Strange Voltage Fluctuation / 1995 Yukon

[BigBen]

Ok, I've been chasing some voltage gremlins (low voltage, engine cutting out) lately and gave up and dropped in a new Interstate Battery and had my Alternator rebuilt.

I put the parts in yesterday and checked the voltage drop across the terminals. Alternator to battery has about a .1 volt drop on the positive side and about .05 volt drop on the ground side. I'm pretty sure I've got good connections and I cleaned everything up before reassembling.

So, today the voltage starts dancing all around on my gauge from 'normal' to higher and back.

For reference here, the numbers on the gauge are NOT quite correct. (Have changed over time.)


Battery voltage of 12.6 reads:



While running at a normal charge level (~14.5 volts) it looks like this:



What I saw today:

I was able to check with a multimeter and '14' on the gauge reads 15.2 on the meter.

Oh, and I'm pretty sure it is NOT a gauge problem since I can hear the blower pitch/speed changes as the voltage fluctuates.

I'm honestly not sure what to think. If it were a bad connection, I'd expect the voltage to drop, not climb like this does.

Anyone got some insight as to what is happening here?

It doesn't matter if I'm idling at 600rpm or running down the freeway at 2000rpm, it will do it. However, it is intermittent but seems to be happening more and more often.


As usual, any and all help is appreciated!

-Ben

 

[Fordum]

Usually its a bad ground when you start seeing stuff like this.
Check the ground connection from the battery.
Its the "return" to the alternator. If the alternator does not see the battery, it has no ground reference in many cases, and the voltage will go high.

Sounds like the alt is grounded to the truck, so the truck is seeing its output, but the battery is not in the circuit all the way.
However, since its a new alt, you have to be suspicious of it also.

I'm making the assumption that its an internal regulator. If not, check the ground on the regulator.

I would pull the ground terminal on the battery, just in case. Even though its a new battery and you cleaned them when you installed it. Double check it to see if its clean and the wire to clamp connection is good.

Then, run a temporary ground wire to the case of the alt. Come directly off the battery.
Be careful, if it is a bad ground you might get significant current in that wire. Use a fairly heavy one.

 

[imiceman44]

I would definitely check the grounds like fordum said, but since you just replaced the Alt I would have it checked too.
Now when you say you had been chasing gremlins before you changed the alt did you have that same problem or is this problem new?
As for grounds, you want one from engine to chassis, one from battery to chassis, one from battery to engine, and one from chassis to body, and if you have the patience also one from engine to body.

Ok, I've been chasing some voltage gremlins (low voltage, engine cutting out) lately and gave up and dropped in a new Interstate Battery and had my Alternator rebuilt.

I put the parts in yesterday and checked the voltage drop across the terminals. Alternator to battery has about a .1 volt drop on the positive side and about .05 volt drop on the ground side. I'm pretty sure I've got good connections and I cleaned everything up before reassembling.

So, today the voltage starts dancing all around on my gauge from 'normal' to higher and back.

For reference here, the numbers on the gauge are NOT quite correct. (Have changed over time.)


Battery voltage of 12.6 reads:

View attachment 119543

While running at a normal charge level (~14.5 volts) it looks like this:

View attachment 119542

What I saw today:

I was able to check with a multimeter and '14' on the gauge reads 15.2 on the meter.

Oh, and I'm pretty sure it is NOT a gauge problem since I can hear the blower pitch/speed changes as the voltage fluctuates.

I'm honestly not sure what to think. If it were a bad connection, I'd expect the voltage to drop, not climb like this does.

Anyone got some insight as to what is happening here?

It doesn't matter if I'm idling at 600rpm or running down the freeway at 2000rpm, it will do it. However, it is intermittent but seems to be happening more and more often.


As usual, any and all help is appreciated!

-Ben

 

[MNorby]

had some problem with my 97 sonoma, engine would cut off instantly periodically. Batt voltage and everything under the hood has a solid 12v but the volt gauge in the truck would drop to 5v or so when it acted up. Ended up being the starter ignition switch. Found if I smacked the key it would go back to 12v on the gauge and smack again and it would go back to 5v and engine would cut. Check and see what voltage you have on your fuses and see if one is low then look at the circuit, I bet it might be the IGN circuit.

 

[BigBen]

Now when you say you had been chasing gremlins before you changed the alt did you have that same problem or is this problem new?

As for grounds, you want one from engine to chassis, one from battery to chassis, one from battery to engine, and one from chassis to body, and if you have the patience also one from engine to body.

THANK YOU everyone for input. I really need to figure this out. This is still my DD for business and I am going almost crazy.

First answer: This problem is new since the Alternator was 'rebuilt'.

I'll give a little history here, but it will take a little bit of explanation. Please bear with me:

Purchased truck in 1998 with 57,000 miles with Alternator "A".
-As far as I know, this was the original Alternator.
Many happy years driving the truck with the normal maintenance.

2004/185,000 miles: I replaced original Alternator "A" with Reman Delco alterntor "B" for a remote Quebec hunt. (Preventative maintenance)

2010/265,000 miles: I started having some intermittent problems with the ignition cutting out. Had been noticing the voltage reading lower than normal, but checking showed voltages fine and gauge seemed to be 'offset' but still working. Eventual change of Pickup coil appeared to cure intermittent problems.

June 2010/270,000 miles: 7 year old battery gave up the ghost. New DieHard gold put in. Low voltages seem to be better.

Late 2010/275,000 miles: More cutting out and strange problems. In a fit of rage, original Distributor replaced with Delco reman unit. Everything good!

Spring 2011/280,000 miles: Voltages reading VERY low on a trip home and truck cutting out. Suspicious of voltages, I pulled Alternator "B" and put Alternator "A" (known good) back in. Voltages were normal and no more ignition cutting out.

Took the alternator to a local alternator shop in Muskegon and they said Alternator was good. Tested battery as 'bad' and recommended replacement. During this I found corrosion on the positive battery terminal and cleaned it up. Took battery to Sears and they said battery was 'fine' after they charged and tested (11 month old battery/they may not want to warranty). After this the voltages were reading find and everything was happy. I attributed the problems to the corroded connection and went on my merry way.

As a precaution, I had alternator "B" rebuilt (bearings and such) so I could swap it back on for "A" when I had time.

July 2011 / 285,000 miles: Alternator "A" is still in the truck, but the operating voltages are dropping. Noticing that on the freeway I'm dropping to 'battery voltage' when the blower and lights are on. At a stoplight I can't run the blower and lights or I drop below 12v. No fluctuations like the video. Voltage just drops under load and low RPMs.

Tired of the mess, I bought a new Interstate battery and put it in, as well as Alternator "B" which was repaired recently. The ‘repair’ was mechanical and I believe all electronics were tested and NOT replaced.

Everything looked great! Voltages were normal when operating, no fluctuation, and I could sit at idle with the A/C, radio, and lights on while maintaining a charge voltage. VERY happy.

That worked for about 150 miles. Then the fluctuations 'UP' started happening like in the video. (This is new) They got more and more frequent over the next 50 miles to the point that they were regular and continual. Last night it was so bad the truck threw a 'battery' light and I could watch the lights pulse as the voltage changed. Once again, NOT CUTTING OUT.

This morning: Pulled freshly rebuilt Alternator "B" and dropped old Alternator "A" in and drove to town. NO FLUCTUATIONS like the video. However, the voltage did drop somewhat at stoplights. (Similar to what it was doing before removal.) The fluctuating problem now appears to be GONE.

I have not had a chance yet to go clean grounds. However, I did check voltage drops again:

Battery (+) to Alternator (+) was 0.10 volt while running. (*good)
Battery (-) to Alternator chassis (-) was 0.03 volts while running.(*good)
Battery (-) to body ground in fender (-) was 0.03 volts while running.(*good)
Resistance from Battery (-) to fender bolt (-) was 3.4 ohms with truck off, but battery connected.




Well, there you go. The full rundown on how I got here and what I'm seeing.
If you've made it this far, I'd love to hear your thoughts! Right now I think I'm taking my alternator back for a check and looking at cleaning all my grounds this weekend, just to be safe.

Thanks for reading!

-Ben

 

[dhcomp]

Never hurts to add additional body to frame, frame to engine, etc. grounds.

The factory block to body ground strap kinda sucks.

I buy the biggest walmart battery cable i can find, cut in half, add new lugs on cut ends, and have 2 cables for cheap . I ran from body to frame, and frame to motor with additional ground cables.

Really steadied the gauge reading on my Blazer, as well as brought it up to closer to a true reading.

 

[BigBen]

Also, please note in the video that the voltage at '14' on the gauge is HIGHER than normal, as sown in the photos above.

'14' on the gauge is 15.20 or higher on the multimeter.

My fluctuations are 'up' from 14.5, not down.

The video is somewhat misleading because it starts at 14 on the gauge. That's just where I caught it when I started recording.

View attachment 119543

While running at a normal charge level (~14.5 volts) it looks like this:

View attachment 119542

What I saw today:

 

[BigBen]

Never hurts to add additional body to frame, frame to engine, etc. grounds.

The factory block to body ground strap kinda sucks.

I buy the biggest walmart battery cable i can find, cut in half, add new lugs on cut ends, and have 2 cables for cheap . I ran from body to frame, and frame to motor with additional ground cables.

Really steadied the gauge reading on my Blazer, as well as brought it up to closer to a true reading.

Yeah, it's looking like a fun weekend 'strengthening' all my grounds, just to be sure.

 

[BigBen]

I do find it interesting though that replacing the 'new' alternator resulting in the fluctuations going away (at least so far).

 

[Fordum]

Sounds like the alt B is part of the problem. Maybe all of it.

Measuring ohms with a battery in the circuit is problematic at best even if there should not be any voltage.

You have the right idea with measuring voltage drops, but those measurements are only useful if taken under heavy load.
Turn the truck off, and turn on every load you can find. Headlights, fan, radio.
Then measure the voltage drop from the battery negative to the fender bolt.
3.4 ohms is way too high, but may be a false reading. Voltage drop will tell the tale.
Also, when under heavy load with the engine off, measure from the post to the clamp on both positive and negative posts if its a top post battery.
This will tell you the quality of each clamp connection.
Then if you can reach, measure from the positive post to the post on the starter solenoid where the heavy wire hooks up.
Same from the negative post to where the negative wire hooks up.

Much more than a .1 of a volt any of those places indicates a problem between the two probes.

The measurement between the alt.+ and the battery+ is only valid if there is a heavy load there.
Try it with the engine running and everything turned on.
Same as the alternator- and battery-

Having the voltage drop to battery voltage at idle is common when the alternator is worn or too small to handle the load.
I think alt A is good, just too small or worn.
A fan pulls a lot of power. I have a fairly hot alt. in my Ford truck, but if I turn the fan on high and high headlights, it will go to battery voltage on a hot day at idle.

BTW, I had the dash out for something else, and calibrated my voltmeter while I was in there.
I hooked a known voltage to it, and then carefully twisted the needle on the shaft until it matched.

Sounds like B has a bad solder joint in the regulator.
Probably not going to show up except under vibration or heat.

If the shop you took it to is a complete alternator rebuilder and knows how to custom build one, take it back to them and tell them about the intermittent electrical problem.
Bet they can find it.
If they are just a generic rebuilder, don't bother unless you have a warranty with them.
We have a shop here that has been in the generator/alternator business since about 1930, and they are experts.
They would have no problems with that alt.
There are other places around town that will rebuild one by putting in new bearings and brushes, with a load test, and they could not handle it.

 

[Fordum]

A cold solder joint on the internal regulator would cause it to output low or high depending where the joint was.

 

[BigBen]

Thanks Fordum for your response (as well as all the others)

I should have thought more about Ohm's law before checking all those circuits. I'll make sure the current is flowing heavily before I check it next time. Too much Mech-E, not enough EE.

The shop in town has a good reputation, but I think you're right. I need someone who 'knows their craft' rather than a part changer on this Alternator. First impression is that they'll be able to handle it, but you never know.

I'll give it a shot. At the worst I'll tell them that I want a new voltage regulator.

It will be Sunday before I can go through everything, but I'll post up once I've got more data and findings to share.

Thanks!

-Ben

 

[Fordum]

It could be a bad solder joint elsewhere, like one of the brush connections or diodes, but I cannot think of anywhere offhand that would make the voltage go up except for the voltage regulator.

AHH, its nice when someone I am explaining it to understands all of the aspects of Ohm's law and how voltage drop changes with current.

There is no telling how many cranking problems I have diagnosed for people with top post batteries just by turning on all the accessories with the engine off and measuring the voltage drop from the post to the clamp.
Its surprising how seldom the appearance of a clamp is different from its connection.
I have seen some that were almost completely white, but had almost no voltage drop, and some nice and shiny ones that were dropping 1.5 volts with about 20 amps of draw.

If things are really strange, I drag out my Fluke Scopemeter and put it on record.

The cool part about using it, especially with a clamp on amp-probe, is that you can see each winding of the starter if your sweep rate is fast enough, and see a possible problem that way, or the way I usually use it, is to slow down the sweep and do a compression test.

As each cylinder compresses, the current goes up. By comparing the height of the spikes, you can see a weak cylinder.
No need to do anything except kill the spark.
30 second compression test!

The winding current test is not as valid, because of the different loads as compression occurs, and would be great if the starter were off the truck and subjected to a constant load.
But, since each winding load occurs once per revolution of the starter, and it is geared down compared to the crank, the compression load changes occur very slowly compared to the windings.

And a dead or shorted winding is real obvious.

 

[BigBen]

OK,

I didn't get everything done that I wanted to this weekend, but now I have an update.

1st: Took the alternator (B) back to the shop and it tested out A-OK on their equipment under load and hot. To cover the wildcard, I had them replace the Voltage Regulator and the Rectifier so I know I'm dealing with all new parts in there.

2nd: Put the alternator (B) back on the truck and measured some resistances. All the ground loops I could measure were at about .2 to .4 ohms with the battery unhooked. (Batt to body/ batt to chassis / chassis to engine / chassis to alternator case / chassis to body)

Next I reconnected everything and fired her up. Initial voltage looks good for charging.

While the truck is running, I put all the load I could find on it. (High beams (4 lights) + 2 KC lights + Blower on high + rear defrost + Radio + dome light + Wipers + CB). Ran to the front and the alternator was keeping the voltage at the battery at 12.9 volts.

Next to measure voltage drops with the engine running and full loading:
Alternator (+) to battery (+) bolt = 0.2 volts.
Battery (-) to Chassis = 0.05 volts
Battery (-) to alternator case (-) = 0.05 volts

On a whim, I checked the alternator (+) to the (+) at the fuse/relay center: 0.66 volts. [These both connect at the Batt (+)

So.... right now it's running well. However, I'm wondering if that 0.66 volts is too high of a drop from the alternator to the fuse/relay center. If you assume that the drop was .2 volts (from above) from the alternator to the battery, I'm losing 0.46 volts from the battery to the fuse/relay center while under load.


I'll actually drive it tomorrow about 50 miles round-trip and I'll see what she does.

Thoughts?

-Ben

 

[Fordum]

Sounds like the problem was the voltage reg and you fixed it.

That .66 voltage drop, is both bad and not too bad.
Ideally, of course you would have no voltage drop, but that would require superconducting cables.
Personally, I would like to see a little less drop than you have.

But, don't forget that you are dealing with 16 year old wiring. And when you build a million cars a year or more, a penny here and a penny there add up. So the wire was probably always marginal.
Plus, the new alt might have higher output than stock.

On top of that, the load you put on it is pretty much the max it should ever see, and pretty unusual.
After all, you maxed out the alt, since it was drawn down to 12.9

This is why, when folks upgrade their alts, they upgrade the wire to the battery also.

And, more importantly, if I remember right, there is a fuse link in that circuit. A fuse link will always drop some voltage, that is how they work......