Sojer

I have a 87 IROC LB9 and when driving for awhile or idle my volts drop down its only when the car has been runnig for some time. I have a new battery and alt and it still does it. I have checked connetion and its all good my old alt tested good but I changed it any way. The car is not rusty and it haves be doing this sence I got the car 02/14/2011. Sone times the car cuts off and I can't start it till the battery gets enough juice to start. On time it cut off on me while it was a street racing thing goin on bout 150 cars can the cops cam with a flat bed gettin ppl I was able to push my car out the way so they could not see me.

NullHead

Well for starters, I had no idea that kind of race stuff happened around here ... second, check your sense wiring.

Same thing's happening to my brother's 4th gen 1998 camaro, and all I had to do to get 'er going again, was to mess with a custom splice that the previous owner had made, and she started charging again. If the alternator's good, then it's got to be in some other charging system circuit.

Sojer

Yeah french road. Epworth and joy road. Warren and livernoise. Grand river and mcgraw and a ton of other spots its bout 1000 ppl be out on the week end but its winter now so next year would u like to join are car club Motor City Camaro and Firebird Club. We have a meet this Sunday. And wats a sence wie

Aaron_SK

iTrader: (1)

Well, you spelled "and" and "a" correctly.

The sense wire is the larger of the two wires that comes out of the plug going into the alternator (not the large wire on the stud). Depending on year it can connect to the main power feed in the harness, or go to the starter solenoid.

Zerocyde

lol

Mine originally had the sense wire going to the starter wire. After a complete rewiring I went with someone I saw online and just cut it down do about 5 inches and put a ring terminal on it and hooked it up to the main positive stud on the alternator.

Is there anything wrong with that?

Zerocyde

My system NEVER charged correctly in the two years I've had my car until I said SCREW IT and redid the wiring. Here's what I did with the alternator...

Large red wire from the metal stud on the alt: To positive from battery.
Medium red wire from the wire plug on the alt: To the same place as the large red wire from the metal stud.
Small wire marked "L" on the wire plug on the alt: Run this to a light bulb (I used a spare I had for the kick panel light by the drivers foot) and then the other side of the light bulb to a ground.
Any other wires on the wire plug on the alt I just cut off at the clip.

Now it charges like a freaking champ. Hope this helps.

Aaron_SK

iTrader: (1)

So you kids want the alternator class? Okay, here goes:

GM three wire alternators are simple animals. They have one trick the old ones didn't which is that they are internally regulated. The issue with internal regulation is that it needs some sort of feedback to know how much output the car needs.

The fat wire coming off of the stud is the main feed. This needs to go to wherever the battery and fusebox wires come together. On most vehicles (Ford and GM) this is the starter solenoid. If you have aftermarket stuff this location can change.

The medium sized wire coming off of the plug is the sense wire. This wire is hot at all times and tells the alternator what the voltage is at a given point in the harness. The issue is that the voltage is different at different points in the harness.

Think of the sense wire as the "eyes" of the alternator If you hook it up closer to the alternator (as GM often did to save money and simplify the harness) it will chronically undercharge because you have made the sense wire "short-sighted. Likewise if you ran it way off to BFE and tied it in at the back of the car the alternator would chronically overcharge because it would constantly be seeing voltage drop off due to resistance.

Ideally the sense wire should go to the exact same place as the main feed wire that way the alternator will see the voltage dropoff from the battery charging and fusebox accessories, but should not overcharge.

The last, smallest, wire is the trigger wire. This wire turns the regulator on and off. It runs to the ignition switch, but cannot be run directly or it will backfeed through to the coil and the car will not shut off. I you have a stock car hook it up as stock and it will work fine. If you are rebuilding a harness you need to either run it through an alternator light or run a properly rated diode. If you do not connect the trigger wire the alternator will still work... sort of.

The regulator will turn on automatically when it sees a certain RPM (around 1500rpm at the engine IIRC) so the alternator wont actually do anything till you rev the car up. This is how people can get away with those gad-awful one-wire alternators that Summit sells. Start the car, blip the throttle to get it off the choke, alternator comes on. The issue with this is that if you have an EFI car with a stock cam and chip that can start and idle low then the regulator will never turn on and if you just let it sit and idle the battery will eventually die.

Note that many GM 10si and 12si alternators have a second smaller stud directly on the case. This was used as an auxiliary ground and is left alone in most applications.

Also note that all wires must have proper fuses or fusable links and be of a proper gauge.

If you want further reading, here you go:

http://www.madelectrical.com/electrical-tech.shtml

Zerocyde

Cool, thanks.

NullHead

Well my Firebird is currently under construction. I'll accept invitations if someone finds me after my car is running.

Sojer

Sorry for the miss spells on my android and when I text to fast it miss letters. I do have a EFI and I will be going with a miniram. I will have to read this and look at my wires the alt has to come off to look at.
What's IIRC and BFE

Aaron_SK

iTrader: (1)

If I Recall Correctly

Bum F*** Egypt (meaning far away) :P