do you have underdrive pullies?

I did the 3g on my fox and noticed a huge difference at idle and when driving.  Used alt from 94 or 95 mustang, 130 amp.  had to grind some metal away on the bracket to make it fit.  It is the smaller case model.  Used a megafuse and wired it directly to the battery.

Heres a close up of
G install a few years ago.   I took the serpentine pulley off and installed a V pulley.    I had to extend the lower alternator bracket also. Steve69

Last edited by Steve69 (8/15/2014 3:04 PM)

I did not think about grinding the alternator to give pulley clearance. Might try that. 

I drove the car to Tennessee and back last year with that alternator and pulley, and the EFI pump screaming all the way.  Now I have the pump issue fixed.  The car has not given me any problems starting or running the ac or anything.  It just reads low voltage.  (AND I was experiencing that fuel pump flame-out on high speed acceleration, which could be voltage induced.  But it did not flame out in Tennessee).

First thought is just to leave it alone and see how it does, but the BASH THRASH is about to get in full swing so I need to get it right.
I am thinking about running a large gauge wire direct from alt to starter solenoid, in parallel with the existing wire to see if maybe the plug in the harness is actually limiting the current that gets through it.  It shows less than 1 ohm resistance through the plug, but that is with miniscule current only from the voltmeter itself.

I had some reward points at Autozone so I picked up a lifetime warranty alternator for free,even covering the core charge.  I am going to install it tomorrow and see if anything changes.

MustangSteve wrote:

Put new (free replacement for three years) Optima in the car.  Now it drives down the highway at about 12.5 volts and sits at 12 volts at idle.  According to Don's results as tested on his 66 Mustang, the voltage while running should be 14+.  Mine does not get there.


 

You are getting more voltage now only because the battery is in a better state of charge having just been replaced.  In a few days, you'll be back down in the 11s unless the problem is resolved.

The car should be charging at a minimum of 13.8 volts with a reasonably charged battery.  I think your alternator is weak.  Try unplugging the regulator, and jump the A and F terminals at the plug.  If the voltage jumps up, the alternator is good and there is a wiring or regulator problem.  If not, either the alternator or the heavy cable from the alternator is bad.

John

Unless you are going to install a 427 inch stereo and speakers you don't need no stinking 160 amp alternator.  But...if I read your post correctly you still have an alternator with the plug-in battery wire.  If that's the case you may want to scrap that or get one with a lug on the back of the case that take a 1/4" eyelet.  My alternator rebuilder rebuilt mine with the lug and now the only thing that plugs in is the voltage sensing and idiot light leads.  He told me those plug-in battery leads were nothing but trouble and had been know to get so hot...due to poor connection and high resistance....that they had been know to start fires.

Checking resistance on your high current connections is tricky as the very low voltage of the ohm meter will pass just fine but when you pour the juice to it it gets hot and the hotter it gets, the more resistance it creates.  Which is why dirty battery cable will: "Gee the lights come on just fine but it just goes "click" when I hit the starter."

Also...might just be that your old alternator needs new brushes.  If the exitation voltage is low  due to crappy brushes the output will not be up to snuff.  Changing the brushes is pretty easy.

BB


 

Instead of shimming your pulley out, why don't you shim the brackets that hold the alternator. That is how I got mine to move forwards. I did have to weld a dog leg for the lower mount to make it around the slightly larger 3G.

I had similar issues on a 78 E150 I used to have. A couple of things cropped up as it was not in great shape like I'm sure your mustang is. First my printed circuit on the back of my dash was kind of wonky. Where everything would not light up, or would intermittantly. 2nd thing I did was run a ground wire to the voltage regulator. Basically just put some eyelets on a 12 gauge wire and attached one end to a mounting bolt of the regulator and the other to the negative on the battery. Fixed all my issues, and yes when a vehicle is running it should have around 14- 14.4 volts, if its a diesel, high 13 volts is acceptable at idle.

KM wrote:

I would think you would want to figure your total load in amps DC, The voltage is not the main issue , If you use more amps than the altenator can supply then your battery makes it up , and as it drains down voltage will drop.

Since KM brought it up how do you measure dc amps?  Will my clamp on amp meter read DC amps?  I am very familiar with OHMS law and its application in AC? does it apply to dc in the same way?

Last edited by terry (8/16/2014 8:56 PM)

Mochaman wrote:

Instead of shimming your pulley out, why don't you shim the brackets that hold the alternator. That is how I got mine to move forwards. I did have to weld a dog leg for the lower mount to make it around the slightly larger 3G.

That would not cure the problem of the pulley hitting the front of the alternator.
 

You mentioned that alternator has worked for 20 years. That may be part of the problem now. ...(song time) The old alternator just ain't what she used to be, not what she used to be...

Alternators, degrade over time --brushes, windings, bearings, diodes. Before the latest engine install, the alternator didn't have to contend with the electrical component loads of the aditional items that have since been added. It may be the alternator was marginal, prior to the latest changes. Now that it's being taxed more, maybe it's just not up to par anymore.

The first dealings I ever had with the Ford 3G alternator was when I put one in my '90 Mustang GT around 1998/'99. More recently, I put one in my '69 F-100 because my stock 60 amp alternator was ailing and just not cutting it anymore.

I got the 130 amp 3G alternator, main charge lead, wiring harness and 175 amp mega fuse from the wrecking yard for around $25.00 bucks. I took the alternator to O'Reilly ' s and it tested good but, it had an obvious bearing problem.

I brought the alternator home, took it apart, bead blasted the housing, primed it and painted it with cast aluminum paint, put the new bearings on and put it all back together. When I went to swap the serpentine pulley for the V - groove pulley, from my truck's 60 amp alternator, the V - pulley bottomed out on the front of the alternator case. I took a very thin washer and placed it on the shaft between the case and the back of the pulley. This gave me the clearance I needed.

However, the (metric) nut (on my 3G) does not screw all the way down on the shaft threads but, I've been running it for a while now and the nut/pulley haven't come loose.

The only problem I had, at first, was the (new) belt slipping when first starting the truck up from the added resistance of the higher amp alternator. It seems to be under control now that the belt is 'broken in' but, in the event the squealing comes back, I picked up a double - groove pulley to swap in place of the single - groove pulley, where two belts can be put on it.

Narrowing down the possibilities...
Today I made a heavy duty 10 ga wire with soldered end connectors and bolted one end to the alternator and the other to the battery.  Basically it just parallels the large wire from the alternator going to the same place (the one with the suspect connector in the middle of the wire).

Made no difference.  That tells me the suspect plug is no longer suspect.

Even though the alternator was tested and PASSED at OReillys (no quantitative data, just pass or fail) I am going to go ahead and install the new alternator with the small pulley if it will work with my belt.  If it won't then the hipo pulley goes back on.

When I said it had been this way for 20 years, I meant the configuration of alternator and hipo pulley had been on there, not the same alternator.  This one is a polished one from ebay.  It says 100 amps now that I looked up the purchase.  The alternator was brand new about 3 years ago.

terry wrote:

KM wrote:

I would think you would want to figure your total load in amps DC, The voltage is not the main issue , If you use more amps than the altenator can supply then your battery makes it up , and as it drains down voltage will drop.

Since KM brought it up how do you measure dc amps?  Will my clamp on amp meter read DC amps?  I am very familiar with OHMS law and its application in AC? does it apply to dc in the same way?

Terry, Ohms law was written for D.C., A regular clamp on will not read DC amperage, but you can buy them that will read both, or if you have a fluke 87 they have clamp attachments that plug in that will work on both AC and DC.