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Problem with voltage fluctuations

tlocus

By tlocus
in Ask A GM Technician

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tlocus Enthusiast

tlocus

Posted
Posted

Hi,

I just started having some voltage fluctuations (according to to Volt gauge).

Truck is running idle at normal operating temps.

I notice the volts on the gauge drop from 14.6V (Which I think is the normal running volts?) down to maybe 12V then back up to 14.6V.

At the same time I noticed my oil pressure gauge, at idle jumps around a few psi(but other than that seems to work, more rpm more psi and at idle drops back down).

And at night with my lights on, when press my window switch or any other powered accessory the lights dim out.

 

Any ideas? Alternator going bad, battery...?

 

Also seemed to have developed an small oil leak running down the oil filter.

I did change filters from AC delco to mobil 1 but still have the leak. Even tried tightening the oil pan bolts around the area.

 

t

mmmikkke Senior Enthusiast

mmmikkke

Posted
Posted

If your alternator is intermittent, you'd see exactly what you see, it'd go from charging (14v) to not charging (12v).

 

But this could also happen if the load on your electrical system is high, and you're just idling. Say the headlights are on, the heater/ac fan is blowing, and a few other minor accessories are running, you could probably draw more amps then your alternator can produce at idle, and your volt reading would drop to 12 or even lower. It's not impossible to read 12v or less at idle and nothing's wrong.

 

Is the fluctuation happening during the day, while cruising at road speed? If it is, you definitely have a problem. Probably the alternator.

 

For the oil filter area leak, do you reach up and wipe off the filter mating surface when you change the filter? You're supposed to do that. Use a clean paper towel, and wipe carefully so any dirt that you wipe is wiped toward the outside of the filter sealing surface. After you wipe it, it should be completely clean shiny silver metal.

stefano462 New Member

stefano462

Posted
Posted

Make sure you also check the positive battery cable for corrosion, particularly near the positive battery terminal end. That too can give you voltage flutter.

 

You will have to get creative in removing the red cover off of the cable end. If you need a new battery cable, it is an AC-Delco or dealer part only. You can get one from an AC-Delco parts shop for about $70. I just went through a similar problem and this was the solution with my 2000 Suburban. I can get you the part number if you need it.

Halen5150 Enthusiast

Halen5150

Posted
Posted

Your alt is probably going bad. I just went through a similar experience. Sometimes the voltage would jump around, and sometimes it would hold constant around 14V. Replaced the alt, and now everything's gravy. That's my guess.

  • 1 year later...
ffffred New Member

ffffred

Posted
Posted

I can't tell you the heartache I went thru with a 96 Tahoe until I finally replaced the side terminals with top terminals. Suffice it to say that the engine missed out, the positive terminal oxidized constantly and I was constantly tightening them, and diagnostics just told mechanics that I had "a short circuit." It was just poor engineering, plain and simple.

 

PS, I just went down to the auto parts store and bought traditional "clamp" terminals, sawed off the old ones. You need a battery with top terminals on it.

  • 3 months later...
dlknight Enthusiast

dlknight

Posted
Posted

Hmmm my 94 Jimmy is charging at 12.25 volts. I have a new battery and alternator. The IGN/GAU fuse blows also. Not sure if that is part of the same problem.

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