Chevy & GMC Vans

Noticed my gauge reading 11-11.5, when I was parking it last night, gave it some gas and my headlights got a little brighter and the needle went up a bit, went in to restaurant for dinner with wifey, came back out, it started right up, but remained at same low voltage. On the freeway ride home, it stayed at 14 the whole way, at stoplights, down to about 11. Parked it overnight, started it this morning and the gauge read 14.5-15, until it warmed up, then back to about 11, I might be crazy and listening too hard, but I think I hear a new whirring type noise from the engine. I checked the battery cable connections and they were tight, shiny, bright and new with zero corrosion. I'm guessing bad ground somewhere or alternator and was wondering what's the best way to attack this? Also, I recently upgraded sealed beam headlights to composite style, all I really did wiring wise is add an extra ground to each composite plug, and I made sure to make good weatherproof connections, and it's also been raining like a mofo where I'm at and I have gone through some real nice mini-lakes at speed, due to all the flooding recently.

To start with, these gauges aren't very accurate. The normal output of a stock alternator is 13.6 - 14.2. Check your system with a digital volt meter. That will give you a better reading. From your description I'd say everything is normal. If it isn't you'll find out at a most inconvenient time.

I have had almost the same problem on 2 of my vans and with in 2 months each time the alternator died. I would start looking for a good price on a new Alt because I think you will be swapping one out in your near future.

Hey Slim,
Checking your battery connection is a good start, but make sure you check the other ends too.
Check inside the connectors by cutting the insulation back a little bit. Although the connection may look good, corrosion can occure inside the crimp-on connector.
If you have any doubt replace your "big three" with new wires.

Peter

Checked things with voltmeter
Engine off, batt: ~12.62 it's only 3 months old
engine on, at start: ~14.59
after engine on & warm with DRL: ~13.15
engine on warmed with lights and heater on low: ~12.70
engine on warmed with highbeams on and heater on high: ~12.25
are these acceptable numbers? If I'm not mistaken the intrument panel gauge was always pegged at 14 no matter what was on, now it reads at about 11 after warm and goes to 14 only while driving, and I still think there is a new low volume high pitched whirr sound coming from the engine, is my only choice to pull the alternator and have it checked?

Kidhauler wrote:I have had almost the same problem on 2 of my vans and with in 2 months each time the alternator died. I would start looking for a good price on a new Alt because I think you will be swapping one out in your near future.

+1

My alternator was making a whining noise and putting out 10 volts or less at idle (which means it really wasn't putting out anything, just running on the battery), and then over 15.5 at cruise! I was measuring my voltage with a Fluke 88V meter. A new alternator fixed it.

On the back of your alternator you will find a small hole.
Inside that hole is a metal tab.
Connect your volt meter to your battery and start your engine.
Carefully, take a screwdriver and short out that tab to the body of the alternator just long enough to get a reading on your meter. A second or two is all you will need to get a reading!!!
If your alternator is charging you will see a voltage spike of 18 volts or more on your meter.
If you do not see a substantial spike in voltage then your alternator is not working properly.
Do not hold the screw driver there for any longer than you have to, as by doing this you are bypassing the voltage regulator and you can cause damage to your battery and electrical system if you hold it on there for to long.
If your not comfortable doing this then by all meens take it to a parts store an have them check it. It's usually a free service.
Peter

ps; Have you checked your belt tensioner?

Kidhauler wrote:I have had almost the same problem on 2 of my vans and with in 2 months each time the alternator died. I would start looking for a good price on a new Alt because I think you will be swapping one out in your near future.

+2
i've gone through 3 alternator in a year and a half period 2 of which whined before they kicked the bucket and showed the same symptoms you describe in your first post

I definitely will do the ground tab test, just read that in chilton's, they stated 15 or higher. Looks like I will be parking it until I can fix the issue. I was already planning on upgrading the big 3 right before this happened, just haven't been able to source some welding cable, tried home depot, since I was already there for some lumber, but it was a no go. I also need to replace the tensioner, it chirps intermittenly and hops around more than I like, might as well do the idler pulley since I'll be in there, I also have a throttle plate I modded to remove the restrictor that I'd like to get in there too. Next on the list is drivers side lock actuator which recently stopped working. Looks like the trans cooler I wanted to install will have to wait a bit, as will the overlands lift and rims/tires

If you replace your tensioner it might just be, problem solved. A weak or stuck tensioner can create the noise you described and cause your alternator to not work to it's optimum.

That would be just too easy if it was just the tensioner, I hope it's the culprit seeing as the alternator only has 40k on it, the van is new to me but I'm assuming it sat around a bit for the past 11yrs, I've been driving it nonstop until now since I acquired it, and other than this issue it drives as a new vehicle

Well, sometimes it's the simple things.

My manual lists 2 types of alternators used in the Astro, an SI type with grounding tab hole, and newer CS type with no grounding tab hole. Anybody know placement of the grounding tab hole? It's not in the spot that the Chilton manual drawing shows, I did find a small through hole with what appears to have copper inside the base of the hole, in the upper left backside of the alternator, would this be it? Also, do you guys have any tips on how to do this test with 1 person? My meter won't reach inside the cab, maybe see if I can set it on the windshield facing me?

Ok so I just figured out by reading more of the manual that to tell the difference between the 2 types of alternators is that the SI type uses bolts to fasten the two halves of the alternator together, and the CS type uses rivets to fasten the two halves together, I have confirmed that I have the SI type alternator, so where is that dang ground hole supposed to be? I'm stumped

Had the alternator tested at a shop and results came back as charging system malfunction, excess ripple detected. I think that translates to bad stator or diodes, also with some google research on that diagnosis, it said to check alternator bracket and belts, which I did and threw on a new tensioner which it needed anyways, and a new idler pulley, started it up and van seems to run quieter and idle smoother, but after warmup the volts dipped low again, so it appears that I am now in the market for new alternator, at a local shop I can get a no-name 100 amp lifetime warranty alt for about $100, or AC Delco reman. 105amp with no warranty for about $250, seems a bit high to me? My current alt is a Delphi 105 amp and I'd like to find another one AC or Delphi for around $200, is that a decent price for these units?