Altenator

[Blanco_obs]

Okay sooooo I got my truck 2 years ago had huge voltage issues. To find out it’s missing like half the grounds. Added some grounds double check wiring. 1995 Silverado with a 5.7l starts up strong no issues at a good 14v. Drive down the road it lowers to like 13.5. Put a load on and it drops. Yo I say 12. But it will go back up with no loads on. I upgraded my altenator to a 140 amp and the battery is newish. Anyone have a similar issue or heard of one.

 

[Kran]

as alternators heat up they produce less voltage, for non-pcm controlled ones. these trucks are too old to have this pcm controlled.

if the voltage is randomly fluctuating then it could be a couple things. first thing i'd suspect is the alternator regulator going out, which if your 140a unit was installed used or is a non delco brand then that could be the case.

so long as the turn-on wire is on and the battery light is installed and working in the dash there should be no reason for an alt to not work unless there was a power/ground issue (which you seem to have fixed) or the regulator was going out.

have you done the big 3 wiring upgrade? i highly recommend it. it should definitely help boost voltage and lessen voltage drop as the factory wiring is like 8 gauge. 4 gauge or larger (2 or 0) would work great. pure copper OFC or welding cable.

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[RawbDidIt]

Okay sooooo I got my truck 2 years ago had huge voltage issues. To find out it’s missing like half the grounds. Added some grounds double check wiring. 1995 Silverado with a 5.7l starts up strong no issues at a good 14v. Drive down the road it lowers to like 13.5. Put a load on and it drops. Yo I say 12. But it will go back up with no loads on. I upgraded my altenator to a 140 amp and the battery is newish. Anyone have a similar issue or heard of one.

Where are you checking the voltage, at the battery, or the alternator? Please don't tell me your relying on the gage in the dash, that thing is barely better than a dummy light.

If that's what you're getting at the alternator (true voltage reading using an actual multimeter), you've got to add a ground to your engine block, preferably on the alternator mount. You'll also want to change the power wire to the battery, the 6ga stock wire is fine for 110A but if you're actuality using 140A, you need at least 4ga, 1/0ga if you plan on adding anything further on the future. Put a fuse for as close to the rated power of the alternator as possible without going under the rated capacity. Put it as close to the battery as possible.

If you're getting 14+ volts at the alternator, but not the battery, the grounds you added aren't sufficient for the load you're placing on the system.

Adding grounds willy nilly is not the answer, these trucks require 3 good grounds for most applications: fender, frame, and engine block. I run 1500W of sound with these three grounds with no lights dimming, no voltage drop below 14V all day with lights, AC, everything on. I have a 225A alternator and a single battery, but 140A is plenty for stock applications, and enough headroom for a small amp. Make sure your grounds are of the proper gage for the current your pulling. 4ga is perfect for 140A, but if you're looking to add anything in the future, pull the trigger and go 1/0ga now and save yourself the trouble and money of installing the same cables twice. Also recommend installing 4ga for your main power wire that goes from the positive of the battery, over the fan shroud, to the main fuse block. This will improve the reading at the dash, but will not make the gage accurate. To date, I haven't witnessed any owner of this generation of truck stating that their dash gage is as accurate as a multimeter.

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[PlayingWithTBI]

To date, I haven't witnessed any owner of this generation of truck stating that their dash gage is as accurate as a multimeter.

X2 - hell, I have a Dakota Digital dash and it normally reads ~1/2VDC lower than my Fluke meter at the battery! It could be because of smaller gauge wires going to it (I don't have the "Big 3" - yet)? When I turn on all the lights, A/C, fan on high, my dash reads ~13.2 and Fluke stays at 14.2 battery voltage, a full volt difference with an old (somewhere around '05) OE looking alternator.

 

[RawbDidIt]

X2 - hell, I have a Dakota Digital dash and it normally reads ~1/2VDC lower than my Fluke meter at the battery! It could be because of smaller gauge wires going to it (I don't have the "Big 3" - yet)? When I turn on all the lights, A/C, fan on high, my dash reads ~13.2 and Fluke stays at 14.2 battery voltage, a full volt difference with an old (somewhere around '05) OE looking alternator.

For somebody running stock everything, the big three is really just ensuring that the cables aren't corroded to hell. If you add just about anything electrical to these trucks though, it's a big help, but you'll still need more power. the 105-110A alternator that comes with these trucks is just enough to keep the lights and stereo on and the engine firing. You'll get a better reading if you upgrade the ground to the block, but you're going to lose voltage due to the length and gage of the sensor wire on the back of the alternator. Your digital gage actually stands a chance of being accurate if you upgrade that wire and the big 3.

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