Low Voltage, 03 4.0 - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 10-24-2009
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Low Voltage, 03 4.0

This is on Kevoo's truck, not mine.

It's a 2003 4.0 auto, essentially no electrical mods.

Everything was fine, and randomly while driving it almost stalled and showed a low voltage condition.

We had the alt checked, it's within limits

The battery should be fine, it cranks up with full power

I used a jumper from the alt to battery...and it made it hard to start and run a little rough at idle, so I'm not sure what that meants...

We cleaned the battery terminals...that did no difference


When you rev the truck up, it will go up to regular voltage, when it is idleing with the lights on and ac, it is all the way down (running off the battery) and everything dims...engine runs a little rough.

Any ideas???

I am almost thinking it's the battery...event though it starts fine, maybe something is still wrong with it?
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Old 10-24-2009
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to the top
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Old 10-24-2009
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my guess would be voltage regulator
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Old 10-25-2009
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to the top again...

the stock alt was tested and voltage reg was within normal limits
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Old 10-25-2009
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I'm thinking that the best way to fix it is find a really deep lake and go really fast... ?
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Old 10-26-2009
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Quote:
Originally Posted by jrpro130 View Post
to the top again...

the stock alt was tested and voltage reg was within normal limits
i had a similar issue with a 2000 Grand Am. the voltage regulator was failing at a certain RPM level. I'd take it in to get checked and it checked out fine. Problem is, when they check the alternator, they only check it at a certain RPM, not a whole range.

Throw a volt meter on the battery and watch it. I think the magic number it shouldn't fall under is 13.8v with the engine running and alternator running properly.
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Old 10-30-2009
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It will charge when rev'ved up...

He already put a new alt on it and it did the SAME exact thing.

We tried using a jumper from the alt to battery and it made no difference, made it harder to start actually
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Old 10-30-2009
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I'm with ccernst, put a meter on the battery. If it holds voltage with the truck idleing, the alternator is working like it should. If the voltage drops with A/C and lights on, then more than likely the regulator is bad. You should get a momentary drop in voltage across the meter, but the regulator should adjust the voltage output up to compensate. If voltage does not come back up, then the regulator is bad.

This is also making the assumption that both the original and replacement alternator are functioning properly.
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Old 11-06-2009
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It still had low volts with a new alt...so that would mean it is NOT the voltage regulator?
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Old 11-06-2009
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Your voltage regulator is bad. Don't you just love buying the expensive part that wasn't bad, when the cheapo part is the culprit. Don't worry, you're not alone doing that....trust me!
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Old 11-06-2009
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I haven't messed with the alternator yet on the Ranger, but aren't voltage regulators built into the alternator? It was on the Grand Am's alternator. So if he replaced the alternator, he would have replaced the voltage regulator as well.
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Old 11-06-2009
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Quote:
Originally Posted by ccernst View Post
I haven't messed with the alternator yet on the Ranger, but aren't voltage regulators built into the alternator? It was on the Grand Am's alternator. So if he replaced the alternator, he would have replaced the voltage regulator as well.
Yes, the voltage regulator is a solid state unit built into the alternator. It has to be bad. Did he get a remanufactured or rebuilt one?
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Old 11-08-2009
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He bought a reman from Autozone. It tested fine on the machine...as well as the stocker.

There is a specific test for the voltage regulator on the machine, and it tested within limits. The reman alternator was just a tad better than the stock.
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Old 11-08-2009
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like I said before, I had an alternator where it tested fine on their test machine, but that is only at a certain rpm level, not the range a vehicle will spin the shaft. what are the voltages it is outputting when idle?
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Old 11-08-2009
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Haven't got a DMM on it yet, looks to be less than 12v because it is running off the battery.

At about 2k rpms it jumps up to normal 13.5-14.4 volts, it is in the normal range.

The whole thing I am saying is that the new alt didn't do anything...ran the exact same.

With a jumper from alt to battery the truck wanted to die...

I am going to try to run it without the battery hooked up and see what the volts are...seems like the battery may be drawing too much voltage
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Old 11-08-2009
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it may not run without the battery but you may have just said the problem, theres a wire that is hot to energize the alternator, not remembering what it is called right now so sorry for the shady discription

long story short, if this wire is not hot, when the alternator spins faster than 2k rpm it will energize itself...ill get back to you on this when it isnt bedtime
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Old 11-09-2009
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Disconnecting the battery can fry the voltage regulator. The battery balances the output of the alt.

Sounds to me its a wiring issue. You need power in to the alt to get power out. Check the connectors on the alt for damage or corrosion. Also look at the ground on the battery and from the engine to chassis. (usually at the wiper motor)

Is the battery light on?
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  #18  
Old 11-10-2009
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Battery light is not on. I have checked every connector and everything I possibly know of.

I had these same probs and it was my ALT...replaced it and the battery and was fine until I sold it.

I just can't fig out kevooo's problem
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Old 11-10-2009
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I don't know if it helps, but I just replaced my starter cause it was drawing every amp my battery could put out...resulted in a junked battery.

Didn't realize until I turned on my hella 500 lights and my truck would stall on the highway cause I was borderline "not enough juice". 10v isn't enough to run a truck. Found out first hand.
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  #20  
Old 11-13-2009
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i would be checking for loose ground wires, like the body to frame, engine to frame. Also, does it have a fusable link?
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