Voltage Drops Out.....

Ol'Blue

Ol'Blue

New member
So on the way home tonight my head lights started to fade out. The head lights start to dim a bit but nothing to crazy but I noticed it. So I tested it at the local O'R. I know rule number one. Don't trust O'R. Any how, I was a bit on the low side on the Alt. So after a beer and about 30 minutes new Alt was put in the truck. Also new head lamp bulbs too.

Anyhow, I get it all back together and the same issue on my test drive. Well like a retard I forgot about my scan guage in the truck. Derrrrrr......

When my foot is in the gas pedal the numbers are at 14.3-14.7

As soon as I get my foot out of it the Volts just drop out, I was hitting 11.4 when everything was on while the truck is in Drive.

What are some thoughts. And yes the Alt is in correct also.

Thanks guys

Blue
 
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What's the resting voltage of the battery sitting at? Usually dropping into the mid 11's means your battery is on the way out since that's well below a normal resting voltage.
 
Should be getting 14v at idle. If standing voltage of battery is over 12v I would suspect alt or cables.
 
Maybe a loose connection, bad cable, or ground. Seems like the ALT is trying to overcharge. I see 14.2 at initial start up, then as low as 13.4 but no lower.

Add any electronics lately?
 
Starting is at mid 13. Then will hold at 14.1 until I put it in drive and idle. The At is brand new. Put it in last night and it was still pulling this silly stuff. All the battery terminal connections are tight the cables are tite also. I'm going by Sears this morning and going to warranty out the battery
 
LittleCaesar said:
Maybe a loose connection, bad cable, or ground. Seems like the ALT is trying to overcharge. I see 14.2 at initial start up, then as low as 13.4 but no lower.

Add any electronics lately?
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Nope. All have been the same for some time. Even after new alt it did the same thing. I was watching the scan Guage and it fell out pretty quick when I put the system under a load. Only thing I didn't have on was the winch. Air locker were going and that's when it fell into the low 11's.
 
If the belt isn't slipping, you have a bad alternator. Even if it's brand new.

I'm guessing you got it at one of the discount auto parts stores, and they're selling straight up Chinese junk. I went through THREE on my RV in 5k miles, and it needs another one now, all from Auto Zone. I'm just giving up on the warranty and buying a good one when I change it this time.
 
Ol'Blue said:
Starting is at mid 13. Then will hold at 14.1 until I put it in drive and idle. The At is brand new. Put it in last night and it was still pulling this silly stuff. All the battery terminal connections are tight the cables are tite also. I'm going by Sears this morning and going to warranty out the battery
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Seen this million times. I would guess bad new alt. Like said above I literally seen people get bad alts out the box three times. OEM our high quality rebuild only. I would trust junk yard way before cheap auto part chain.
 
jeremyc74 said:
If the belt isn't slipping, you have a bad alternator. Even if it's brand new.



I'm guessing you got it at one of the discount auto parts stores, and they're selling straight up Chinese junk. I went through THREE on my RV in 5k miles, and it needs another one now, all from Auto Zone. I'm just giving up on the warranty and buying a good one when I change it this time.
Click to expand...


This^^ I replaced mine five times within 2 months because all they sell you is refurbished crap.
 
Guess where I got it from hip O'Reilly go figure right so I'll try this again when I get home tonight
 
I would second and third what has been stated already, bad alternator.

I say this because I had identical symptoms a few years back. Lights were randomly dimming. I ignored it for almost two weeks. Then on an awesome fall Friday night I was driving through the woods and all my electricals continued to slowly dim until I broke down. That's the only time the truck has left me stranded, and it was totally my own fault for ignoring it
 
JayRolla said:
Seen this million times. I would guess bad new alt. Like said above I literally seen people get bad alts out the box three times. OEM our high quality rebuild only. I would trust junk yard way before cheap auto part chain.
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This says it all... Guess we go back to the cheap ass Alt. Ugh!
 

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Did you ever replace the 12" battery negative to chassis ground cable with 4G?

Although it isn't the entire big three it makes a lot of the difference and only takes 5 mins.

BTW I had a similar experience to yours several years ago. I thought my alternator was bad but it was just my battery.

The only real difference finally came after I bought a new interstate heavy duty battery, started leaving a trickle charger in the dash (I don't drive it everyday) did the big three upgrade.

12.5 V voltage while sitting on your counter is pretty good. I don't quite understand how the mystery was solved.
 
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Remove the rear cover of your alternator and remove the brushes. Let us see the size of the brushes. It is either brushes or the diodes.

Take the brushes in your reman alternator and put it in your toyota alternator. Give it a try.

Never buy aftermarket alternators. I have the factory alternator in my toyota car and both my truck and car gives 13.8 V at idle (with AC/headlights and wipers on).
 
If the numbers you are getting with the new alt are the same as the old one something is amiss, such as a bad ground, bad or weak wire, or bad connector.

How tight are those battery cable connectors? Are they the stock ones?
 
LittleCaesar said:
If the numbers you are getting with the new alt are the same as the old one something is amiss, such as a bad ground, bad or weak wire, or bad connector.

How tight are those battery cable connectors? Are they the stock ones?
Click to expand...

If the voltage is dropping to 11V at the alternator at idle, then that rules everything else out.
 
Ol'Blue said:
Guess where I got it from hip O'Reilly go figure right so I'll try this again when I get home tonight
Click to expand...

Oreilly, Autozone, doesn't matter, all you're going to get from a parts house is crap. Get your original alternator rebuilt at a good shop and it'll last as long as it did originally. If you've got a compressor and a winch on board, consider asking them if they can beef it up a little, lots of times they can.
 
I'm going ro return the crap alt. and try again. I screwed up when I didn't get the numbers from the old alt. Before pulling it. It really doesn't matter when it's falling almost to 10 amps anyhow.

Going to take some advice and hit the local salvage yard today to come up with another core to have built at the local electrical shop. Great idea.

Blue
 
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