SOLVED! Alternator voltage spiking after 3 replacements

[gmcman]

With my 2012 Yukon, I'm getting voltage spikes as well as uneven voltage on moderate to heavy acceleration. My headlights will noticeably flicker when this happens and the voltage will spike to around 15.2-15.5V...almost like it's bumping a rev limiter at half that frequency.

I did rinse my engine the day prior to my alternator going bad, I am careful to not soak the alternator or PCM.

No loose cables, even happens when I disconnect the connector on the NEG battery cable for load shedding.

I'm curious to understand if the PCM or alternator or both, regulate the voltage on this platform.

I have tried 2 alternators from Autozone and one from NAPA, am I just that unlucky? Lol.

All thoughts appreciated.

 

[mrrsm]

This Article is On Topis and Interesting...

Voltmeter fluctuates GM Trucks? (The answer is found) - Belle Haven Shell

GM says fluctuating voltage on the vehicle’s voltmeter is NORMAL and is not a reason to replace any parts. The TSB applies to 2005-08 Cadillac Escalade, 2005-08 avlanche, Silverado, Silverado Classic, Suburban, Tahoe, 2005-08 GMC Sierra, Sierra Classic, and Yukon. What causes a voltmeter to...

belleshell.com

The Related Video is VERY Detailed...

 

[gmcman]

Watch the beginning, then FF to 1:06.

The fluctuating voltage I see under normal cruise seems fine, it's the hard spikes that are flashing my lights.

 

[mrrsm]

Just to make certain...have you replaced your Serpentine Belt Tensioner vs. the one installed at the Factory? If not... THAT item can cause weird Belt Tension issues if it suffers from any "Slips-N-Grabs".

 

[Mooseman]

I'd be checking all the connections to the battery and the grounds. Maybe a main ground is corroded or loose. Check the connections on the alternator. I once had a faulty connector on the alternator that wouldn't "click" in properly. Had to trim the plastic a little and it then held firm. Maybe wiggle wires while you watch the voltage.

 

[gmcman]

Just to make certain...have you replaced your Serpentine Belt Tensioner vs. the one installed at the Factory? If not... THAT item can cause weird Belt Tension issues if it suffers from any "Slips-N-Grabs".

I have recently replaced the tensioner with an OE GM but the belt is old....I will replace the belt.

I'd be checking all the connections to the battery and the grounds. Maybe a main ground is corroded or loose. Check the connections on the alternator. I once had a faulty connector on the alternator that wouldn't "click" in properly. Had to trim the plastic a little and it then held firm. Maybe wiggle wires while you watch the voltage.

I will double check and clean them.

Here's a video I took tonight, I included both voltage parameters from Torque, OBD on left, and Command Module on right.

 

[Mooseman]

Looks like a loose connection. It loses the voltage from the battery and tries to compensate.

So that's while driving. What about if revving while stationary? What about power braking? (holding brake, putting in Drive and pushing throttle). I'm thinking that engine movement is causing it.

 

[mrrsm]

Amen... and Engine Grounds can be firmly attached to the Block... and STILL be Badly Corroded:

 

[gmcman]

Looks like a loose connection. It loses the voltage from the battery and tries to compensate.

So that's while driving. What about if revving while stationary? What about power braking? (holding brake, putting in Drive and pushing throttle). I'm thinking that engine movement is causing it.

It absolutely acts like a loose connection. However, this started after the OE alternator flaked out, I only removed the NEG cable at the battery, and the alternator connections, nothing is loose.

I did remove the ground cable today from the engine, sanded it down, moved the two prongs slightly on the signal connector for a good tight fit, same deal.

I tried power braking it, didn't get the high spikes but a lower erratic spike but only from about 12.8 to 14V...nothing like when I'm driving.

The belt theory is a good one, but what would allow 15.8 VDC? That has to be the regulator correct?

 

[mrrsm]

The Wiring Harness leading To & From the Alternator might also deserve a Very Close Inspection... looking for something like THIS:

Check Out How Well the Connector is Attached to the Harness bolted to the Alternator for Subtle Corrosion, too:



Different After-Market Alternator Manufacturers might have variations on the A/C to D/C Rectifier Diodes and Electronics that may NOT limit the current within the correct Prescribed Range... So Researching their Product Specs PDF might be more revealing.

One more suggestion... Of ALL the recent encounters for HTIAL (Hard To Identify And Locate) Strange or Transient Electrical or Electronic Issues... Using a LABSCOPE (Inexpensive Oscilloscope) to perform VERY In Depth Voltage and Amperage Behavior Analysis is THE Preferred Tool in any such cases.

This is based upon the fact that a mere Dash Mounted Volt Meter is incapable of taking a High Enough Sample Rate or when likewise, using the Typical DVOM or DMM because the Readings get AVERAGED, vs. Observing the Very Finely Detailed Captures that either a PICO-Scope Model #2204A or a Hantek Model #1008C can capture, SELECT AND ZOOM IN ON and then display the Important Data onto the Laptop Screen as Voltage Over Time events when being Viewed in Exquisitely Detailed Diagnoses.

THIS Video Demonstrates these possibilities:

You should SEE...What You Are MISSING... :>)

How To Use PICO #2204A & HANTEK #1008C Oscilloscopes

You don't need a Huge Bag of Coins in order to obtain and use an Oscilloscope for performing In-Depth Wave Form Analysis in Automotive Applications on everything from Problematic Electronic Fuel Injection to obtaining accurate Compression Tests to Diagnose Internal Engine Conditions. HANTEK...

gmtnation.com

 

[Roudter]

I wash my engine too. But it's critical that you blow the compartment immediately with either a leaf blower or compressed air. I found a leaf blower actually clears the entire area of water better. One time I did not do the air thing and my cooling fans (or something nearby) started to smell very electrically compromised...I got on the highway and that was over a year ago. So, you gotta blow that water out...espsecially with modern cars

 

[gmcman]

The Wiring Harness leading To & From the Alternator might also deserve a Very Close Inspection

Wiring does look very good, no corrosion either.

Here's a vid of the ripple, I remember being under 200 mV is good, his video was good info.

Mine jumps to over 400 mV a few times during power braking. Even follows the slower frequency of the flickering when not driving and only power braking.

 

[mrrsm]

It's "NO FLUKE" that your Meter is VERY Nice and Full Featured... and while you've already got this Product PDF... I'm linking it below for anyone wanting a decent DMM like yours. Nonetheless...it would also be nice to have another Video with the mV Spikes On Screen with the Varied Engine RPM...while also noting which "In Cabin" Features are being turned On and Off to possibly identify a problem external to the Battery and Charging System. Good Science Means ... Only Change One Variable at a Time. :>)

This was the Highest Recorded A/C mV Spike in your Video:



There IS one other aspect that deserves looking at: The Length of The Serpentine Belt. Over the years, I've developed a very jaundiced view of making any uninspected purchases from OTC Stores where people get the opportunities of 'Handling' (...think 'Swapping'...) the Merchandise... leaving the "NUB"s (Next Unsuspecting Buyers) the chance to Buy The Wrong Parts, Belts, etc. ( Ask Me How I KNOW).

BIG Performance Problems can emerge if the Serpentine Belt is even slightly longer or shorter than the OEM inside and outside dimensions making the RPM of the Generator Shaft spin more or less per RPM (Versus Measured Engine RPM and Output from the VSS) than it should.

 

[filthyfingers]

I wash my engine too. But it's critical that you blow the compartment immediately with either a leaf blower or compressed air. I found a leaf blower actually clears the entire area of water better. One time I did not do the air thing and my cooling fans (or something nearby) started to smell very electrically compromised...I got on the highway and that was over a year ago. So, you gotta blow that water out...espsecially with modern cars

Blow drying your engine after a (pressure?) wash does not seem critical to me. I pressure wash my ‘02 Envoy and kids BMW a few times a year. Clears out the salt, soil, oil, pine needles, squirrel deposits,etc. Never had an adverse effect.
But it sounds like a good idea. Next time I’ll add a blow dry to the beauty treatment. Thanks.

 

[gmcman]

Nonetheless...it would also be nice to have another Video with the mV Spikes On Screen with the Varied Engine RPM...while also noting which "In Cabin" Features are being turned On and Off to possibly identify a problem external to the Battery and Charging System.

If time permits I can try with a GoPro but may not be able to. I have a new OEM AC Delco alternator arriving today and when I get it swapped I'll update this.

I thought I pressed "Reply" so the above was not sent...sorry.

I installed the new OE AC Delco alternator last night and all is good. @Mooseman I also could swear it was a loose connection somewhere given the evidence, and the fact it happened with 3 other alternators.

Not one flicker.

 

[Mooseman]

Is that a new or rebuilt ACDelco? I've had problems with a rebuilt and when I went with a new aftermarket Chinesium, it was flawless. Glad you got it figured out.

 

[gmcman]

Is that a new or rebuilt ACDelco

Brand new.

 

[mrrsm]

It's even Sweeter, when You managed to get the Banner Under Your OWN OEM Steam. :>)

 

[mrrsm]

If you have no objections... THIS is another Video from Eric "O" from SMA (South Main Auto) where a Chevrolet Silverado Z71 Truck got dropped off in his yard with the Infamous "List" and among so many other problems ...the OP had a replacement Alternator installed on the Engine that may factor as related to this Thread Scenario where certain years around 2012 had issues with the Alternators "Cutting Off Suddenly". AND Eric "O" provides a NICE, LONG LOOK at the GM Paper Documentation about their response to the Damned Issue.

FWIW... His stuff about our Beloved Chevy Trucks always proves worth knowing: