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Old 01-06-2016
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Voltmeter going crazy

Hi, i am new to this Forum and i would like to see if you guys can help me out.

I have a 1994 2.3 with manual transmission, the voltmeter is going from about 13-17 volts like crazy, when i rev the engine at 3000 RPS aprox the voltmeter will stay at 14 volts aprox. but otherwise it will fluctuate like i said before, sometimes a little more, it has a new battery, it starts and cranks with no problem but i am afraid that at some moment a high peak voltage could cause some electrical damage.

could it be the alternator?? or just the regulator???

i was told maybe could have some problem with a ground conection, where should i look for that??

any info will be appreciated, thanks!!
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Old 01-06-2016
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If you're relying on the dash gauge, I'd recommend verifying with a portable volt meter first.
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Old 01-06-2016
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Quote:
Originally Posted by Rev View Post
If you're relying on the dash gauge, I'd recommend verifying with a portable volt meter first.
I forgot to write that is easy to tell the fluctiation in the dash illumination, also the reading lights and the head beams, but ill try to get a portable meter
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Old 01-06-2016
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Yes, check it with a volt meter with engine at idle, then 2,000rpm, then 3,000rpm
Voltage should stay between 13 and 15volts

Voltage regulator is in the alternator, and you description does read like it is going out.

The voltage regulator sends 5 to 9 volts to the rotor of the alternator.
The case of the alternator has 3 "field coils", as the rotor spins these field coils generate AC(alternating current) voltage, hence the word "alternator", each field coil has 2 Diodes, this converts the AC voltage to DC voltage, battery and truck electrics use DC voltage.
Because the engine is spinning/powering the rotor, 5 volts in will get 13volts out, 9 volts in will get 17 volts out.

The voltage regulators job is keep voltage between 13.5 to 14.5volts, regardless of RPM or load, i.e. lights on, heater fan on high, ect....

Your voltage jumping around could just be a bad gauge, which is why you need the volt meter test.
But it could also be failing voltage regulator or failing diode, if diode starts to fail AC voltage can leak into the DC side and cause voltage spikes.
But in any case voltage spikes above 15volts can damage electrics, and shorten battery life, battery "boils" off fluid.
So the sooner the better in check this out.


Could be a loose wire, but it should get worst with higher RPM and vibration, and you said it got better
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Old 01-07-2016
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Thanks guys!! i decided to buy the regulator since it costs the equivalent to 7 dollars, i replaced it and it solved the issue, now i just have to change the brushes they look like they are close to the end of its life.

thanks!!
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Old 01-07-2016
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Good work

Thanks for the update.
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Old 01-08-2016
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And I was just going to say replace the regulator... Lol !

While you are rebuilding the alternator and you are handy with this stuff... consider replacing the grounding wires, minimum the battery to the frame but consider do as many as possible.
I like to add a ground wire from the battery to one of the starter bolts, this helps the starter and battery when starting, there is also the alternator to frame, battery to body, engine to frame etc. !

Just thinking out loud, there is also something the site calls the big three, search for it.
I had a 95 2.3, manual, great truck, 24 mpg/avg., I added grounds to the frame, alternator, engine and starter, I believe the truck ran smoother, something to do with ground path being better.

Good Luck,
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Old 01-08-2016
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It is not uncommon to lose 1 "field coil" as alternator gets older, this will lower maximum output but at engine RPMs above 1,500 it will generate enough power to charge battery and run truck electrics.

Sign of this failed or failing field coil is head lights dimming at warm engine idle, 600-750rpms
No, that is NOT normal, lol, unless you have added a lot of extra lights or a big subwoofer

No manufacture specs an alternator that doesn't produce at least 13.5volts at idle, 600rpm
Head lights dimming means system voltage is dropping at idle which is the sign of a problem, usual a coil or its diodes have failed.

It can also mean regulator is sending out too much voltage at higher RPMs, so the dimming head lights are a return to "normal" voltage.
After initial recharge of battery after starting engine, 14.5-15volts, voltage at battery should be at 13.5-14volts when you increase RPMs voltage should go up then drop back down within that range as voltage regulator lowers voltage to specified range
Turning on lights and other electrics should see a drop in voltage then it should come back up as voltage regulator increases voltage to specified range

Last edited by RonD; 01-08-2016 at 12:35 PM.
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