NST Pulley Set Alternator Issue

[MGargano]

I picked up and installed a full set of NST pulleys a little over a year ago. To my knowledge, they were not underdrive or overdrive pulleys, just the lightened version, but apparently (thanks to CTScott's diagnosis) my alternator is under-charging the battery.

I'm not sure if this is a new issue or if it has been doing this for the past year- either way, I'm curious why/how the non-underdrive pulley set could be causing this.

When running, the ScanGauge puts my voltage at 14.1 maximum, without any kind of load (amplifiers, head unit, etc.). Even 14.1 is rare- it's usually around low- to mid-13's.

I did a search and saw some people having the same problem with the 10% underdrive pulley, but I'm curious if anyone has run into this with the standard lightened set and what a potential fix might be. Something as simple as tightening the belt? Or something more drastic?

[1NZYaris1]

Simple solution , put the OEM pullie back on and retest , i bet you will
finf it is the Alternator that is Fualty ,and it will have nothing to with the Pullies .
It might also pay to check all connections betwen the alternator and the battery .
Aswell as the battery main fuse.

[MGargano]

Originally Posted by 1NZYaris1

Simple solution , put the OEM pullie back on and retest

Should I replace all three pulleys with OEM? Or just the crank pulley?

[1NZYaris1]

Just The Crank

[shinlee]

I've got all 3 pullies on for over 2 years, never, not once, have I had a problem with my alternator, and thats with 3 subs in the car too.

Alternator is going out, no biggie, but it's not the pullies fault

[MGargano]

Originally Posted by shinlee

I've got all 3 pullies on for over 2 years, never, not once, have I had a problem with my alternator, and thats with 3 subs in the car too.

Alternator is going out, no biggie, but it's not the pullies fault

I wasn't really blaming the pulley for doing anything wrong- I'm more curious to know if I received the correct one and/or if it was installed correctly by the shop I took it to.

For instance, if I received a 10% underdrive pulley by mistake, that would explain the lower voltage I'm seeing. Would a loose belt do the same thing?

[goliath1812]

Even with the 10% underdrive pulley set, I thought there were still supposed to be no issues with under-charging...?

[MGargano]

Originally Posted by goliath1812

Even with the 10% underdrive pulley set, I thought there were still supposed to be no issues with under-charging...?

That's what I thought too, but I'm hoping for some confirmation so I can rule out the pulleys as the problem. I don't want to go through the hassle of putting the OEM pulley back on if it turns out to be a bad alternator.

I'm guessing a max of 14.2v while moving at speed with no load is considered "low"?

[lilredrocket]

Just size up your stock pulley to your NST one if the one on your car is smaller than stock you have the under drive one.

[MGargano]

Originally Posted by lilredrocket

Just size up your stock pulley to your NST one if the one on your car is smaller than stock you have the under drive one.

Just checked- the two pulleys are identical in diameter, so I guess I have the right one installed, not the underdrive.

I guess that leaves the alternator as the culprit?

[Bluevitz-rs]

What's the voltage @ 2500-3000 rpm? and how many miles/km on it?

[MGargano]

Mileage is 10,906.

Voltage with no load at 3,000rpm is 14.1v- but it definitely does not hold that voltage while driving. It fluctuates, but usually hovers in the low- to mid-13's

[Bluevitz-rs]

That's about normal

[shinlee]

with the car on, normal output should be 13.7 to 14.5

with the car off, the battery should be about 12.5

I used to manage an Autozone, and I've done god knows how many alternator checks. If you're getting 14.1 then you should be fine. It sounds to me like there may be an issue in the wires, something not connected properly or something of that sort. A loose (incredibly loose) belt will cause it to not charge properly, but just pull on the belt while it's off, and if there's a lot of play, either tighten it up or replace it.

[MGargano]

Originally Posted by shinlee

with the car on, normal output should be 13.7 to 14.5

with the car off, the battery should be about 12.5

The battery holds at ~12.5v when off, but the "normal output" for me is lower than 13.7- usually closer to 13.2-13.4. I'm not sure if those 1/10's of a volt are a cause for concern, really.

Originally Posted by shinlee

If you're getting 14.1 then you should be fine

It doesn't hold steady at 14.1 for any extended length of time- low 13's are "normal" for me

Originally Posted by shinlee

A loose (incredibly loose) belt will cause it to not charge properly, but just pull on the belt while it's off, and if there's a lot of play, either tighten it up or replace it.

I inspected the belt when I compared the pulley sizes- it was nice and tight, no play or slack at all.

[severous01]

if you buy the underdrive set isnt the alternator smaller to compensate and it's actually over-driven?

my experience with underdrive kits any way...jsut the alternator, not pump or any others, jsut the alternator to compensate for slower belt speed

[cruz-gsr]

thats what i normally get on mine

[MGargano]

I tightened the belt very slightly last night and today everything seems to be "normal"- between 13.7 and 14.2.