1999 gmc sierra 2500 volts surging

[untouchableone]

So when its just idling at a light or even in park my volts surge from 14 down to like 9. My fuel pump is noise an it makes a different whine when the volts drop. Is this a fuel pump problem? Has new battery an newer alt. 6.0 vortec

[untouchableone]

Also my battery light comes on for a sec under heavy acceleration

[8.1HD/ALLISON]

Have the battery and alternator tested. Doubt its fuel pump. Sounds like fuel pump noise is reacting to voltage drop.

 

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[untouchableone]

Can they test the alt on the truck?

[Spurshot]

yes

[untouchableone]

Forgot I had a volt meter. So battery was 12.7 with truck off. Started it an it went up to 14.6

It was surging an going down to 12.6 an up to 14.6. Turned everything on an it just did same thing.

[untouchableone]

Voltage regulator?

[untouchableone]

Fuel pump also makes the noise while driving but volts dont surge.

[sdeeter19555]

Forgot I had a volt meter. So battery was 12.7 with truck off. Started it an it went up to 14.6

It was surging an going down to 12.6 an up to 14.6. Turned everything on an it just did same thing.

 

Sounds like alternator issues...

 

Voltage regulator?

 

I want to remember the GM alternators are internally regulated?

 

Fuel pump also makes the noise while driving but volts dont surge.

 

Coincidental..the fuel pump would pop a fuse before it pulled enough to cause the draw down you are seeing. I would suspect the fuel pump is also failing, and may be failing because of the voltage fluctuations.

[untouchableone]

Yea I think they are. Ok maybe ill buy a alt.instead of doing water pump

[sdeeter19555]

They can test the alternator off the vehicle...how many miles do you have on the truck?

[untouchableone]

260k alt looks newer.

[00Silverado4x4]

I would definitely have the alternator tested prior to doing anything else for diagnoses. If I recall even in the '99 model the volts are going to flux a little bit due to the system the way the alt is desined. As in when it doesn't need to charge it "shuts off" then when a load is applied it should reingaged and charge. If you started the truck and the voltage dropped and stayed there I'd say you need a new alternator as well.

[untouchableone]

Mechanic tested alternator and he says its the fuel pump drawing the power. so I dont know guess ill try the pump since I aalready bought one