Fluctuating voltage

[Adventuren1]

My voltage has started to fluctuate wildly. The gauge drops to about 10 volts but just guessing on that. I can hear a click in the engine when the voltage drops. It cycles like that for awhile then stops. I cleaned the battery connections and the batteries tested ok recently. Is this a voltage regulator issue or alternator issue? 2007 5.9 2500

Thanks for any input

 

[DavidC]

Grid Heater most likely which is normal. What are the outside temps ?

 

[AH64ID]

Sounds like normal winter operation on older batteries if it’s really getting to 10. Has the truck been sitting a while?

The click is the grid heater relay for the post-start heat cycle.

100% normal to go from 14 to 11 during the grid heater cycle.

 

[Adventuren1]

I'm in the PNW so it's not cold at all, usually about 40 in the mornings. The truck is a daily driver. And it does this even when the engine is hot

 

[Adventuren1]

It dims the headlights to where they barely work. This can't be normal. Plus it's a new issue. I should have made that clearer, sorry.

 

[GCroyle]

How many miles on alternator?

 

[AH64ID]

The post-start heat cycle works below 66° and does it even on a warm engine. It’s mainly for emissions at the warmer temps.

Dimming of the headlights is also normal, but if you’re seeing it more noticeable now that previously I would suspect either the batteries are weak or the alternator is weak, or both. Weak batteries can overwork the alternator and both need replaced.

How old are the batteries?

Any new electrical mods to the truck that may have more of a parasitic draw than you’ve had in the past?

 

[DavidC]

You could disconnect the grid power, the large wires not the contactor coil (the small wire) and see if that clears it. I do not know all the sensors that trigger those but others will on here. 40 degrees will trigger the grids i think it is actually in the 60 range but I may be wrong. If you disconnect the coil wire I understand it could set a check engine light.

 

[Adventuren1]

How many miles on alternator?

260K on the truck. I have a good meter but I'm clueless how to use it. I'm going to the shop soon to get the crank and cam shaft position sensors changed again so I can have it checked then. Was just hoping to learn something about the issue before I go pay to have it diagnosed

 

[Adventuren1]

You could disconnect the grid power, the large wires not the contactor coil (the small wire) and see if that clears it. I do not know all the sensors that trigger those but others will on here. 40 degrees will trigger the grids i think it is actually in the 60 range but I may be wrong. If you disconnect the coil wire I understand it could set a check engine light.

Thanks. I'll look into the grid heater. But I just spent 2 years in San Diego and it did this down there too. And it's always 70 and sunny in San Diego I miss flip flops and shorts every day.

 

[DavidC]

With that mileage you may need to rebuild the alternator or replace.

 

[GCroyle]

A sat afternoon SWAG.

If you can pull alternator and remove brush assy. Look at brushes, worn? Now look at slip ring. is one of them black vs brass looking? Black might be worn down past slip ring conductor and into the nylon/plastic. It's a "unique" slip ring repair procedure if i'm anywhere near close on couch diagnostics.

Again, big SWAG but that's what heppened to my 2005 at about 210K or so. It even tested good but not when it was in truck. ORL reman still cranking it out for me.

 

[seafish]

Need more info here ...How OLD are the batteries??

If you have already checked the condition of the wires and connections, as well as properly cleaned and tightened the trucks battery terminals , then likely the batteries are going bad despite "testing" good.

In short, the grid heaters operation puts an inordinate amount of load on the batteries and even ones that tests "good" (but on the low side of good with a computerized tester) might not provide enough current to run the truck accessories while the grid heaters are operating.

IMO, the ONLY way to properly test a battery is with a battery hygrometer that reads the internal condition of each individual battery cell coupled with a properly used load tester.

That said, if you know what you are doing electrically speaking, feel free to disconnect the grid heater wires (only from the relay side of them) and that should temporarily solve your headlight dimming problem ... until the batteries fail completely.

Of course, like others are saying, it could also be your alternator going bad, but I'd start with the batteries,

Just my .02

 

[DavidC]

I have read a lot of threads on our alternators and the general consensus is the grid heaters (200amp draw) is what kills them. You could very well have some diodes bad in the alternator which does not allow enough power to charge the batteries or help compensate for loads.

 

[AH64ID]

The grids aren't as hard on the batteries as believed, but combine the grids with weak batteries and you will eat the brushes/slip ring FAST! Grids cycle their load so there isn't as much heat buildup, but low batteries take constant peak power and the heat wears the alternator out fast.

 

[Tuesdak]

But I just spent 2 years in San Diego

Your batteries are TOAST!!! It's hard to wrap one's head around extreme short life of batteries in heat. In hotter areas of the country we have a simple test for batteries:

Are they under 2 years old?

Yes: Well at least it's under warranty if it tests bad or fails.

NO, over two years old. Replace them. Anyone running longer that 2 years is simply pressing their luck. And congrats they actually made it two years.

You have to take the ground off one of the batteries to test them. Most stores don't and with one good battery and one 'open' or weak battery the test passes. The good battery carries the bad battery through the test.

Again insane life reduction for higher average heat.

https://lifelinebatteries.com/knowledge-center/

Battery calendar and cycle life are also affected by temperature. As a rule of thumb, the battery life decreases by 50% for every 10⁰C rise in temperature. Thus, a battery that lasts 6 years at 25⁰C will last 3 years at 35⁰C, 1.5 years at 45⁰C, and 0.75 years at 55⁰C. Similarly, a battery that lasts 1000 cycles at 25⁰C will last 500 cycles at 35⁰C, 250 cycles at 45⁰C, and 125 cycles at 55⁰C

 

[Wayne M.]

260K on the truck. I have a good meter but I'm clueless how to use it. I'm going to the shop soon to get the crank and cam shaft position sensors changed again so I can have it checked then. Was just hoping to learn something about the issue before I go pay to have it diagnosed

Why are you changing the cam & crank pos sensors *again*?
This is a tricky one to diagnose but for sure, eliminate the obvious first. Isolate the batteries and determine the health. The battery cross over cable can cause a run around, and is tough to check.

 

[Adventuren1]

View attachment 126565
A sat afternoon SWAG.

If you can pull alternator and remove brush assy. Look at brushes, worn? Now look at slip ring. is one of them black vs brass looking? Black might be worn down past slip ring conductor and into the nylon/plastic. It's a "unique" slip ring repair procedure if i'm anywhere near close on couch diagnostics.

Again, big SWAG but that's what heppened to my 2005 at about 210K or so. It even tested good but not when it was in truck. ORL reman still cranking it out for me.

Great info! Thank you. I'll try that.

 

[DavidC]

Before you tear things apart
https://axleaddict.com/auto-repair/Alternator-Problems-and-Automotive-Charging-System-Tests

 

[Adventuren1]

Why are you changing the cam & crank pos sensors *again*?
This is a tricky one to diagnose but for sure, eliminate the obvious first. Isolate the batteries and determine the health. The battery cross over cable can cause a run around, and is tough to check.

Those sensors are going bad for the second time. They start to cause a miss in the engine and pretty soon it won't run. And sounds horrible when those sensors go bad. It's shut and tow right then.