Dreaded Alternator Issue

[G00nies]

Yes...my car came with under drive pulleys installed (unbeknownst to me until now)
1992 Mustang GT 5.0L

Yes, ive since rewired both harnesses and replaced with NEW 75amp stock alternators. They last 6 months before the battery light returns.

I need two things:

Where to find a stock set of pulleys for my car that don't cost a fortune

and

I've been told that a 130 amp alternator from certain 96-99 E/F series trucks with the 4.9L engine are compatible with my 5.0?Is this true?

 

[General karthief]

There is a sticky thing up top that has info on the 3g alt swap, you could look there or I could summon @jrichker to use his powers to post the thing here. I don't think he really minds, after all, he is one of the resident geniuses here.
Yes I'm still suck'n up.

 

[Mustang5L5]

3G or 6g Alts will work. 6G has a smaller case, but wiring is the same.

Keep in mind, you issue isn't amps, but proper rpm needed to begin generating full power. Either install an ASP overdrive alt pulley first, or reinstall stock pullies, before changing the alt.

 

[Mustang5L5]

https://www.autospecialties.com/ford.html


Bottom of page. Google the part number for cheapest source. I have a 1 7/8" pulley on mine with unferdrive crank. No charging issues with 3G alt and e fan

 

[G00nies]

https://www.autospecialties.com/ford.html


Bottom of page. Google the part number for cheapest source. I have a 1 7/8" pulley on mine with unferdrive crank. No charging issues with 3G alt and e fan

Thanks

 

[stpete]

LMR sells a full set of stock pulleys for $99. They often have sales on all their LMR or 5.0 resto parts, I think I paid like $75 on a sale. Everything electrical, and cooling got much better when I got rid of the damn underdrive pulleys totally. I did like the PS better underdriven though.

 

[Mstng93SSP]

I have never had any luck with underdrive pullies. I have bought a few cars with them already installed and it was the first thing I took off. Overheating, no charging, useless on a street car. If anyone tells you they run under drives with no charging issues and no overheating while sitting in traffic I would be very suspicious... Get some stock pullies either from classifieds on here or corral.net, or look in a junkyard. Then you can have piece of mind by also doing a 3g alternator upgrade. I have 3g on both my cars.

 

[Mustang5L5]

I. Overheating, no charging, useless on a street car. If anyone tells you they run under drives with no charging issues and no overheating while sitting in traffic I would be very suspicious...

I've had them on my car since 1997 or so, and I've never had cooling or charging issues. Granted, i've made modifications to those two areas so to not have a problem...

 

[Mstng93SSP]

What alternator and what's your average outside temperature? Here in Hawaii, sitting in 2 hours of traffic at 90 degrees with underdrives you are done....

 

[Mustang5L5]

Short summer, but we peak around 95-100 in Aug. I don't run A/C though. But years ago when the car was a daily driver, I spent plenty of time sweating my butt off in traffic when 90+.

Since I'm reinstalling the AC, I'll prob toss the stock puppies back on as I'd prefer some extra reliability these days

 

[mikestang63]

Any alternator from a 94-95 mustang will work- you just need to notch the sotck alternator bracket a bit for clearance. For stock pullies. check craiglist and the corral for guys parting out cars.

 

[JD1964]

http://www.ebay.com/itm/1987-1993-f...ash=item23750acb8d:g:h6cAAOSwn7JYCB2l&vxp=mtr

 

[G00nies]

https://www.autospecialties.com/ford.html


Bottom of page. Google the part number for cheapest source. I have a 1 7/8" pulley on mine with underdrive crank. No charging issues with 3G alt and e fan

How do I interperate the percentages on the pulley chart on the ASP website?

 

[Mustang5L5]

How do I interperate the percentages on the pulley chart on the ASP website?

Percent reduction from stock rotation speed.

How big is your alt pulley now? 2" What size is your crank pulley?


You can also do some basic math.
If your crank pulley is 4" in OD, then that's a 25" circumference. So if your alt pulley is 2", that's 12.5" of circumference. So literally a 2:1 ratio. That means if your are idling at 800RPM, your alt is spinning 1600RPM.

What min RPM is needed all depends on the alternator itself.

Lets say you swap on the 1 7/8 OD pulley from ASP on the alt. That would give you an alt RPM of 1700RPM. Only 100 RPM or so more, but getting closer to where you need to be.

 

[G00nies]

So i just measured my crank pulley and it is 4.75" and the alternator pulley is 2" and the idle is between 700-800 rpm

 

[Mustang5L5]

So that's 1788 RPM with an idle of 750 and the 2" pulley.

Or 1910RPM if you install an ASP 1 7/8" overdrive alt pulley.

Only a difference of 125 RPM, but you'll have to do a little testing with a DMM to determine if that is enough RPM.

 

[General karthief]

I'm ditch'n my underdrives and do'n the 3g thing, I hate math.

 

[Mustang5L5]

I'm ditch'n my underdrives and do'n the 3g thing, I hate math.

Same problem.

I had a weblink that had the minimum RPM many alts needed to make full power. I do know the 3G was one of them, but can't recall the RPM.

I do know with underdrives, and that overdrive alt pulley, I can sit at idle, with a 3G alt with my SN95 e-fan blowing away without issue.

 

[G00nies]

So that's 1788 RPM with an idle of 750 and the 2" pulley.

Or 1910RPM if you install an ASP 1 7/8" overdrive alt pulley.

Only a difference of 125 RPM, but you'll have to do a little testing with a DMM to determine if that is enough RPM.

I think I understand now. I can install the ASP pulley kit 520124 (1 7/8 alt, 15% WP and 25% crank)with my current stock 75A alternator and fine tune from there, OR, install a 3G alternator and do the wiring to make it work properly and not have to mess with the underdrives/overdrives?

Could I leave the ASP520124 kit INSTALLED when I swap to the 3G? Or is it the same formula?

Im just sick of alternators burning up, also sick of anemic power supply

 

[stpete]

I saw the RPM vs. power stuff you were talking about and chose my replacement alternator because it made good power at lower RPMs. But, mine was still right on the verge. If the car was idling properly, my 3G with underdrives would make enough power even with the e-fan on. But, if the car had issues and the idle started hunting around it would sometimes drop below the threshold and make things worse. Going back to stock pulleys kept the car from stalling as things weren't quite right with the car and I chased my way through the idle checklist. To be blunt, I think underdrives suck, 3G or not.