Just installed Powerbond UDP, now alternator is not working?
Thread Starter
Joined: Apr 2005
Posts: 361
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From: Huntington, WV
Just installed Powerbond UDP, now alternator is not working? Well after a PITA pulley install everything started out ok, car started and ran good, no squeals or thrown belts, but I noticed my battery seemed waeker. The gauge was low and windows were slower. I unhooked the positive battery terminal with it running and it died... So I checked everything again, belt routing is correct, everything is plugged up correctly. Did my alternator jsut take a **** concidently at the same time as I did this pulley swap or did the swap kill it/affect it. I swapped the harmonic balancer only, 25% underdrive, did not do alternator pulley.
Thread Starter
Joined: Apr 2005
Posts: 361
Likes: 0
From: Huntington, WV
I did some searching, udp's can cause slow charging? You can correct this with a overdrive alt pulley? Will I need a different belt than the one for the ud crank pulley only? Some help here would be greatly appreciated.. thanks
Thread Starter
Joined: Apr 2005
Posts: 361
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From: Huntington, WV
After even more searching old threads I am more confused than ever. Some say you need an underdrive alt pulley, some say you need an overdrive alt pulley...? There are apparently issues of bolts interfering with the belt when you change alt pullies. You can apparently fry an alternator when you do an underdrive crank pulley swap according to some? What the hell? I dont have a system, my car is a M6. There is def a difference after this pulley swap, my alt was not working at all hence the car dying at idle when I unhooked the battery. My car is tuned to idle 500-600. Please help I appreciate it 
Mine did the same thing after I did the 25% UD pulley. Usually it only affects the a4 guys, but you either need an overdrive alt pulley, or raise your idle rpms. If I'm not mistaken, our alts need around 800 rpm to keep charging. I bumped my idle rpm up to 875-900 and the voltage has been more normal. Not perfect, but almost normal.
I wouldn't think that it would cancel out the gains, since all it's doing is making the alternator spin faster. If it does cancel out anything, it definitely shouldn't be the full gain of putting the UDP on in the first place. Since you're an M6, just try keeping your foot on the gas at idle until your RPMs are around 800-1000 to see if the voltage acts normal before you buy anything. That will at least help you identify if the problem is from the changed RPM of the UD pulley.
Thread Starter
Joined: Apr 2005
Posts: 361
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From: Huntington, WV
Ill try that later today. Ill get the rmps up around 1000 and then disconnect the battery again to see if the alternator is working then. I am also considering getting a 99-04 truck 145 amp alt. Any other suggestions?
Last edited by b0b; Jul 24, 2012 at 05:29 AM.
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Joined: Jun 2007
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From: Westminster, MD
No it won't cancel out all gains because everything else will be more efficient but an ODP for the alternator is definitely a good idea. If you really want to make it efficient get an electric water pump too if you can afford it.
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Brett Foote I was able to tell just by watching the voltage gauge. I knew it was the RPMs because when I was driving, the voltage would drop at a stop light, and my lights would dim, then it'd go back to normal when I started moving again (800+ RPM). The truck alternator is a good budget option if you do suddenly have a bad alternator, but I doubt that's the problem.
Even my stock setup used to sag voltage when I had the
A/C on in the summer. Running it slower helps none; you
sit on the thermal limit of the alt's regulator, throwing field
current to make up for loss of shaft RPM at net zero gain
but more heat in the guts.
Running your fans at lower temp can help. Bumping up
idle RPM to something like 700-750 could help (at least
by as much as you underdrove the alt). Cleaning your rad
so you get more cooling airflow and less cooling air temp
rise to cook the engine bay can help. And of course the
alt overdrive pulley can get that piece back to normal
by itself.
A/C on in the summer. Running it slower helps none; you
sit on the thermal limit of the alt's regulator, throwing field
current to make up for loss of shaft RPM at net zero gain
but more heat in the guts.
Running your fans at lower temp can help. Bumping up
idle RPM to something like 700-750 could help (at least
by as much as you underdrove the alt). Cleaning your rad
so you get more cooling airflow and less cooling air temp
rise to cook the engine bay can help. And of course the
alt overdrive pulley can get that piece back to normal
by itself.
The Powerbond pulley and the SLP pulley are the same piece...SLP just charges more for it under their name. And yes, this correlates...hopefully he knew he had to change to smaller belts.
