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Voltage Drops During Idle


wildbill23c

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I'm thinking the alternator in my 88 Bronco 2 is failing. At idle under load, lights on and heater blower motor on the voltage drops to 12 volts, sometimes less. Lights dim, etc.

Question is how do I know which alternator it has? Is there an OEM amp size that they come with? I plan on adding a few lights and a couple Ham radios here soon so some extra juice would be nice but not really into wanting to do a huge modification for a alternator that doesn't belong.

So I'm wondering if there's an alternative alternator that will fit without having to modify anything. Looks like the current alternator has an internal regulator. Could I get an alternator and do an external regulator? Would that give me more amperage options and more alternator options? Looks like right now a direct replacement alternator is $100+ and only like 60 amps.

Battery tests good. Could the voltage regulator just be bad?
 


Slammin Sam

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O Reilly lists an 80 amp alternator for $99.99, their Part # R111700B The pulley is for the serpentine belt, but they will install your old v-belt pulley. I replaced the 60 amp on my 89 with one. I know I say some 100 plus amp units on eBay when I was replacing mine. IIRC, they get pretty expensive.
 
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4x4junkie

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A 95-amp 3G alternator from a 1995 4.9L I6 (E-150 or F-150) should fit right onto your stock mounts (it did on my '90 2.9L anyway). Only thing is you will need to modify your wiring slightly.

IIRC... I lopped off the rectangle 3-pin B+ output plug and then installed a heavy-duty ring terminal onto the two large wires (both wires can go into one terminal), this attaches to the output connection on the back of the new alt. The center wht/blk wire coming from the volt regulator plug then has to connect to the single pin terminal that is next to the volt reg socket on the new alternator.

Sounds more complicated than it is, it was a very simple modification.
Charging performance at idle was much improved over the stock 2G 60-amp alt (no voltage sag even with the lights on and the blower fan on max).

The '95 amp 3G alt also comes with a serpentine pulley so you will need to swap your stock pulley onto it.

Hope that helps
 

wildbill23c

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The current alternator has an internal regulator so I'm kind of stuck with that problem which means ridiculous priced alternator replacement.

Not going to worry about it until this alternator dies completely. So I can have time to hopefully find a replacement that doesn't require me hacking the stock wiring.
 

4x4junkie

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:rolleyes:

It would be EXACTLY how the stock wiring is on vehicles designed for the 3G alt. In fact, if you really wanted to make it look "OEM", you can get the little single connector at a junkyard and then install it's wire into your VR plug by swapping out the pin (I just spliced it in on mine).

The 3G alt is 10 worlds ahead of what the 2G (junk) alt is.
 

RonD

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On ebay stock 80amp is $70: http://www.ebay.com/itm/ALTERNATOR-FORD-2-9-BRONCO-II-87-88-89-90-4-9-7-5-F-SERIES-PICKUP-90-91-92-93-/140740550812?fits=Make:Ford|Model:Bronco+II&hash=item20c4ca609c:g:jlkAAOSwnLdWsmef&vxp=mtr

And that is fine.

Your current alternator has 3 fields that make AC voltage, 1 of them has failed.
This doesn't reduce power by 1/3 however, because voltage regulator cranks up the rotor voltage to compensate, BUT...............at idle you would see the problem as dimming head lights from lower voltage because even at max rotor voltage the low alternator RPM just can't support vehicle AMP draw with only 2 working fields.

Normally an alternator will have about 60% of its amps at idle, engine RPMs 700
So your B2 needs less than 50amps with lights and fan on high.

And it is currently running at 30amps, maybe, at idle, so it does work, lol, just not well at idle.

Adding radios and extra lights shouldn't effect working stock alternator.
Yes, getting a 100amp or 130amp is better, can't have too much power, but it is not always necessary
 

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I had similar problems, I took it off and brought it to the bench to have a look. Upon opening it up I found one of the brushes not sitting right and a ton of corrosion inside. All the contacts and the windings were green. I cleaned it all up with terminal cleaner and used a set of brushes out of one that was sitting around d in my shop. Reassembled it and put it back in the truck. Now my truck charges consistently at 14 volts, it has been 2 years now and still charging at 14.



Sent from my XT1064 using Tapatalk
 

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There is a tech article HERE about alternators that has a chart showing what came in which RBV's and what can swap in. I'll be testing the info tomorrow. I just got a 130amp alternator from the junk yard that I hope to use as a replacement for my 95amp. The 130amp looks like a brand new Motorcraft alternator - all nice and clean and shiny with factory sticker on it. I found it in a '95 Ranger with 4.0L. I'm putting it in a '93 with 3.0L. I also grabbed the wiring harness with the proper fusible link for the bigger alternator.
 

wildbill23c

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Thanks everyone. This is definitely on my priority list. I don't like messing with wiring too much if I don't have to. So, I may just stay close to stock as I can, but if an 80amp alternator is stock size, I think someone just threw a 65amp in because the number on the current alternator shows it as a 65amp when I put the number into autozone or oreilly.

The link that RonD posted on ebay looks like all I need to do is swap pulleys, not that big of a deal I don't think.

Weather is starting to warm up so I'll be tackling these things here very soon. I'm worried that if it goes too long running 14+ volts all the time while driving that its going to damage the battery and other components...wonder if that alternator is causing the terrible squealing noise from my radio on FM stations too?
 

4x4junkie

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I'm worried that if it goes too long running 14+ volts all the time while driving that its going to damage the battery and other components...
That I wouldn't worry about. 14.1 - 14.4 volts is completely normal on an average temperature day with the engine warm (the voltage can actually hit 15V or a tad above on cold days and/or when you first start the (cold) engine, but it should drop down into the 14s as it warms up)

This does not harm the battery at all (in fact, too little voltage is more likely to shorten the life of your battery)

As for the squealing noise in your radio, that could still be caused by the alt having bad field or rectifier (this creates a bad ripple voltage in the output), but not because the voltage is in the 14s.
 

wildbill23c

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That I wouldn't worry about. 14.1 - 14.4 volts is completely normal on an average temperature day with the engine warm (the voltage can actually hit 15V or a tad above on cold days and/or when you first start the (cold) engine, but it should drop down into the 14s as it warms up)

This does not harm the battery at all (in fact, too little voltage is more likely to shorten the life of your battery)

As for the squealing noise in your radio, that could still be caused by the alt having bad field or rectifier (this creates a bad ripple voltage in the output), but not because the voltage is in the 14s.
Thank you for the information. I purchased an alternator at pick a part...of course its no good...so the alternator in my bronco 2 at least functions...not completely but at least keeps it going. Found an alternator on ebay that's an 80amp just has the wrong pulley on it for $70, going to order one and get the pulley swapped out...looks like it may be a pain in the ass to change the pulley...maybe not with an impact gun?

The alternator in the bronco 2 I had tested and it sort of passed pointing towards that one field that isn't working. So once I get the alternator replaced I should be good to go for a while LOL.
 

4x4junkie

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Yeah, getting the nut off to change pulleys is piece of cake with an impact.
 

wildbill23c

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wildbill23c

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I ordered an 80amp alternator from ebay a while back, finally got around to installing it this evening. Works great no more dim lights. Didn't cure my radio squealing but wasn't really expecting it to either so a new radio will be in the future.

Alternator I ordered had a serpentine pulley on it, took the impact and swapped pulleys. The pain in the a** part was getting to the bolt on the back side of the alternator on the bottom...other than that it was extremely simple as it should be. Also, after the alternator replacement I notice it idles smoother, wondering if the bad alternator was causing some voltage problems to keep the thing from idling properly.
 

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Good work

yes, lower coil voltage = lower spark voltage

radio noise is fairly easy to identify
Does noise change with engine RPM?
If yes then alternator, coil or spark plug wires are the issue.

Any electric motor like blower fan or fuel pump can cause radio noise

Antenna's base must be properly grounded to body, and so to the Radio chassis, or the antenna is just doing what is suppose to do, pick up RF waves, but thru the BODY of the truck.
So this is the very first thing to check.

Cold engine
Loosen fan belt and take it off alternator
Start engine, see if radio noise is gone, if not then alternator is not the source.
If noise is gone then you need to add suppressor to alternator

For the rest read here: https://www.howacarworks.com/accessories/identifying-and-suppressing-radio-interference
 

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