2002 Tahoe e-fans and volt gauge

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.

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.

Fless said:

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.

Click to expand...

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?

88lance said:

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?

Click to expand...

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.

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

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)).

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

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