2002 Tahoe e-fans and volt gauge

[88lance]

Seen several posts about volt gauge bouncing around, but my situation seems a bit different since I just changed to electric fans, which is when it started.

So, '02 Z71 Tahoe, volt gauge always sits at 14 and never seems to move. I added electric fans and got rid of the clutch fan, and now when the fans kick on, the volt gauge bounces between 13-15 volts very quickly while the fans are on. When the fans clicks off, it stops at 14 and sits steady again.

At night you can actually see the fluctuations in the headlights and dash lights.

I have read that the alternator going bad is usually the cause for this, but since there was nothing wrong with the alternator before I added the fans, it makes me think it has something more to do with the fans causing the fluctuations, rather than something coincidentally going out right when I added the fans.

Anyone know what causes this?

 

[justirv]

Seen several posts about volt gauge bouncing around, but my situation seems a bit different since I just changed to electric fans, which is when it started.

So, '02 Z71 Tahoe, volt gauge always sits at 14 and never seems to move. I added electric fans and got rid of the clutch fan, and now when the fans kick on, the volt gauge bounces between 13-15 volts very quickly while the fans are on. When the fans clicks off, it stops at 14 and sits steady again.

At night you can actually see the fluctuations in the headlights and dash lights.

I have read that the alternator going bad is usually the cause for this, but since there was nothing wrong with the alternator before I added the fans, it makes me think it has something more to do with the fans causing the fluctuations, rather than something coincidentally going out right when I added the fans.

Anyone know what causes this?

Take a look at your RPO codes in the glovebox. I believe the '02's with fan clutch came with a 105 amp alternator. When they transitioned to e-fans in '05, the alternator got bumped up to 130 amp. This could explain the voltage drop or "instability ". Can I ask what e-fan harness you used, is it '05 OEM or 3rd party (like Nelson, etc.). I ask to see how you connected the AC fan on command, by tapping into the AC clutch signal, or adding a pin for ECU control?

 

[88lance]

Take a look at your RPO codes in the glovebox. I believe the '02's with fan clutch came with a 105 amp alternator. When they transitioned to e-fans in '05, the alternator got bumped up to 130 amp. This could explain the voltage drop or "instability ". Can I ask what e-fan harness you used, is it '05 OEM or 3rd party (like Nelson, etc.). I ask to see how you connected the AC fan on command, by tapping into the AC clutch signal, or adding a pin for ECU control?

Thanks for the reply. Fans and harness are from an '05. I tapped into the clutch signal wire under the fuse box.

I thought all the Z-71's were the larger alternator, I didn't know they didn't do the upgrade until '05, that may be my issue then.

I'll check my code in the glovebox this evening also.

 

[88lance]

 

[Fless]

Yours is KG8 so 130A, unless it's been changed. It's usually engraved into the housing on an OE alternator.

K68 = 105a
KG3 = 145a
KG8 = 130a

 

[88lance]

Yours is KG8 so 130A, unless it's been changed. It's usually engraved into the housing on an OE alternator.

K68 = 105a
KG3 = 145a
KG8 = 130a

I don't see an engraving, but it does say remanufactured for AC Delco

 

[Marky Dissod]

Your alternator is a KG8 = 130A.
Next time you go to buy an alternator, LIE.
Tell them you have a KG3 or KG4, so you'll get a stronger alternator.
I upgraded to a KG3, and will not settle for a KG8 again.
Next time I'll try for a KG4.

 

[88lance]

Your alternator is a KG8 = 130A.
Next time you go to buy an alternator, LIE.
Tell them you have a KG3 or KG4, so you'll get a stronger alternator.
I upgraded to a KG3, and will not settle for a KG8 again.
Next time I'll try for a KG4.

Could this fix the voltage fluctuation issue? Is the KG4 higher amp than the KG-3, or just better in other ways but still 145 a?

 

[Marky Dissod]

Could this fix the voltage fluctuation issue?
Is the KG4 higher amp than the KG3, or just better in other ways but still 145A?

Two part answer.
Part 1. KG8 = 130A
KG3 = 140A
KG4 = 150A

If the alternator's connector, connects to the new alternator, you're good to go.

2. Every GM vehicle I've ever owned got a pcm tune.
One of the MANY things I get addressed, is turning up the idle from ≈500RpM, to about 600RPM.
In and of itself, that kept even my KG8 alternator from dozing off - but I upgraded anyway.

Also note I did the electrical fans upgrade. Also note your next mods in my sig.

 

[88lance]

Two part answer.
Part 1. KG8 = 130A
KG3 = 140A
KG4 = 150A

If the alternator's connector, connects to the new alternator, you're good to go.

2. Every GM vehicle I've ever owned got a pcm tune.
One of the MANY things I get addressed, is turning up the idle from ≈500RpM, to about 600RPM.
In and of itself, that kept even my KG8 alternator from dozing off - but I upgraded anyway.

Also note I did the electrical fans upgrade. Also note your next mods in my sig.

I don't think increasing the idle would fix my issue on this one, I should have mentioned it does it even at highway speeds, so running 2,000 rpm it is still bouncing rapidly.

 

[Marky Dissod]

One of the OTHER many things altered in the tune is as follows:
When the electrical fans kick on, they can kick on LOW speed, or HIGH speed. (Older vehicles would be one fan=LOW, or both=HIGH.)
If the AC psi is high enough, both electrical fans can go from off to HIGH in under a second.
That instantaneous current draw could be the cause of your symptoms, especially over 30MpH.

Over 30MpH, HIGH should be completely unnecessary.
My pcm tune does not allow HIGH over 30MpH, so I've never experienced your symptoms.

 

[Fless]

The alternator shown is a 130A unit based on the part number (19244745).

EDIT: you could have some issues with compromised battery cables and grounds, and may want to consider replacing some of them and doing the "big 3." You could also test for voltage drop between the + and - battery connections and the engine block and body.

 

[88lance]

The alternator shown is a 130A unit based on the part number (19244745).

EDIT: you could have some issues with compromised battery cables and grounds, and may want to consider replacing some of them and doing the "big 3." You could also test for voltage drop between the + and - battery connections and the engine block and body.

I don't really know what the big 3 is, can you explain?
So I need to put a volt meter at each end of the cables and see if they are fluctuating also?

 

[justirv]

I don't really know what the big 3 is, can you explain?
So I need to put a volt meter at each end of the cables and see if they are fluctuating also?

The "Big 3" is a grounding upgrade strategy to address grounding issues. Do a search on that, I don't have a link readily available. Highly recommended as the old ground straps were marginally sized, and by now may have significant internal corrosion, impacting conductivity.

 

[Fless]

Voltage drop is done while an appropriate load is applied to the circuit. Eric O shows how:

 

[adriver]

The big 3 is 3 bigger cables off the battery. It's going to make your voltage drop worse, until you up your power supplied.

The Efans are causing the voltage drop. The 05-07 efans are IIRC 5 and 7 blade fans. Those are 350w motors. So When those kick on they are causing a (350w/ 14.4v =) 24 amp draw. The HD fans and later fans that were, (i forget, 7/7? blades? that have more blades to be quieter) are (500w motors, 500w/ 14.4v = ) 34.7 amp draw when they kick on.

If you are on a stock alt, that's a decent draw to cause a small voltage drop. When they started adding efans from factory, they bumped up the alts about 30 amps. Your alternator puts out the least at idle, so that is where you would notice it most. Then if you have other draws going, EFI, and ECU are kind of required. Lights, hazards, brake lights, AC, radio, window motors being used will cause a larger draw as well.

If that's me, I'm going to test for a drop at idle, and you shouldn't have Efans kick on when at driving speeds, (yeah, I've noticed above about 30, when you get enough airflow just driving you don't even need fans). You could test by putting on headlights, radio at high volume, using your windows, and turning your AC on at highway speeds. I'm sure it's doing 130 amps at 2000/2500 rpm, but it's probably doing 50-60(??) at idle.

The voltage drop isn't going to hurt anything. I personally, would look for another reason to go bigger, (amplifiers, or wait till it goes out). I know autozone offers a 160 amp for your small case. If it's happening at idle, then a cheap alt is going to make it worse, (even if it puts out more amps (at full output)).

 

[Marky Dissod]

Everything @adriver just said above, plus also, turn up your idle from under 520RpM to over 620RpM.

 

[88lance]

What confused me was that it is doing this at highway speeds, at idle it barely even does it. When I get up to 2k RPM's driving down the highway, that's when the needle is rapidly bouncing