3FE voltage issues

[tacoma2002]

I've tried searching but I cant nail down a definite answer to my problem. I'd like to get some opinions before I just start replacing parts...

While driving at night my voltage will drop to a little over halfway (on voltmeter) then pick back up to the mark before the uppermost mark. This happens randomly and more so some days than others. I really notice it in the headlights when the voltage drops because the headlights pulse.

It does this during the day as well but its not noticeable and it does not do it nearly as frequent.

Alternator shot?

TIA.

 

[Malleus]

Voltage regulator would be my first suspect.

 

[Pitch]

Alternator, most likely. IIRC, the voltage regulator is a non, to barely serviceable part of a new/rebuilt alternator.

However, I find the 3FE stock alternator barely adequate, even when new. Winter time, with heaters blowing on high, sees my headlights dim substantially when I am at a stop light. (Alternator is a 2yo Toyota-sourced reman. unit)

 

[tacoma2002]

That's where my mind went...

What's the "regular" voltage? The high mark or the middle mark?

Is the alternator internally regulated?

I know the alternator has two variations 80A and 90A. I believe mine is the 90A variation but I have not confirmed. Just trying to go by memory.

 

[tacoma2002]

Alternator, most likely. IIRC, the voltage regulator is a non, to barely serviceable part of a new/rebuilt alternator.

However, I find the 3FE stock alternator barely adequate, even when new. Winter time, with heaters blowing on high, sees my headlights dim substantially when I am at a stop light. (Alternator is a 2yo Toyota-sourced reman. unit)

I have installed a GM 120A alternator on my Tacoma. I was wondering if there was a similar alternative to the 80S. I have read about "hopped up" alternators but they seem to be out of my price range. Anything under $200 I can justify...anything more I cannot.

I'll be looking at doing a Dual battery setup in the next several months so the small amperage output might not be an issue then.

I'm green in the 80 world so I appreciate all the guidance!

 

[mct75]

My 92 dims at red lights and the blowers definitely slow down. It has a denso-remanufactured alternator of unknown age. Does the FSM spec an acceptable voltage at idle?

 

[jonheld]

The alternator is only part of the charging system. The condition of the battery, cables, and connectors are all in play here. If the system is in good shape, the stock 80 amp unit is more than sufficient.

 

[ppc]

Have you checked the simple stuff like belt tension and connections?

 

[tacoma2002]

I have. Connections seem fine and belt is tight.

I need to unplug it and inspect the pigtail though.

 

[jonheld]

Connections seem fine and belt is tight.

When you say things like, "the connections seem fine" it makes me wonder if your eyes are a multimeter. Your eyes cannot measure voltage drop. Your eyes cannot tell if the battery is accepting and holding charge correctly.
Batteries typically have a 5 year lifespan depending on climate and usage. The very first thing I would do is have your battery tested. IME they are almost always the weak link in the system.

On a good system, the voltage across the battery terminals should be about 14.4 or so after starting and at idle. This will at least tell you that the alternator is charging. However a lower reading could be indicative of a failed cell in the battery or poor alternator output or bad cabling. A higher reading would indicate a failed voltage regulator which in turn could damage a good battery.

A charging system is a "system" not just a bunch of parts. They all interact with each other like every other "system"on the vehicle.

 

[tacoma2002]

Brand new optima Red.

Cables don't show signs or wear or over heating.

Plug is not melted or corroded.

I will check output with MM today.

 

[tacoma2002]

Voltage is fluctuating between 12-17V. Replaced the alternator and issue is resolved. I can only believe that the voltage regulator was bad inside the unit.

 

[jonheld]

Voltage is fluctuating between 12-17V. Replaced the alternator and issue is resolved. I can only believe that the voltage regulator was bad inside the unit.

I would have your battery tested to be certain the overvoltage did not cause damage.

 

[stridertexas]

My 62series 3fe is having big voltage drops on the dash gauge.

This pic shows my voltage with brake lights on (pedal pressed), brights on, Hester going, and blinker going.

There are no additional accessories wired on my rig.

Should the voltage dip be that much with such typical usage? Makes me question adding any more load/draw to the system.

This is all at idle too btw, which I would think would be at minimum what one would set up for...

Sorry if this is a newb question. I’m learning as I go. I have a multimeter. How can I tell if the battery, alternator or voltage regulator are wearing out?

 

[CJF]

Holy moly!

That's down around roughly 10v according to your gauge?

Never seen one anywhere near that low except during startup while cranking.

Start by checking voltage across the battery with the rig off, and then with the rig on but all accessories off.

 

[Marine7]

That’s not too bad. Blinkers draw big time juice. Your at 600rpm, and everything on. I’m guessing you stab the go pedal, and the charge needle will jump up to the halfway mark (actually a bit over half) which is right on the $$$..... Another vote from me pointing to battery is shot. And I’m not trying to be a ass, but stay away from Optima....new ones are garbage compared to the older ones, Can’t go wrong with Interstste or Wally World batteries.