I have been trying to track down this problem forever. Maybe someone can suggest something for me. I have upgraded 3 wires aka the big 3 (battery + to alt, battery - to frame, battery - to alternator bracket bolt (engine)) with 0 gauge cca wire from KnuKonceptz. I have an ad244 alternator installed from a full size truck, added an inch longer belt so everything fits right and I still seem to get voltage drops when warm. What are you guys thinking? The voltage drops for a few seconds then goes back to normal. This happens when braking and some at idle (mostly when braking or coming to a stop). I have a pair of 55watt aux lights on my brush guard and a 600 watt rms sound system to add to the electrical system plus everything stock. My a/c doesn't work so that stress has been off of the electrical system for some time now. Any ideas? The battery - to alternator bracket bolt should be a fine engine ground right? I'm thinking maybe it's my battery - to frame ground that is acting up. Maybe the frame needs to be cleaned off where that ground bolts down right there.

 

how new is the battery? I would go over all the grounds again and make sure they are good and clean.

 

You're always going to see some voltage drop with these trucks. The voltage is controlled by the PCM with a PWM (pulse with modulated) signal, not the alternator. It's designed not to overcharge the battery when it gets hot (IIRC) so the voltage will always be a little lower than a vehicle with a standard alternator controlled voltage regulator plus the PCM is slow to react when there's a load.

I have a 250A HO alternator in my Jimmy, when it's cold it will be right up a tad over 14v and when hot it's in the 13.5ish neighborhood. Even with LED tail lights the voltage will dip (.5v or so) with the turn signal on. While it's annoying it's just the way the PCM controlled alt works. There's an article HERE that explains it in great detail. However, if I put a solid load on the alternator, like a load tester or jump starting someone, the voltage would dip then come back up and hold there very well with no problems as it should be doing.

There are a few companies that make add on modules that change the PWM signal from the PCM to increase the voltage a little and make the voltage more responsive. The last time I priced one it was about $150.

 

On 1998 and older, voltage was controlled by a regulator inside the alternator. The 1999 and newer PWM systems can be easily converted back to the old way of doing it.

 

I think the alt came out of an '01 'Burban but I could be wrong. Are you referencing GM trucks or just the S-Series?

 

1999 & newer S & T series use PWM to control the alternator.
2000 & newer C & K series use PWM.

 

I had/have the same problem, I have own my 2000 LT 4x4 Blazer since 2002 and I pretty much know how it runs. My always ran around 14.2 on the vote meter inside the SUV until about a year ago it started dropping to 3.8 or so and the meter would move when the turn sigs were on. I would be showing 14.2 hit the turn sig and down to 13.8 and not recover back to 14.2. I have this friend on mine who has his own shop so I took it there and left it for two weeks he said he couldn't anything wrong, he even change the dash out. Now keep in mind that I just replace the battery and alt so they were good. So I bought it back home and was doing the I dare you stare while it was running. Now in the mean time I brought a new volt meter I could hook up under the hook and ran it straight from the battery and show 14.0 while running and not 13.8...so I was crusing e-bay and saw this neat little thing that you plug into your cig lighter and it will show you the votage...So I plug that in, it show 14.2 at the beginning and drive and hit the turn sig and votage drops on the thing in cig lighter and inside volt meter...Now I and my mech went through every thing and test and clean each ground. Then one day I was giving it the stare as it was running and more the ground battery cable and it spark a little, I said what? I check my meter inside both of them, one show 14.5 then settle at 14.2 and the one in the dash about the same...So I said I got it ground battery cable, so I went an got me a new one and put it on, wal-la..every thing back to normal until a few days ago and back again to votage drop...I think its about time to get rid of this headache...All I can do is all I can do....

 

Sorry about the bad grammer..I read it today and said ugh is that terrible.....

 

For those who are having voltage drop issues with these chevy's, I have had all the these same problems. Try this salution and If needed I will explain. Remove the throttle body and clean all the carbon out of it, remove the TPS clean also there is an o-ring behind it don't loose it. Remove the IAC either clean it purchase a new one, I just died to replace it. After cleaning everything reassemble, insure you have a fully charged battery. Attempt to start it, it may run at a high rpm but that's okay, after about one minuteshut the vehicle off remove the battery terminals for about a minute then reconnect, vehicle should run at a normal idle. Take it out for a drive and see how it runs.

 

Voltage drop is an electrical problem. Cleaning the TPS, IAC, and the throttle body, all affect engine performance, and have nothing to do with voltage drop. Disconnecting and reconnecting the battery does not reset, relearn, or clear any memories in the PCM. It will however, cause the radio presets to be lost, and the clock will need to be manually reset. If it does make a difference with voltage drop, the cable connections probably need attention