Bad alternator?

[DesertRat]

While towing my TT home on Saturday, my alternator started making a terrible noise. Like a blender eating itself. Out of a fear of being stranded on a hwy in BFE I decided to locate one and replace it. It failed the two checks on the Vatozone scanner. Note, I did not observe any erratic readings on the dash board voltage gauge. The store only had a Duralast reman'd 160 amp so I went with that. Same model # that was on there previously actually.

A couple hours in, I notice the voltage drop to 11.5V (my estimate). I pull off the fwy and restart the vehicle. Guage indicates a little above 14V and then settles right at 14V while driving. No issues, until the RPM's jump when the transmission shifts down to 2nd from 3rd. After a couple of seconds the voltage drops. Once I ease off the throttle and the transmission shifts to 3rd, the voltage settles back at 14. I noticed this behaviour a few other times while pulling a hill or passing. Voltage drop with high RPM's in 2nd and 14v with all other conditions. Is the alternator bad?

Doesn't seem like belt slippage since the only change is the alternator. And my driving habits stayed the same.

 

[strutaeng]

The voltage fluctuates a lot I've noticed, and my guess is it depends what electrical stuff is on (external load like lights, but maybe on the load required by the powertrain like transmission control solenoids) and engine RPM. Alternator duty cycle is controlled via PWM through the computer. Did you just buy the rig? Maybe you just hadn't noticed?

Sounds kinda normal to me, but maybe someone else may chime in and confirm.

 

[DesertRat]

I monitor my gauges pretty regularly since I generally pull several grades while towing as well as run through desert sections. I've not noticed anything that extreme. Prior to that stop I had many gear drops to 2nd over the course of a few hours as I battled a head wind. There was minimal if any fluctuation.

 

[Fless]

Look up "RVC" and/or check this thread:

Figured out how to keep steady voltage

on the 07+ we have this regulating system (Regulated Voltage Control or RVC) that basically controls the alternator when it sees more/less drain on the battery. Being that I have a decent sized stereo as well as HIDs (with the relay harness) on my truck, I looked for a way to turn the RVC off...

www.tahoeyukonforum.com

 

[Joseph Garcia]

^^^^^x2^^^^^

 

[DesertRat]

Look up "RVC" and/or check this thread:

Figured out how to keep steady voltage

on the 07+ we have this regulating system (Regulated Voltage Control or RVC) that basically controls the alternator when it sees more/less drain on the battery. Being that I have a decent sized stereo as well as HIDs (with the relay harness) on my truck, I looked for a way to turn the RVC off...

www.tahoeyukonforum.com

Thanks. Will keep that in mind. My only change was the alternator and it's the first time I've had this issue. Forgot to add that it kicked on a service charging system message. I drove the vehicle (sans trailer) this morning keeping it in first and second, along with 3-2 drop, no issue. Gonna swap the belt to be sure and check wiring where I was working. Thanks for the input guys!

 

[Foggy]

Could also just be a poor replacement part that doesn't play well
with the OE programming...
I went with an original GM part when I did mine a couple years ago due
to the bad comments on the aftermarket parts store's replacements

 

[mikez71]

Look up "RVC" and/or check this thread:

Figured out how to keep steady voltage

on the 07+ we have this regulating system (Regulated Voltage Control or RVC) that basically controls the alternator when it sees more/less drain on the battery. Being that I have a decent sized stereo as well as HIDs (with the relay harness) on my truck, I looked for a way to turn the RVC off...

www.tahoeyukonforum.com

Yep, if it still happens, disconnect the RVC sensor to check. I have heard of a couple going bad.