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Alternator Gurus Needed

75Bronc

Sr. Member
Joined
Feb 5, 2008
Messages
425
I just put a replacement 130 amp 3G alternator in my bronco. The part store warrantied my old one even though it didn't end up being what was wrong. I had just lost 12V to my ignition. Anyways here is the issue.

The day I installed the new alternator I drove 120 miles and through Phoenix. There was a wreck on the 10 and I was stopped in traffic for 45 minutes. During this time my engine temps rose a little but not bad, 205 ish. My alternator however stopped charging. When I got it back up to highway speeds, it started charging intermittent for a little while. And then pretty soon it was charging good again. When I got to my destination not far from the wreck, it was charging perfect. I checked it out and everything seemed right. I drove it home 120 miles and have put on a couple hundred more miles since. No hiccups in charging. My alternator is on F250 front dress and it sits up high on passenger side with no air flow, no alternator fan and a radiator hose right in front of it.

Could my alternator have over heated and started cooling again when it got air flow? What else could have caused this? Should I be concerned about my alternator?

Also, my old alternator charged around 14.7 and this new alternator charges around 14.2-14.3? Why the .5 difference? Is this a concern?

Thanks!
 

RODRIG3911

Contributor
Sr. Member
Joined
Jul 9, 2007
Messages
968
Loc.
Tucson
Mine was doing that same thing. What I found was the 3G alternator that I installed only had one single V belt pulley and since it was a higher amperage alternator, it was requiring more effort to turn it which was causing my belt to slip and creating heat that was making my alternator intermittent from over heating..... Anyways, I installed a dual grove v belt pulley and it's working fantastic. You might have the issue I did
 

spap

Contributor
Bronco Guru
Joined
Jan 2, 2010
Messages
2,455
Can’t help with much of it but the 3g alts have an internal fan, to keep them cool. But sitting in Az can always raise temps.
How are the grounds, do you run an external ground wire.
 
OP
OP
75Bronc

75Bronc

Sr. Member
Joined
Feb 5, 2008
Messages
425
Thanks for the input, my front dress is serpentine. I thought it could be belt slipping, but figure it would be tough with a serpentine, especially with a new tight belt.

Thanks for the info on internal fan, didn't know that. I think I have a good ground. The alternator is grounded through the engine block, and I have a ground going from the block to the negative on my battery.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,275
Is the engine block painted though? And were the threaded bolt holes a little rusty? If yest to either of those, you might still be getting a ground, but it might not be as good as it could be.

However, the .2v difference between them could be simple variations in the voltage regulators.
It could also be a slight difference in conductivity on the Yellow wire.
Speaking of which... Is your Yellow wire connected directly to the output post on the alternator? Or is it run up the harness closer to the battery to get it's signal?

Either way though, that 14.2 is sufficient. It's maybe not quite as good as having that extra .2 to .5 volts perhaps, but it's more than enough to keep the battery charged and the system working to snuff.
A good test would be to run all the accessories up as high as you can the next time you're messing with it to see if the voltage goes down and stays down.
Turn the heater blower on high, hazards on, high-beams and such, and watch the voltage reading.
If it goes down momentarily then comes back up, you're fine. If it goes down and stays down for more than a few minutes, the alternator is weak.
At this point you're testing at idle, but you can rev the engine up a bit to see if things start to come back up. But to my way of thinking, up to a point that's still a weak alternator, as the 3G is supposed to be able to put out more than 70a at idle. Which is more than enough for the common loads on a Bronco. Even at idle.

Back to the low reading at idle in traffic, how long did it stay there? Maybe at higher temps the alternator was not able to put out quite as much. But the fact that it came back up does seem to indicate it's still capable of working.

Keep an eye on it, but don't sweat it at this point.

Good luck.

Paul
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
3 g alternator is really ground sensitive. There are threaded holes on the case so to be safe run a good seperate ground to the ground cable meeting at the block. Dont trust what seems to a good ground through the mounting brackets.
 

Steve83

Bronco Guru
Joined
Jul 16, 2003
Messages
8,976
Loc.
Memphis, TN, USA, Earth, Milky Way
My alternator however stopped charging.
Define "stopped charging". Does the truck have a voltmeter, an original ammeter, neither, or something else?
...it started charging intermittent for a little while. And then pretty soon it was charging good again.
How exactly do you know?
I checked it out...
How exactly? What exactly did you check, and what reading did you get on each thing? Where were the meter probes each time?
My alternator is on F250 front dress...
What exactly does that mean? Post pics.
...no air flow...
Air flows everywhere when you're moving at highway speeds.
...no alternator fan...
3Gs have 2 fans; one at each end of the rotor.
...a radiator hose right in front of it.
That doesn't affect anything.
Could my alternator have over heated and started cooling again when it got air flow?
No. If it had overheated, it would have changed colors, and it would stink, and it probably would have burned its fusible link or fuse (depending on what you have - post pics).
What else could have caused this?
Belt slip, but it depends on exactly what you mean by "stopped charging".
...this new alternator charges around 14.2-14.3? Why the .5 difference? Is this a concern?
Yes. Have you ever done what these pics show?


(phone app link)



(phone app link)



(phone app link)



(phone app link)


Clean the OTHER end of each heavy cable, too:


(phone app link)


What do the battery terminals look like?


(phone app link)
 
OP
OP
75Bronc

75Bronc

Sr. Member
Joined
Feb 5, 2008
Messages
425
Steve83,

I have FiTech and the handheld controller mounts on my dash with a live Voltmeter. The alternator went from 14.2 down to 12.2 volts when it "stopped charging".

When it started charging intermittent, it was bouncing between 12.2 and 14.2.

I checked the wiring was not fried, I had a voltmeter in my bronco so I test the terminals and everything seemed right. The Charge terminal and yellow wire had 14.4 volts while running. And the green/red wire had 12V with ignition switch on. It did not seem like belt was slipping at all.

"F250 front dress", the 351W came from a 1990 F250, I have the serpentine front dress from that truck.

I don't know if it changed colors, but it did smell a little stinky in traffic, like melted plastic. I don't know if it was the alternator or something else, but I did smell something getting hot, by the time I got to my destination it was gone.

I have not thoroughly cleaned and put electric grease on my connections and grounding surfaces. I will check ground resistance today.
 

Steve83

Bronco Guru
Joined
Jul 16, 2003
Messages
8,976
Loc.
Memphis, TN, USA, Earth, Milky Way
I have FiTech and the handheld controller mounts on my dash with a live Voltmeter.
Unless you use a meter connected DIRECTLY to the battery terminals, you're not actually measuring battery (charging) voltage. You're measuring voltage right outside the FITech box, which might be lower than battery (B+) due to resistance between the battery & FITech, or it might be higher than B+ (only while the engine is running) due to resistance between the alt. & batt. Bouncing voltage suggests a broken connection SOMEWHERE... The point being: you have to check ALL the connections along the path between the battery, alternator (if the engine was running during the symptom), & whatever meter is showing the problem (the FITech, in your case).
It did not seem like belt was slipping at all.
Based on what observation? Lack of squeal? The belt can slip silently if there's contamination on the pulleys.
...351W came from a 1990 F250, I have the serpentine front dress from that truck.
Then it would be clearer to say that it has a '90 5.8L serpentine system. Just saying "F250" doesn't indicate year, engine, or what you're talking about.
...it did smell a little stinky in traffic, like melted plastic.
This is what I took out of my Bronco a few months ago:


(phone app link)


Just before it failed completely, voltage was unsteady. When it failed, there was a strong odor of burning plastic & varnish.
 
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