Installed new alt., voltage fluctuates

mpd13078

Registered Member
Original poster
Aug 1, 2014
26
Hello all,
I replaced my original 13 yr. old Delphi alternator with a re-manufactured Delphi. Battery is a couple of years old. I decided to replace the alt. because SEL kept showing electrical code & the TB has stalled a few times in the past when accelerating from a stop. Fuel pump as been replaced along with fuel filter. After replacing it, let it idle for 30 min. - instructions say 20 min.... The entire time the voltage gauge is fluctuating from 14v & higher, especially when holding idle at 2k rpm. The cluster board & electronics, lights (interior/exterior) fluctuating at the same pace. All the codes cleared after I did replace the alt. though.

Could the battery be bad now from the old alternator? I know it acts as a filter in the current wave cycles, right? Maybe I'm seeing the current waves spiking indicating a damaged battery.

Thanks in advance fellow backyard mechanics !!

Mike
 

Tiggerr

Hobbyist
Jun 6, 2013
1,324
Perrysburg, OH
Did you test it with a multimeter or just the dash gauge? I wouldn't trust the dash to be that accurate.
Assuming it is fluctuating. I'd check all the grounds, connections and wires. Have the battery load tested.
Could be you just got a bad unit.
 

BlazingTrails

Banned
Apr 27, 2014
19,409
The first thing I would check is all of the grounds.

Here are the locations of the main grounds that will affect the charging system.

1 under the center console on the larger side.

1 driver side inner fender between battery and fuse block.

1 Passenger inner fender.

1 on b pillar behind the panel where the driver seat belt is located.

There are 3 grounds on the side of the engine under the intake manifold.

Sand each one down to clean metal, apply dielectric grease. See if the voltage stabilizes and report back. I

There are more but I believe those are the main ones.

I hope this helps!
 
OP
mpd13078

mpd13078

Registered Member
Original poster
Aug 1, 2014
26
I just put my meter on the battery & alternator, here are the readings:
battery - to + = 13v-15v fluctuating
alternator positive post to chassis ground = 14v solid
alternator positive post to battery negative = 14v solid.

I have checked the main ground under the driver side frame in the past, due to the electrical problem, but it was good, still had cleaned it up with a wire brush. I'll have to check the rest. Deep sigh.
 

gmcman

Guru
Dec 12, 2011
4,526
You can verify the signal wire is secured on the alternator but it sounds like you may have a bad voltage regulator.

You shouldn't get 15V and I would not try to rev it to see how high it goes.

If you have your meter on the alternator output and a good clean ground and are getting 15V or higher I personally wouldn't drive it, never know how much it will kick out and I don't know how much the platforms electronics can handle.
 

BlazingTrails

Banned
Apr 27, 2014
19,409
With a bad ground you can get high readings of voltage and spikes, but there is a lack of current. I am 90% sure this is a grounding issue. Just my opinion however. :smile:

As a temporary test you can take a pair of jumper cables and try going from the negative battery terminal to a point on the engine to see If the voltage fluctuations changes, and then again to the alternator casing.
 
OP
mpd13078

mpd13078

Registered Member
Original poster
Aug 1, 2014
26
I'm going to start inspecting & cleaning the grounds exposed to the weather elements one at a time first, checking for results after each one. Post results soon, thanks for the ideas & advice.
 
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Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
Also a reminder to have the battery tested.

Just a side note, I had a rebuilt ACDelco that was bad out of the box with voltage fluctuations so it is possible. Check everything else first before condemning the alternator.
 
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OP
mpd13078

mpd13078

Registered Member
Original poster
Aug 1, 2014
26
I went to an alternator/starter re-build shop & they tested both the original & new re-man, both tested good so I put the new one on since it was only $62 with core charge. The battery was bad; voltage output was good, but the CCA was at 479. Upgraded to Duralast Gold-higher CCA. No common auto box store had the correct mounting bracket for their bench machine to test my alternator. I noticed my belt tensioner spring action is squeaky & tight when isolated & I work it which leads me to believe it could be restricting my belt movement because my lights are still fluctuating, oddly enough in rhythm with the up & down movements of the belt tensioner. That's my next replacement. Opinions?
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
You could turn on every possible accessory, including the power hog rear defrost, and see if it slips. If it does, then I'd suspect the tensioner. It could be something else that's not pulling power evenly. As then engine is running and can observe the lights fluctuating, pull one fuse at a time, ex ept for those necessary to run the engine.
 

BlazingTrails

Banned
Apr 27, 2014
19,409
Did you ever make it through cleaning all of the ground locations? Even if your belt was loose your alternator would have to be spinning slower than around 150 rpms to see voltage fluctuations. I do not believe that would be possible or it would be obvious it wasn't spinning with the motor. I'm still leaning towards a grounding issue.
 

05TuckerTB

Registered Member
Jun 7, 2019
12
Tucker, GA
Did you ever make it through cleaning all of the ground locations? Even if your belt was loose your alternator would have to be spinning slower than around 150 rpms to see voltage fluctuations. I do not believe that would be possible or it would be obvious it wasn't spinning with the motor. I'm still leaning towards a grounding issue.
Hey Guys.....where did this issue ever end up? I've got voltage fluctuations that have the dash voltmeter going to near 19V. It was at night with the lights on, no AC. When I got home, went in and grabbed my voltmeter. Measured 17VDC @ battery posts. This has happened before while on a trip. Same voltages were measured since I happened to have my meter with me at the time.

How can I test if the VREG is shot or it's the alternator? I do need to go over all the grounds as suggested in earlier posts to this issue.

Thanks!
 

vipergg

Registered Member
Dec 7, 2011
179
Hello all,
I replaced my original 13 yr. old Delphi alternator with a re-manufactured Delphi. Battery is a couple of years old. I decided to replace the alt. because SEL kept showing electrical code & the TB has stalled a few times in the past when accelerating from a stop. Fuel pump as been replaced along with fuel filter. After replacing it, let it idle for 30 min. - instructions say 20 min.... The entire time the voltage gauge is fluctuating from 14v & higher, especially when holding idle at 2k rpm. The cluster board & electronics, lights (interior/exterior) fluctuating at the same pace. All the codes cleared after I did replace the alt. though.

Could the battery be bad now from the old alternator? I know it acts as a filter in the current wave cycles, right? Maybe I'm seeing the current waves spiking indicating a damaged battery.

Thanks in advance fellow backyard mechanics !!

Mike
It' is always going to fluctuate . It is not steady . Whatever the state of the battery is is determined by the PCM so if it detects that the battery is down a bit it will then charge at a higher rate until it is charged and then you will see it go down . This is normal .
 
Last edited:

05TuckerTB

Registered Member
Jun 7, 2019
12
Tucker, GA
Oh GMTNation Soothsayers, before I shell out $150 for a new alternator, it would be terrific if someone could offer up more detailed advice regarding possible problems in the wiring. Checked the grounds, cleaned like suggested, but having difficulty getting to the back of the alternator. Voltage measured at the battery, cigarette lighter, is 17.5vdc. Every once in awhile dash meter pegs. I know it's a worthless piece of info(lol). Since it's my only set of wheels, taking alternator out for testing is problematic.
Your wisdom and experience and enlighting advice(be nice) would be eternally appreciated.
 

budwich

Guru
Jun 16, 2013
1,719
kanata
check to see if you have a "little black module" on the cabling at the battery ... its a SAVRC which controls regulation. IF you do, unplugged the connector and see what the voltage measurement now is at the lighter. Go from there.
 

Maverick6587

Hobbyist
Dec 16, 2018
730
Sterling Heights, Michigan
After you follow Budwich's steps.

You could take your vehicle to your local parts store. Most of them have a battery and alternator tester that they can bring out to your vehicle to test both at the same time. Not that it's 100% accurate but, it might give you a better/quicker idea of what your problem could be.

I had an ole Kia and I think I replaced the alternator about 5 times (every few months) before realizing that it was the belt tensioner that was causing squealing noises. AZ just kept replacing the alternator under warranty though, because it kept testing low on their mobile alternator tester. :duh:

That was about 20 years ago... Before I had any kind of common sense of engine troubleshooting though. :rotfl:
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
Both great suggestions. The fact that it runs at 17+V, I would be very suspicious of the battery first, then the alternator. Both might be damaged. Just don't wait as you might blow some fuses and damage sensitive electronics at that king of voltages.
 

05TuckerTB

Registered Member
Jun 7, 2019
12
Tucker, GA
Oh GMTNation Soothsayers, before I shell out $150 for a new alternator, it would be terrific if someone could offer up more detailed advice regarding possible problems in the wiring. Checked the grounds, cleaned like suggested, but having difficulty getting to the back of the alternator. Voltage measured at the battery, cigarette lighter, is 17.5vdc. Every once in awhile dash meter pegs. I know it's a worthless piece of info(lol). Since it's my only set of wheels, taking alternator out for testing is problematic.
Your wisdom and experience and enlighting advice(be nice) would be eternally appreciated.
Both great suggestions. The fact that it runs at 17+V, I would be very suspicious of the battery first, then the alternator. Both might be damaged. Just don't wait as you might blow some fuses and damage sensitive electronics at that king of voltages.

UPDATE 6Dec2019:
Thank you for the quick responses.
MAVERICK: I've had those monkeys test it several times at different ones. Due to the wonderful side posts, they often had trouble getting the leads to stay put. After a couple attempts, they give up. I'll try again at a newer store with more knowledgeable staff.

BUDWICH: That explains why the technical diagram that I have that came from this site shows a "Generator Battery Control Module" sitting between the alternator and the PCM, whereas the Hayes book just shows the PCM. I don't have the black box attached to the cables. So assumption is this function was folded into the PCM design in later models?

MOOSEMAN: So battery has open cells? THat would be the only thing that I can think would make charging volts be so high.

The other thought I have to check out is what about an open on the battery voltage input to the PCM? If PCM never sees a voltage does it run the alternator full throttle?

Thank you all for your quick replies. I was cleaning grounds on the fender wells and B pillar.

One more question: the ground under the center console - what side is the larger side? Why couldn't it described in either passenger or driver side? Just wondering:smile:

Thank you.
 

Mooseman

Master Blaster
Moderator
Dec 4, 2011
21,832
Ottawa, ON
So battery has open cells? THat would be the only thing that I can think would make charging volts be so high.

That would be my assumption too. Way back when I was too young and stupid, I ran a car without a battery and the voltage was so high, I blew out just about every light bulb in it. The battery also acts as a buffer to absorb and regulate that power and without a battery (or with an open cell), the voltage regulator doesn't see a proper voltage and just goes hog wild.

Without a SARVC, the alternator works like a normal one, keeping the voltage at a constant ~14V. The SARVC would throttle down the alternator output and voltage according to actual amperage demand of the battery and systems so it would be normal to see voltages between 12.6V and 14V while running. This was to reduce overcharging the battery and extend its life. These were added to later years, IIRC starting in 2006.

The other thought I have to check out is what about an open on the battery voltage input to the PCM? If PCM never sees a voltage does it run the alternator full throttle?

All the PCM does is tell the alternator to charge or not (on/off). This is most notably seen in very cold temperature where the PCM will wait a few seconds before commanding the alternator to start charging. This is guessed to be a safeguard to the belt to limber it up before dumping a bunch of stress on it. The alternator's voltage regulator still regulates the voltage.
 

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