LB7 Voltage Dip

[OnixMax]

Hey everyone,
Strange issue that I've been battling for a while.. I'll be going down the road, and when I let off the gas, occasionally all my lights dim for 1-2 seconds and the volt meter drops to 11-12 (don't have an exact, just judging by the gauge) and it kicks off things like my heated seats and rear defroster. After that 1-2 seconds, the lights go back to bright and the volt meter goes back up to 14.
Batteries are newish (2013) alternator is new (late 2014).
I don't have any aftermarket anything that would affect the batteries (only aftermarket part is my DSP5 switch).

Any thoughts? At this point I'm kinda stumped. It's not "hurting anything" I suppose, it's just an annoyance at this point.


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[Muff]

Bad alternator

 

[OnixMax]

Alternator is brand new and I've had it tested since..


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[duratothemax]

01-02 or 03-04?

Does the battery light ever come on?

 

[TheBac]

Looks like he has an '03, Ben.

 

[Awenta]

Voltage regulator?

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[DAVe3283]

The 2003+ uses the ECU to control the alternator. It doesn't have a "normal" voltage regulator-- the computer does it all.

I recently put a new alternator on my truck and was having intermittent low voltage issues. Turns out the alternator case was not grounding well to the truck. Fixed that, and all is well!

A quick test if your ground is OK is to turn on all your electric stuff, get a jumper cable, hook the negative up to the battery, and touch the other end of the negative to the alternator frame on bare metal. If you get sparks, you have a ground problem.

 

[OnixMax]

01-02 or 03-04?

Does the battery light ever come on?

03. Battery light never comes on. When my alternator went bad in November, I would get the light and the DIC read 'Battery Not Charging'. Obviously when I swapped alternators, that went away.

 

[OnixMax]

The 2003+ uses the ECU to control the alternator. It doesn't have a "normal" voltage regulator-- the computer does it all.

I recently put a new alternator on my truck and was having intermittent low voltage issues. Turns out the alternator case was not grounding well to the truck. Fixed that, and all is well!

A quick test if your ground is OK is to turn on all your electric stuff, get a jumper cable, hook the negative up to the battery, and touch the other end of the negative to the alternator frame on bare metal. If you get sparks, you have a ground problem.

Interesting - never thought of that. I'll have to try it this weekend and see what I come up with.

It should also be noted that my heated seats no longer work; I think the elements are burned but these issues could be interconnected I suppose. I first started to really notice the voltage drop when it would kick my seats off. I just realized it's kicking the rear defroster off too.

 

[duratothemax]

The 2003+ uses the ECU to control the alternator. It doesn't have a "normal" voltage regulator-- the computer does it all.

No, its still internally regulated by the alternator itself on the Duramax's.

All the ECM does is turn the field on and off. It does not do any regulating.

The alternator reports back to the ECM what duty cycle (% output) it is charging at though, so the ECM can compensate at idle, etc under high electrical load conditions.

 

[DAVe3283]

No, its still internally regulated by the alternator itself on the Duramax's.

All the ECM does is turn the field on and off. It does not do any regulating.

The alternator reports back to the ECM what duty cycle (% output) it is charging at though, so the ECM can compensate at idle, etc under high electrical load conditions.

Oh, yeah, you're right. I've been spending too much time with newer cars.

So in that case, in addition to a poor ground, it is possible the internal regulator is going out (despite the alternator being new). It is probably also worth checking the alternator output cable to the junction block, as if that is loose or corroded, it could cause problems.

 

[THEFERMANATOR]

I'm guessing an aftermarket alternator? Is it a CS-130D, AD230, or AD244? If you go aftermarket there is a chance you got a CS-130D instead of the origanal AD230. In either case, with heated seats, lights, and everything else going, your pushing a 105 amp unit to the limits at idle. I have a AD244 in mine because I didn't want to have my lights dimming with both airs running at idle. You could just be drawing more than your alternator can put out. I have seen aftermarket alternators put out anywhere from 30-70 amps at idle. The engine is going to be drawing around 15-25 amps, lights will be another 10-15, and heated seats could easily push you beyond what the alternator is producing at idle, hence the voltage drop. Once the extra loads kick out, it can produce enough to catch back up.

 

[duratothemax]

I still have the factory original 105 amp alternator on my truck. 230k miles on it, no issues.

If I have the heated seats and defroster and everything on, the only time I notice the lights dimming a bit is during traction control/stability control/ABS activation.

More so than when I had just "ABS only" on my truck...because the TCS/ESC system actually uses two separate pumps, a main ABS pump, and then an auxiliary "booster" pre-charge pump that the system uses to build up pressure much more quickly during TCS/ESC events when the main ABS pump alone cant build pressure fast enough.

So thats heated seats, defroster, lights, and two ABS pumps on my truck. Once the TCS/ESC event is over and the pump(s) shut off, the lights go right back to normal. Never had the voltage drop low enough where the heated seats kick off.

That being said, Ill probably upgrade alternators if/when this 105 amp dies.

 

[duratothemax]

Oh, yeah, you're right. I've been spending too much time with newer cars.

So in that case, in addition to a poor ground, it is possible the internal regulator is going out (despite the alternator being new). It is probably also worth checking the alternator output cable to the junction block, as if that is loose or corroded, it could cause problems.

2005+ half ton trucks and SUV's have "smart" voltage/alternator control.

As far as I know, even on the brand new 2015 HD's, the alternator is still controlled "the old way", with the ECM monitoring regulator duty cycle, and then turning the field on/off depending if the engine is running or not.

 

[duratothemax]

The engine is going to be drawing around 15-25 amps

Are you sure its that much? I would be surprised if its over 10amps.

Yes, the ECM/FICM has to fire the higher-voltage injectors, but its pretty efficient because it captures/"reclaims" the flyback from the injector solenoid closing, and then reuses it to re-charge the cap banks for the next injector event. Pretty clever, and keeps power usage to a minimum.

 

[THEFERMANATOR]

Are you sure its that much? I would be surprised if its over 10amps.

Yes, the ECM/FICM has to fire the higher-voltage injectors, but its pretty efficient because it captures/"reclaims" the flyback from the injector solenoid closing, and then reuses it to re-charge the cap banks for the next injector event. Pretty clever, and keeps power usage to a minimum.

When I checked mine before it was upwards of the 25 amps of current draw for just the truck running. I know my KENNEDy pump doesn't draw that much, but it all adds up REAL quick. I know the single 105 amp wouldn't keep up with my BURB because of the dual airs.

 

[duratothemax]

When I checked mine before it was upwards of the 25 amps of current draw for just the truck running. I know my KENNEDy pump doesn't draw that much, but it all adds up REAL quick. I know the single 105 amp wouldn't keep up with my BURB because of the dual airs.

Is that engine only? Or entire vehicle?

In a stock application, LB7/LLY FICM fuse is 25 amps...and the wire is 14 gauge.

Ive run the entire engine and trans (standalone application) on a single 20-amp fuse, and never had problems.

 

[Awenta]

http://shop.mean-green.com/2006-99-GM-66L-DIESEL-MG8247A.htm

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[THEFERMANATOR]

Is that engine only? Or entire vehicle?

In a stock application, LB7/LLY FICM fuse is 25 amps...and the wire is 14 gauge.

Ive run the entire engine and trans (standalone application) on a single 20-amp fuse, and never had problems.

That was the engine, trans, lift pump, and such. No lights, radio, or air were on.

 

[OnixMax]

I'm guessing an aftermarket alternator? Is it a CS-130D, AD230, or AD244? If you go aftermarket there is a chance you got a CS-130D instead of the origanal AD230. In either case, with heated seats, lights, and everything else going, your pushing a 105 amp unit to the limits at idle. I have a AD244 in mine because I didn't want to have my lights dimming with both airs running at idle. You could just be drawing more than your alternator can put out. I have seen aftermarket alternators put out anywhere from 30-70 amps at idle. The engine is going to be drawing around 15-25 amps, lights will be another 10-15, and heated seats could easily push you beyond what the alternator is producing at idle, hence the voltage drop. Once the extra loads kick out, it can produce enough to catch back up.

Not aftermarket, no. OEM replacement from O'reillys.
I'll check the output cable also.