Austin_Jim

I've read a LOT of threads on various forums about this with out a definitive answer. I'm hoping someone can at least point me in the right direction, or give me some guidance on where to start.

First off, here's the layout:
LS3 and 4L75e from BluePrint Engines with CVF front end accy drive
New American Autowire harness
LED bulbs everywhere (taillights, turn signals, courtesy lights, etc.
Battery to LS ECU - 4ga wire through a circuit breaker
Battery to starter - 1/0ga wire through 250amp fuse
Starter to alternator - 4ga wire
Alternator - one wire, but there is a rectangular plug on it. I believe it is a GM CS130 style

Issue - I was getting a battery drain that would kill the battery in a couple days. I happen to be under the hood the other day and I noticed the alternator was warm and there was a buzz coming from it when the engine was off and the car was cool (was sitting for a while).

Troubleshooting steps:
- Took out fuses one by one, and checked the alternator...still buzzing
- Grounded the alternator with another wire (small gauge though)

Weird thing:
- I accidentally brushed the ground wire across the + wire on the alternator (I know, I know) and the buzzing stopped. WTF?!?!?

Possible things I think I need to try:
- Wire the alternator as a 3 wire (hook up the P L S F wires)
- S to the Batt + at the PCM
- L through resistor to ignition? (this is a question)
- F to GEN wire coming from the ECU (BluePrint uses the GM connect and cruise harness and instructions)? (this is a question)
- Connect a 4ga wire from the alternator to the + on the ECU
- Willing to try anything else

Thanks all,
Jim

wssix99

iTrader: (5)

I would measure voltage between the ground on your battery and the body of the car for a start.

The only thing on the alternator that I would think that could cause a noise are the brushes. Something could be sucking power through the alternator or have a short in such a way that the only path to ground the device can find is backward through the power wire to the alternator. (A problem like this could bypass the fuses if there is a short to a hot battery wire.)

I doubt this is an alternator problem.

Austin_Jim

Voltage is good from battery to body. I forgot to mention the grounds. I have a 1/0ga from battery to frame. 1/0ga from frame to engine. 1/0ga from frame to grounding post in the car where I have everything grounded. Grounds on frame and body were sanded to metal, grounded, then covered with dielectric grease.

wssix99

iTrader: (5)

assume unhooking the battery makes the chattering stop, right? If so, I'd next measure voltage between the power wire on the alternator and the body when the chattering is happening. If you see voltage, then trace it back to the source.

If you don't see voltage, (and the alternator is chattering without power) then I would see an exorcist.

RPM WS6

iTrader: (3)

LOL.

Austin_Jim

I'll schedule the exorcist as a safety measure anyway. However, I'm not sure I understand what you are saying. There is only one wire at the alternator. It is connected to the battery. So I assume there will always be voltage there unless the battery is dead. However, I'm sure I'm not understanding your suggestion.

RPM WS6

iTrader: (3)

Yes, with a one-wire setup there will always be voltage at the alternator. The downside is exactly what you are experiencing (albeit not on the same scale) - battery drain when the vehicle is not in use. I have a 1-wire setup on my '71, but I rarely use the car so I keep the battery disconnected when not in use. Otherwise, it will drain the battery after a couple of weeks (not a couple of days as you are seeing), and there is no buzzing or warmness of the alternator in my case. The quick battery drain might be due to a weak/old battery, but you shouldn't be getting a buzzing sound at the alternator just from applying field voltage full-time (only consequence would be, as mentioned above, quicker than normal battery drain).

So you might need that exorcist after all! Either that, or for some reason it's pulling more power than it should be (hence the buzzing and heat) - like what wssix99 mentioned in post #2 above.

B52bombardier1

I'm thinking one or more bad diodes are blown towards ground in the rectifier portion of the alternator. Get the alternator "load tested" at a well equipped auto parts store and I will bet that it fails the "ripple test" while spinning on the bench at the store.

Rick

wssix99

iTrader: (5)

I was hypothesizing a fault or short in the wire between the alternator and battery, but supposed there could be a problem with the alternator. (That could be the source of heat and this backward flow of power.)

Scratch my comment about measuring voltage to the body. That's not going to prove anything (and a fault in the main cable is going to be unlikely) - but it would be helpful to know if unhooking the battery stops the chatter. Then - if the chatter continues, we think of exorcism. (Disconnecting the battery should indicate if power is flowing backward to the alternator while it is chattering.)


Great point. I can't imagine what else would allow power to flow the wrong way through the part.

jybravo70

iTrader: (5)

I would be more concerned with the heat. In electronics heat is indicating a large power draw or a short (extreme power draw). I would think something inside the alternator is shorting out as pointed out above.

wssix99

iTrader: (5)

Another test to try:
- Disconnect battery after running the car. (I assume this stops the buzzing.)
- Let everything cool.
- Hook up the battery and see if the alternator heats up. (Without starting the car and rotating the engine.)

^ If the alternator heats up on a cool car, this should indicate a bad rectifier.

slothman

what is the battery voltage with the car running? if under 13.8-14.0 you need a new alternator. how old is the unit ??

Austin_Jim

I have read that one wire alternators can drain the battery. But this seems to be a bigger draw (especially with the heat and buzzing). I picked up a PT2145, clipped the CI end (I believe that is the alt designation), ran the sense wire to the battery input on the LS fusebox and the other wire to switched ignition. I'm not super confident that will solve the issue, but it was a inexpensive and easy thing to try. CVF (front end accessory drives on the LS from BluePrint) said that the alternator is a one-wire, but I've gotten incorrect info from them before.

The other thing I'm going to do is run a separate ground to the case of the alternator. An ohm meter shows no resistance from chassis ground to the alternator case. But the FEAD is powder-coated, so it's possible it is grounded, but once things get warm, there is resistance not fully grounding the alt.

If all else fails, I'll try this. Just not super excited to take the alternator out.

I believe if there was a dead short between the alt and battery, my guess is the fuse would blow. I haven't tried disconnection the battery. Do you mean at the battery, or at the alternator?

I'm hoping it's not the alt. Replacing shouldn't be that hard, but it would be nice if I could find something else

I did not exactly do this, but I accidentally hit the ground wire to the BAT terminal on the alternator. This stopped the buzzing and the alternator cooled off and the issue did not occur until I drove the car again

Voltmeter shows ~14v. I finished the car about 3 months or so ago. This is a new alternator that came with the crate engine.

wssix99

iTrader: (5)

It would be good to do a proper disconnect of the battery so you can 100% confirm if electricity is flowing backwards through the alternator. If it is, the alternator needs to come off. The alternator should be a one-way street and the diodes in the rectifier enforce this convention. (You won't be the first person to have a "new" alternator be bad out of the crate/box. You wouldn't be the 1000th, either. Its very common.)

The short of your battery on the positive terminal indicates a bad alternator, but the battery test is a clean way to confirm. (I would have expected your battery to go completely dead if it shorted, right?)

Austin_Jim

Should I disconnect at the battery or at the alternator?

B52bombardier1

At the alternator - it needs to be isolated to test if the drain and alternator heating stops.

Rick

Austin_Jim

I had a chance to take the car out yesterday. Sure enough, the issue came up again. After parking it and turning it off, I let it cool. Once cool, I went out and checked. The alternator was buzzing and warm. I removed the cable from the alternator battery post. The buzzing stopped and it cooled off. I re-connected the cable and still no warmth or buzzing. What does that indicate?

I also though of something else. The cable from my alternator is connected to the starter along with a cable from the battery. Most diagrams I see send the alternator cable to the fuse box. I have a separate cable from the battery to the LS ECU and fusebox. Would that matter? Also, as far as I can tell with a multimeter, the alternator is grounded. Should I attach a separate large ground cable to the alternator? I have 1/0ga grounds from battery to chassis, battery to body, chassis to engine and chassis to grounding post in the passenger compartment for everything in there.

Thanks,
Jim

wssix99

iTrader: (5)

Maybe it is heat related? Does this only happen on long drives? What about short drives? Just running the engine for a minute in your driveway? (For other tests, I would disconnect the battery for convenience and try hooking it back up as the alternator cools down to see if it might be dependent on the temperature of the alternator.)

Austin_Jim

Possible. I haven't tried just starting, then turning it off. Normally when I run it, I head to a show or the store or something like that where it gets up to operating temp.

RPM WS6

iTrader: (3)

Most likely, demonic possession.

At this point, it sounds to me like an internal alternator problem that is excited by operation/heat, and then continues until it's isolated from power. Sounds like disconnecting it effected a 'reset' of some sort. Too bad you don't have another alternator lying around to swap out for a test, that might be all that's needed. Some good test ideas posted by wssix99 above too.