Voltage up and down. 87 2f (1 Viewer)

[60Man]

So I am starting here. I have a 87 fj60 that is otherwise running very well. I. Am having voltage drops while driving. They are going from a 13 or 12.5 down to a 10 or 9. I am watched the dash volt meter and an extra one that I installed.
The truck drives smooth with any volt. It will change regardless of driving conditions. I can be cruising at speed and it will change every 5 min or so. I did take the battery to a shop to get tested, the gave it an all clear. I did change the terminal connectors, the had a small amount of rust. I did trim the cables back for a fresh connection. Thank you.

 

[Beams37]

A few thoughts. It could be a bad gauge or a bad ground. Could also be a failing alternator or even alternator part (like voltage regulator) that is impacting the voltage.

 

[PeterEdm]

A few thoughts. It could be a bad gauge or a bad ground. Could also be a failing alternator or even alternator part (like voltage regulator) that is impacting the voltage.

Had a similar issue with my HJ60. One of the brushes was worn right down while the other one was in good shape. Replaced bad brush and charging went back to normal.

I had previously replaced voltage regulator prior to investigating brushes. Wish I had checked those first, would have saved me a good chunk of chance.

 

[Seth S]

If your alternator is failing you likely will see the battery light flicker or turn on while you are driving. Your gage might be the problem as well. Before I went to crazy I’d wire in a cheap digital voltage gage and see if its readout matches your gage. If it does then it’s time to check

Battery terminals for clean and tight
Battery cable condition
Fusible link condition
Wires at alternator condition.
If everything looks good it’s time to suspect the alternor. I haven’t looked in a while but rock auto used to sell one for $60 that works well. Otherwise @ToyotaMatt might have a super nice OEM unit to throw in.

 

[OSS]

Verify if the voltage is actually jumping around and it’s not just a malfunctioning dash voltmeter.