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Charging problems with Underdrive pulleys ? Try this.

5K views 8 replies 5 participants last post by  EL1XR8 
#1 · (Edited)
If you have underdrive pulleys, and are experiencing charging problems when idling, this might help a little. On my EL XR8 (so I guess all other E series V8’s must be similar?) the alternator pulley is about 60mm diameter (measured at the top of the ribs). The AU 6 cylinders (and maybe V8’s too, I’m not sure) have an alternator diameter of about 52mm (again measured at the top of the ribs, not on the outside flanges). These pulleys are interchangeable, in every other aspect (i.e bore diameter, spigot length, belt type etc), so if you swap these over, you’ll speed up your alternator by about 15%. Not quite as much probably as the amount you originally slowed it down (in my case about 25%), but this seems to help.

A few tips if you decide to do this. Firstly, don’t by new from Ford ($150+), try a wreckers or auto electrician instead ($10-$20). Secondly, you’ll need a rattle gun to remove the nut securing the pulley on the alternator. In my case I still had enough adjustment left on the automatic belt tensioner to take up the slack or the reduced diameter, but this is something you’ll also need to check.

I didn't notice any loss in power with this, as you still have your waterpump and power steering running slower.
 
#2 ·
A good suggestion EL1XR8. The alternator is not hard to turn so gearing it up a little would not really hinder the effect of the underdriven crank pulley. The smaller diameter alternator pulley would also help the fact that the tensioner is at its maximum travel.
 
#3 ·
Ah, bloody excellent suggestion EL1XR8. I have noticed that at idle my car battery sits at 10V and when driving it sits at 12. I was starting to think that maybe my alternator is cactus...

So does the underdrive pulley slow the rate of charge of your alternator and does the AU one give you a better charge? What charge do you now get?

Cheers.

Getting a big sound system soon and I don't want to have any power problems. :)
 
#6 ·
I agree that if your voltage is sitting on 12V when cruising, then i think that swapping your alt pulley will not fix your problem. It should be around 14V (well thats what i seem to sit around).

In my case (previous to putting the smaller alt pulley on) the volts would drop down around 10-10.5 if you had all the electrical accessories on at idle. You didn't need to increase the revs much to start to get a much higher charge. This AU pulley change has not completely fixed the problem (really you need to go even smaller, but i didn't want to mess around with a one off custom one, as these AU pulleys seem easy enough to get a hold of), but now it only drops to about 11.5 (if you have everything on), or only a tiny amount of throttle is required to bring the idle up enough to bring the charge above 12V. In any event, i generally avoid loading the electrical system up too much when idling now anyway, so it hasn't created any issues for me.
 
#7 ·
I am having the same probles too but am just putting up with it, it's only at idle so it's not a big problem. If you are worried, Barry does different sized alternator pulleys to speed it up. Don't know if they are cheaper than the AU ones and what sizes are available.
 
#8 ·
Hmm, so what do you guys think I should do? I mean, I am going to be having quite an expensive car audio setup eventually and I will want enough power for it!

EL1XR8, my car is behaving the same in that you only need to press the pedal a little for the charge to go up.

Does the alternator need replacing or do I need to play with pulleys?
 
#9 ·
If you are getting sufficient charge once the revs increase a bit above idle, i would not think that you have an alternator problem. I have had these pulleys on for over 12 months now, and have never got into any situations where the lower charge at idle created any major issues. Having said that, i rarely get caught in heavy traffic, so if you do (and its hot), then you might need to try a smaller alternator pulley, as when your engine cooling fans come on, they would draw a fair bit of power.

It was only that i noticed while servicing an AU that the AU alternator was smaller, so i thought it might help a little. Its helped a bit for me anyway, and for the price, it was a cheap improvement.
 
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