I've read quite a few threads on here about guys having charging problems. I have had issues as well, and thought I would share my findings.

I had a Duralast Gold reman alternator (fresh) that would charge 14.0 V (at the battery terminals) at idle at initial cold start-up. As things warmed up, voltage would drop to 13V. If the fans kicked on, I'd see mid 12's. Something was not right.

I have heard that the ECM controls alternator output, so to rule the ECM out as the problem (and to see if it actually controls voltage), I ran a wire to the L terminal on the alternator through a 470 ohm resistor straight to the battery. This had ZERO effect, and the voltage acted as if I had the stock wiring plugged in.

I decided then to open up the "New" alternator to see what was going on inside. I found a stock, old GM voltage regulator with a green paint dot on it! My guess is that the reman guy ran a diagnostic test on it when it was cold, and it passed, so they stuck it back in. I then went to Advance Auto and bought a new BWD voltage regulator (R926) and brush set. After installing these parts, I got 14.3 volts at the battery at idle, irregardless of load! A $30 voltage regulator solved all of these problems!

I then decided to check all of the 12V+ and ground connections under the hood. I disassebled the ground stud, cleaned, and placed dielectric grease on all of the terminals, and then added an additional 8 ga wire from the stud to the ground terminal on the battery (with an add-on side-terminal screw). This increased battery voltage to 14.5V. I then did the same thing to the positive distribution block on the fender. I also added an 8 ga wire from the block to the positive side of the battery, and another from the alternator output to the positive terminal. This gave me 14.7V at the battery!

So to sum things up:

1. Cleaning and greasing power and ground connections can reduce voltage drop.
2. Factory battery cables are undersized.
3. GM voltage regulators can fail with age.
4. The ECM does not control voltage output.

Hopefully this info will help anyone with charging problems!

 

Good to know I will be looking into this as I replace my alternator soon. Mine being a 93 as well I had the wimpy 120 amp and am upgrading it to a 95 140 amp. Was this test done on a stock amp alternator or did you upgrade too?

 

Big 3 wire mod is the best bang for your buck in the electronics dept for your car.

 

What's involved with this mod? I did upgrade all my wiring all ready to 0 gauge. My alt just took a crap on me the other day,now she's down again lol.. anything else I would need to upgrade?

 

hmmm.. interesting.. i think i'll pull mine off and check this, i've had voltage issues forever, always starts strong and loses about 2 volts as it warms up

 

Mine has a 1/0 starter cable, 2 gauge for alternator and junction box. 1/0 gauge engine ground and 2 gauge body ground

 

All of this was done on the stock 93 120 Amp alternator. I wouldn't say it's wimpy either, when it's actually working correctly. Voltage does not drop when load is applied at idle. This of course means the alternator is cranking out the amperage that it should.

You might want to try replacing the voltage regulator in yours before you buy a new one. If you do, be sure to order a brush and holder kit, since you will probably break the one that's in there now when you take it apart (happened to me).

 

Cool sounds good I will do this as soon as the funds let me LOL... I was reading your sig how do you like the moates apu1? I was going to go this route but am a newbie as far as tuning. I have a good friend that tunes alot of lsx cars and hopefully he can tune with it. what program did you use?

 

The APU1 is awesome! The only thing that doesn't work well is the realtime emulator. The 93 ECM just doesn't like on the fly changes. Other than that, it's incredible. I have mine permanently mounted behind the passenger kick-panel. I just plug in my laptop via USB and I'm good to go. I'd highly recommend it.

I use TunerCat to modify the actual .bin file, and TunerPro RT (which comes in the APU1 package) to talk to the APU1 box and to datalog.

 

What's the 3 wire mod?

 

what color green is it? opened mine up today and it has a neon green dot on it. i just had it rebuilt, the voltage regulator looks new though?

i have another alternator so i opened that one up and no dot on it.

 

switched from my rebuilt alternator, with the neon green dot, that was giving me ~11-12volts

to the "unkown condition" one that looks like it came off of the titanic and now it doesn't go below 14 volts. **** yeah!!

 

Another 'rebuilt' old alternator! I guess the voltage regulators check out fine when they're cold, but problems arise when heat is introduced. Glad you got yours straight!

 

yeah my rebuilt one would start about 13.8-14v then after about two miles it would be down to 11-12volts...


its been driving me crazy for like a year and a half! so glad i saw this thread! thanks man!

 

I am having the same symptoms, Good when cold then after some driving it drops drastically. Sometimes as low as 10v. I will definitely look into replacing that regulator. My alternator is a re-man and looks like everything is new in it but I guess you never know these days. Thanks for posting up!

 

wow, i had this problem, but just dismissed it... i guess i need to replace mine too, thanks!!

 

what's the 3 wire mod? what wire size?

1- pos from batt to alt, 8ga min.
2- neg from batt to ground, 8 ga min.
3- ???

is the third from batt to starter or to fuel pump?

 

Alt to the junction box would be my guess