Voltage Problem?

[VTJosh]

While driving the other day all my lights on my dash dimmed and I noticed my voltage gauge drop down between the 9 and 14. It's normally always above the 14 mark. When you get on the gas it doesn't move at all but when you "coast" it jumps above 14 but drops as soon as you step on the gas or brake. My battery light came on at this time. Since the truck never died, I said screw it and parked it. Next morning it started right up, no battery light but same voltage problem. Was driving home after work and the battery light came on again. Figured alternator was on the way out so went to Autozone and had them test it by holding at 2k rpms. There test came up fine so they did a battery test and it came up as "low charge" Figured the battery has gone bad being 41/2 years old , I bought a new one. Same damn problem. Even though the alternator tested fine I may get a new one but the truck came with a 130amp as part of the plow package and there pretty expensive. Checked battery cables and the cable on the back of the alternator and there good. Is there anything else that could cause this issue?

 

*Edit* Truck is a 2000 Silverado 2500 6.0l

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What usually happens is overtime your throttle body gets dirty. This lowers your idle speed in unnoticeable amounts, overtime it gets so low that right when you let of the gas coming to a stop your alternator goes off line for a second and then comes back up thus dimming the lights. It is really noticeable at night with the headlights on. Clean your throttle body or speed your idle back up and I bet it will go away.

[VTJosh]

Lol, funny thing is that I just did that yesterday. Wasn't because of my voltage problem though, I just figured it was dirty and in need of a cleaning lol. I idle right aroud 500 rpms.

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Yep, that's the exact same engine as mine. As long as it's idling around 500-600 and doesn't dip down a little when you let off the gas sometimes, the alt shouldn't "blackout". I doubt it's the alternator, since it still charges, just goes off line sometimes. And the alt tests at autozone, or wherever, are a joke unless the alt is totally shot. But, my truck does that too, just for maybe one second almost every time I come to a stop, but the bat. light has never came on.

[VTJosh]

From reading around I saw "voltage regulator" mentioned a few times. Not sure if it's built into the alternator or something seperate though?

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Voltage regulator is built into alternator, if it failed the volt gauge would always read a high value like what it does when you crank it up when it's cold.

[Willshire]

Try probing the fuses with a multimeter set to ohms or continuity(same thing). A zero means you have a short somewhere but the fuse detail should tell you what is shorting. Disconnect pos terminal of battery.

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Try probing the fuses with a multimeter set to ohms or continuity(same thing). A zero means you have a short somewhere but the fuse detail should tell you what is shorting. Disconnect pos terminal of battery.

You forgot to tell him to remove the fuses or they will all show 0 ohms, if they're not blown that is. I really really doubt it is a short of any kind as my truck does the same thing too, I just live with it.

[Willshire]

Try probing the fuses with a multimeter set to ohms or continuity(same thing). A zero means you have a short somewhere but the fuse detail should tell you what is shorting. Disconnect pos terminal of battery.

You forgot to tell him to remove the fuses or they will all show 0 ohms, if they're not blown that is. I really really doubt it is a short of any kind as my truck does the same thing too, I just live with it.

 

 

i guess i should have stated to probe between ground and the fuse. This way it is not necessary to remove the fuse or else you will have to probe both sides where the fuse plugs in low resistance between ground (10+ ohms) may just be a resistive load but, that depends on the fuse you are probing. A zero would result in a blown fuse but if its low resistance on a large fuse it may not blow. I am sure you are right about it not being a short but, a bad or corroded ground could cause dimming, if it is excessive (battery light). Clean frame ground points and engine block ground points and clean battery terms and see what happens.

[VTJosh]

I'll go through and clean up every ground wire I can find.(I only checked the wires coming off of the alternator and battery) Any one in particular to check? I do have a very small oil drip when the trucks warmed up so it's possible one under the truck got hit with oil. I'll check my fuses aswell.

[VTJosh]

Just to update this for everyone. The following day after my last post, on my way to work my volts started dropping even more and the truck died. Walked my fatass to Advanceauto, bought a new alternator, carried the pain in the ass back to the truck a few blocks away and swapped it out with a 15mm wrench, flathead screwdriver and vice grips. Those were the only tools I had on me but they got the job done. Truck has been perfect ever since. So after all this I've come to learn, DO NOT TRUST AUTOZONE'S ALTERNATOR TEST, lol. Thanks everyone for the other ideas.

[Wires]

Just to update this for everyone. The following day after my last post, on my way to work my volts started dropping even more and the truck died. Walked my fatass to Advanceauto, bought a new alternator, carried the pain in the ass back to the truck a few blocks away and swapped it out with a 15mm wrench, flathead screwdriver and vice grips. Those were the only tools I had on me but they got the job done. Truck has been perfect ever since. So after all this I've come to learn, DO NOT TRUST AUTOZONE'S ALTERNATOR TEST, lol. Thanks everyone for the other ideas.

 

I guess you get what you pay for then (free).