Voltage fluctuation/charging issue (NOT GRID HEATER)

[JB&S]

For some time (roughly two years), voltage quickly fluctuates anywhere from 13. 1 to 15. 2 volts at idle. It usually stabilizes somewhat when driving to around 14. 6 or 14. 7 volts. This happens year-round and I live in Arkansas. It causes my lights (interior and headlights) to flicker and also causes my FASS titanium 95 pump to surge and fluctuate as well. I replaced both batteries back in February (the originals were six years old and sluggish) with O'reilly AGM batteries. The problem persisted. I checked all the grounds and battery cables for tightness/corrosion, etc. I am wondering if the original alternator is on its way out? Or could there be something else I need to check? Any ideas would be greatly appreciated.



Thanks,



-Josh

 

[cerberusiam]

How do you know it is not the grid heater?

 

[SierraRam]

Sounds like the heater to me. You won't see the dash icon come on but the grid heater continues to cycle.

 

[JB&S]

What I meant by that is it's not the grid heater cycling on and off. It does this year-round (even when it's 100 degrees). It is a separate voltage fluctuation from the grid heater cycling. It's very erractic jumping from 13. 1 or so to 15. 2 (it varies) very quickly.

 

[chipster]

What I meant by that is it's not the grid heater cycling on and off. It does this year-round (even when it's 100 degrees). It is a separate voltage fluctuation from the grid heater cycling. It's very erractic jumping from 13. 1 or so to 15. 2 (it varies) very quickly.

there could be a malfunction in the grid control system. easy way to check is to unhook the grid solenoids, and drive the truck. if the voltage stays steady, there`s a problem in the controll circuit, if it still varies, the problem is else where. it pays to check the obvious no matter how much you THINK it is not the problem.

 

[JJPage]

I can hear my grid heater relay actuating behind the passenger side dash quite prominently, would be no need to unhook the solenoids to isolate.

 

[Prairie Dog]

I had the same symptom (caused by batteries in my case) and could see the rhythmic voltage surging the OP speaks of. It's very obvious when this sort of thing happens because it also happens while the grids are cycling. Anyone who has driven a CTD for a length of time knows the idiosyncrasies of how the grids work. BTW, load testing didn't reveal any problems with the batts and all terminations were clean.
So when the OP says it's not the grids, I'm going to give him credit for knowing what he's talking about and believe him.

I have no idea what in my battery's caused this problem but some characteristic was causing the computer to have fits.
I know you said you cleaned the grounds but did you check the ones around the qrtr panels of the eng compartment? If not then I suggest cleaning these up as well. They're important (one is ECM negative supply voltage) and tend to get rusty and contaminated.

The ground terminal in the 3:00 position in this pic is the ECM ground - might start with that one plus you can see another at about the 9:00 position.

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[cerberusiam]

If the relays are sticking you won't hear them activate. They will draw current until they warm enough release, when they don't then lots of smoke under the hood.

Disconnect the power to the relays and the ECU harness validate there is NOT an issue in the relays would be a good start.

Battery temp sensor under the driver side battery will also cause some very weird readings and charging characterisitcs.

 

[JB&S]

Fellas, I appreciate all of the input! I will recheck the grounds (thanks prairie dog) and check driver side batt temp sensor (thanks cerberusiam). The reason I specified that it was not the grid heater cycling is because it seems like every week there is a new post from a newbie about "Why does my voltage drop really low when its cold then recover and it does it several times?" LOL!!! I was just trying to avoid another one of those posts. I read the volts from my Edge insight. Although its digital, if you could imagine a quality gauge with a needle, it would be bouncing from those numbers around (13. 2 to 15. 2) very quickly. Imagine wagging your finger back and forth quickly HAHA!!!
Thanks again,
-Josh

 

[cerberusiam]

I read the volts from my Edge insight.

And that may be the root of the problem. The CTS is reading off the bus and that is only setting what the ECU wants you to see. If you are not checking voltage at the alternator and drive side battery you will miss a multitude of issues. You NEED to verify at the alternator and driver side battery the fluctuation is real.

The ECU regulates charge off the battery temp sensor and its own unknown algorithms. What is actually happening at the batteries is not what you may see on the gauge or on the bus becuase it is not a real reading. The CAN systems are known for these false readings and bugs in the ECU that will cause all kinds of misdirection. The 06's are the worst year for these problems. It would not be unusual if you have a ECU problem that is causing it.

 

[JB&S]

Just looked over driver side battery connections. The terminal connectors were tight as I had checked earlier. The lock nut for the positive cable running to the passenger battery (which also has my FASS pos power wire) was a hair loose. I could move the cables ever so slightly. Tightened up and surprise surprise voltage fluctation ceased. To test, I backed it off to about where it was and the fluctuation started again. DOH!!!! Sometimes it's the small things that get overlooked... MY BAD!! Haha!! Hope everyone has a great weekend.

-Josh

 

[Prairie Dog]

Bizarre! Thanks for the update.