it did the same thing. I assumed it was an amperage drop thing in my case. Sounds like your alternator should be more than enough for the job.
If you have the ability to turn the E-fan off under WOT conditions it helps. (esp if you have a 30-40a fan like I do) Getting by with a 100a self-exciting Alt on my new build doing this. Good luck!
If you have the ability to turn the E-fan off under WOT conditions it helps. (esp if you have a 30-40a fan like I do) Getting by with a 100a self-exciting Alt on my new build doing this. Good luck!
Powermaster did say that I could run the alternator without a pigtail at all. Does that mean it is self-exciting?
Yes, I can turn off the fan, but why would it drop from 13.8 to 11.8 just because of WOT? It's an instant drop too, as soon as the throttle hits 100%. Nothing else is turning on at wot that would draw any extra amps.
Yes, I can turn off the fan, but why would it drop from 13.8 to 11.8 just because of WOT? It's an instant drop too, as soon as the throttle hits 100%. Nothing else is turning on at wot that would draw any extra amps.
Thread Starter
Joined: May 2011
Posts: 8,485
Likes: 1,028
From: Wichita, KS
No idea on your setup, it likely shouldn’t. In my case I had my voltage booster for the fuel pump and alky inj coming on that loaded up the alt more. What ECU are you using? Is it dropping the alt field voltage at WOT? Might put a meter on it and see.
It's a dominator ecu. Not sure on the field voltage. I noticed it when my 4303 magnafuel pump started dropping pressure. I didn't think I was near it's max yet, then looked at the datalogs and saw the voltage drops at wot, then pops right back up to 13.8 when the throttle is lifted.
Thanks for the help. I'll mess around with it. The first thing I'll probably do is increase the wire size from the alternator back to the battery. It's currently only 4 gauge. Probably needs 1 gauge, since there's 15 feet of it.
Thanks for the help. I'll mess around with it. The first thing I'll probably do is increase the wire size from the alternator back to the battery. It's currently only 4 gauge. Probably needs 1 gauge, since there's 15 feet of it.
Every tenth of a volt in these low voltage systems counts.
I fixed my issues by switching to a Powermaster 150A alt 14.7v alt, 4ga charge wire, HD relays for the pumps and another HD relay to power the pcm. I'm using the GM ecu. I also changed the batt cutoff switch.
One thing you can do is test at idle with everything running and drawing max current. So use a mighty vac on the regulator to simulate boost (might **** of the plugs) and measure voltage to the tenth starting at the alternator checking every point you can along the way.
Another possibility could be the battery itself. They can have internal plate issues under hard acceleration. Just a thought.
Lastly, check all grounds. Engine grounded to the frame? Batt ground good and tight and clean? Etc.
My buddies car that I tune is doing the same. So I'm going to have to go through it as well. His uses the truck alternator.....and has two leads in the plug connected. I need to research that. Mine is Camaro based.
I'm 100% sure his high injector duty cycle is caused by low volts at the pump.
Ron
I fixed my issues by switching to a Powermaster 150A alt 14.7v alt, 4ga charge wire, HD relays for the pumps and another HD relay to power the pcm. I'm using the GM ecu. I also changed the batt cutoff switch.
One thing you can do is test at idle with everything running and drawing max current. So use a mighty vac on the regulator to simulate boost (might **** of the plugs) and measure voltage to the tenth starting at the alternator checking every point you can along the way.
Another possibility could be the battery itself. They can have internal plate issues under hard acceleration. Just a thought.
Lastly, check all grounds. Engine grounded to the frame? Batt ground good and tight and clean? Etc.
My buddies car that I tune is doing the same. So I'm going to have to go through it as well. His uses the truck alternator.....and has two leads in the plug connected. I need to research that. Mine is Camaro based.
I'm 100% sure his high injector duty cycle is caused by low volts at the pump.
Ron
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Joined: Nov 2003
Posts: 13,616
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From: Norn Iron
I would be surprised if the voltage drops at WOT alone....more probably at high rpm ? and/or WOT
Saying it does it at WOT implies at any load, any conditions but full throttle it stops charging ?
Saying it does it at WOT implies at any load, any conditions but full throttle it stops charging ?
I don't have my laptop with me, or I'd take a screenshot, but no, it drops instantly at WOT, then pops back up instantly once the throttle is lifted.
It is not tied to the computer in any way: just the main 4awg power cable and the 1 wire w/ resistor going to a switched ignition power source.
It is not tied to the computer in any way: just the main 4awg power cable and the 1 wire w/ resistor going to a switched ignition power source.
Not to ask a dumb question but how tight is your belt?
When my motor got really responsive I kept slipping the alternator belt at WOT causing loss of charging voltage. Deleted factory tensioner and went with Jegs manual alternator tensioner. Banjo tight gator back belt. I can spin the engine from the alternator pulley. Problem solved.
When my motor got really responsive I kept slipping the alternator belt at WOT causing loss of charging voltage. Deleted factory tensioner and went with Jegs manual alternator tensioner. Banjo tight gator back belt. I can spin the engine from the alternator pulley. Problem solved.
Restricted User
Joined: Mar 2014
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From: Ohio
Could've been duty cycle related. Alternators running at 100% duty cycle typically charge at less voltage than alternators at 80-90% duty cycle. High RPM can cause the voltage to drop even further depending on the alternator.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
But he isnt saying it is rpm related, only throttle...full throttle ?