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Fluctuating/inconsistent voltage


a2thy

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Greetings fellow RBV enthusiasts,
I come to you with a perplexing problem related to my truck's electrical system. A couple months ago my truck left me stranded with a dead alternator. I replaced it with a remanufactured one and all seemed well. Shortly thereafter the lights on my dash, along with my parking lights began intermittently dimming and brightening. This fluctuating of the lights is consistent with the readings of my on-dash voltage meter. The needle bounces up and down quite a bit, indicating that something is not normal. My first instinct is to blame the new alternator and/or voltage regulator (as they are both one unit), but I was wondering if this could be caused by something else. Let me know what you guys think I should do. Vehicle is a '97 Mazda B2300 2.3l 2wd 5spd manual, manual everything.

Thanks,
Austin
 
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Rock Auto 5% Discount Code: F9A1A579ACFAD1: October 1st, 2021

RonD

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It would most likely be the new alternator.

But I would check some voltages first.
Key off
Set voltage meter to DC Volts, 20vDC if available
Battery voltage should be 12.3 to 12.7volts

With Black probe on a Ground, put Red probe on Alternators B+ terminal, the big terminal on the back with the nut and large wire.
Should read same as battery's voltage, it is a direct connection to battery via a large fuse, no voltage = blown fuse.

Remove the 3 wire connector on the alternator.
You should see a light Green/red stripe wire, that's the wire from the Battery Light bulb and Volt Meter, this is also the ON/OFF switch for the alternator
Turn key on
That wire should now have Battery voltage

Also test Yellow/white stripe wire, that should also show battery voltage, there is a 15amp fuse in Power Box for this wire, it should be labelled ALT.
Turn key off

replace connector and start engine
test battery voltage again, should be 13.5 to 14.8volts
If below 13.5volts then alternator is not working correctly
 

a2thy

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Awesome. I'll be doing this as soon as I manage to find my voltage meter. Thank you.
 

a2thy

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So I just checked everything RonD suggested I check. Please keep in mind the outside air temperature was 13 degrees Fahrenheit and the truck hadn't been started in over 24 hours prior to this. Here's what I found:
Initial battery voltage: between 12.10v and 12.16v
Ground to alternator's red B+ terminal: 12.3v
Alternator's 3 wire connector with key in the "on" position, but not running:
-ground to green/white striped wire: 11.52v to 11.56v
-ground to yellow/white striped wire: 11.70v
Engine running, battery voltage: 15.35v to 15.40v
Engine not running battery voltage: 13.35v

I don't know what to make of all this. What do you guys think?
 

RonD

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Battery is a little low after sitting by 12degF will do that :)

The other voltage are OK except for after startup.

Over 15volt is not correct, should top out at 14.9v.
But could just be the meter.
14.5v is usual, and just after starting, then it should drop down to around 13.6v after a few minutes, over 14v "cooks" the battery if it is long term.
You need to measure battery a few minutes after shut down it should drop to around 12.5v
 

a2thy

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Ok, thanks. I'll try that. As far as the excessive voltage while running, the voltage gauge on the dash seems to coincide with my handheld meter, indicating that it may, in fact, be pushing that many volts. I'll measure it again as you specified, just to be sure.
 

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It should have close to 15v just after starting, but that needs to drop off in a few minutes after battery is recharged.
Maintenance voltage should be 1 to 1.2 volts above "at rest" battery voltage, that keeps battery charged but doesn't "cook it".

At rest voltage is tested after 4 or 5 hours(minimum) of sitting.
 

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15.4V is completely normal immediately after startup in 13°F temps. The alternator voltage is temperature compensated due to the chemistry of lead-acid batteries requiring more charge voltage when cold. As it warms up, the voltage will drop.

If it outputted 15.4V on a 80° day however, then that would be bad.


As for the fluctuations, do they occur more prominently at low RPM or right as you rev up the engine slightly from idle? (and also does it spike right as you shut off a heavy load such as the headlamps?) If so, I would agree the alternator is to blame (more specifically the voltage regulator is lagging in it's response time). I dealt with this on a replacement alternator for mine. Assuming this was a remanufactured alt you bought, I would suggest exchanging it for another one, maybe of another brand if possible. Or you could also swap out the VR itself for a genuine Motorcraft one (what I did to fix mine, since I had one on hand here). The no-name VRs in some remanufactured alts out there are garbage (probably from China).
 

a2thy

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Four months later and I'm finally getting around to fixing this. It's usually between 40 and 90 degrees this time of year, but I haven't tested the voltage recently. Yes, it does fluctuate more prominently at low RPMs, right after revving, right after switching off accessories, etc. The voltage regulator from my new/remanufactured alternator is still the primary suspect, and I will probably examine it further if the problem reoccurs.

I just had my mechanic complete a much-needed exhaust leak repair. Oddly enough, the voltage has seemed to remain consistent since then, though the recent functionality could be related to warmer temperatures instead. Could the recent adequate backpressure have fixed this? My mechanic told me to check the idle air control valve if the voltage/idling problem comes back.

Perhaps unrelated, but my truck just fried a wire connection in the harness for the headlight switch. It also did this about a year ago, so I'm about to replace the headlight switch for the second time.
 

Earl43P

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I suggest that you clean up all the grounds.

They are located:
Radiator Support, driver side of the radiator.
Left and Right Inner Fenders (3 total)
Head to Windshield Wiper motor mount bolt/firewall
B- cable should go Framerail THEN to the Passenger side of the block. Typical DIY replacement skips the framerail. In that case, run two new ones: one from Bat- to framerail and from that same bolt, another straight to the block.

A poor ground could certainly have caused BOTH of these problems, although the headlamp switch overheat/melt is Ford common.

There are other grounds, but these are the ones you should clean up for your problems.
 

a2thy

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I checked all the grounds you mentioned and they seemed to be in good shape, though I only found one ground on each inner fender and couldn't find any ground connected to the passenger side of the block. Following the negative cable from the battery, it connected to the left frame rail, continued underneath the oil pan, then terminated at the starter solenoid. Where on the block should this ground be located? and where exactly should the three inner fender grounds be located?
 

a2thy

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If the third inner fender ground is the one that connects to the horn on the front of the left inner fender, then I found it. I still don't know where the ground is on the passenger side of the block though.
 

a2thy

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So I did a little engine degreasing along with wire brushing and applying dielectric lubricant to all the grounding points I was able to access. The voltage continues to fluctuate. I have found no evidence whatsoever of a ground having ever been connected to any part of the engine block. I've been told it should be near or on the passenger side motor mount. If this is the case, should I just run a new ground directly from either the frame rail or battery post to any of the motor mount bolts on the block? If so, what gauge wire should be used?
 

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Im having the same issue with my ( Ford Ranger 1997 2.3 5 speed ). But I seem to have a little more of a problem. Heater blower has stopped working about 6 weeks . Thank god the weather has been fair. New resistor , blower motor works on direct 12v from battery , new heater controll switch s ( high med low , and heater vent def switch .
This came to my attention when I started working second shift on my way home with lights flickering along with the in side dome light as well .
I did find a ground wire down on drivers side kick panel . I pulled this and cleaned along with the others mention in posts before this.
Thanks all for sharing so much already . I need my blower as well as head lights to stop their blinking. :icon_thumby:
 

a2thy

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So I take it the cleaning of your ground(s) didn't quite fix the problems you're having?

I took a look at the driver side of my engine block with a borescope and found a grounding wire hidden behind my p/s pump and a/c compressor. It's securely attached to the driver side of the block and I have continuity between all the grounds listed previously and then some: valve cover, head, block, oil pan, intake manifold, both frame rails, both inner fenders, firewall, hood, etc.

One odd and possibly related finding was that in my power distribution box I found the #9 and #10 maxi fuses to be missing, as well as having no terminals for them to plug into. It's as though these slots weren't used for this particular model of the B2300, though my Chilton manual tells me otherwise. The #9 slot is supposed to be used for the ABS System Main Relay, the #10 slot is supposed to be used for the ABS System Pump Relay, my #24 (PCM) diode is fried but that seems less mysterious.

My local parts store didn't have any replacement diodes, so I wasn't able to change it out yet, but I'm guessing that that may make troubleshooting this problem a little easier. Let me know what you guys think about all this, particularly the missing connections for the #9 and #10 maxi fuses in the power distribution box.
 


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