kameleon25

I have double checked the voltage at the 3 pin plug. There is 1 that is constantly powered and the other 2 go on/off with the ignition. I have tried multiple grounds and still no go. I am about to see if running a new wire from alternator to battery will do it.

kameleon25

Being that I am getting voltage to the alternator 3pin plug it is probably not the fusible links. Since they would kill voltage to that plug in the diagram you showed, at least the way I look at it it would. I was thinking it might be the terminals in the plug not connecting but I'm wondering if it is the alternator. It tests fine on the bench but won't work on the car. An I missing something?

Mr Jokster

iTrader: (8)

I wish I were there, I'd figure it out rather quickly. I hate this internet crap LoL

Question, have you checked the output right at the power nipple of the alternator while the car is on? (The wire that goes to the fuse box) Not AT the fuse box, right at the nipple. Does it read ~14.4v?

kameleon25

My brother who is a mechanic at a local dealership came by to help me today. We checked everything. Continuity to everything, even traced down the wire to the ECU (which I had no idea it was under the hood! I found out after u dismantled the interior). Everything checked out. Only thing I can think is the voltage regulator in the alternator is bad. Even though it tests fine on the bench at the local Oreilly. So with that I'm going to pull the alternator back off and take it back to the shop who rebuilt it. Maybe they can figure it out. I just don't get how it tests fine but on the car it doesn't work.

badblackgs

iTrader: (1)

the next step is whats called a voltage drop test. it checks the integrity of the 4 gauge (big cable) when the cable is carrying a load. Its a really good way to check for electrical gremlins. alot of the newer chevrolet trucks and suv's had a really common problem with the radio glitcing out, a/c cutting off, alternator not charging, etc... because the ground cable going from the battery to the engine had a **** ton of resistance. and ohms check would pass but the voltage drop test would fail at over 250 millivolts. take your volt meter and set it to volts dc. put the positive lead on the battery post and the other lead down on the positive battery cable lead on the back of the alternator. i know its hard to get to but you really do need to do a voltage drop test. set your min max button and crank the engine than see what the highest the volt meter read. if its over 200 milliamps it way to high. that means theres too much resistance in the cable and it cant support an electrical load. do it to the positive cable and the negative cable.

kameleon25

Update: I took today off to work on this issue. I had the alternator retested by the guy who rebuilt it and the local oreilly and autozone. All 3 show it as good and putting out 15v with no load and under full load it is doing 14.2v at 100amps. So I replaced the 3-pin plug. Still no go. I even ran the 3 wires from that plug straight to the battery as the only one it needs to charge is the middle one I tried that and all 3. Nothing made it charge. I have tried the voltage drop test and none of them are over 25millivolts. So well within spec. I also tested the voltage at the alternator nipple. It is the same as battery voltage while running (11.4v-12.5v) and when I removed the cable and tested the alternator running it did not show any voltage. So the alternator is not charging at all on the car. I have a new 3-pin plug and all but nothing is working. Any ideas?

bruceb58

So...what are the people who test the alternator hooking up to make it output full voltage? You should at least be able to duplicate what they are doing.

Your alternator has fuses between the ignition switch and the field terminal and the battery and the sense terminal. You should check these. I know you have wired directly to the battery thereby bypassing everything but this is just in case you didn't do that correctly.

You only need to hook up the field wire which is switched to the ignition to make the alternator work. If you leave off the sense wire, it will just go full voltage. The L terminal that goes to the ECU does nothing more than turn on the idiot light on your dash so it can be ignored for now. If you are hooking that up to the battery, disconnect and try again.

I am assuming the alternator has a good ground. You can always test this by hooking up a jumper wire between the battery and the alternator.

Never ever ever ever test an alternator by removing the battery cables while the engine is running. You will blow the regulator in a heartbeat. That includes what you did by removing the output wire off the alternator and running without a load.

kameleon25

I worked more on this again yesterday. I ran an additional ground wire, no change. Additional charge wire from alt output wire to battery, no change. Ran the center pin (field pin) of the 3 pin plug straight to the battery, no change. I am about to pull my hair out. I am thinking I will stop by and get about 20ft of some 4gauge wire with some terminal ends and spend some time putting permanent ground upgrades and an upgraded charge wire on there.

The thing that confuses me the most is the alternator working no problem on the test bench. The only thing I can see different (besides it working) is they ground to a different place. Oreilly grounds to one of the rear bolts on the aluminum rear cover where the rebuilder has an OLD tester that has a pneumatic clamp deal that uses that as the ground through the case but he has contact on the case itself not the mount holes like it is on the car. I know the car is getting ground because the only engine ground is the one on the alternator bottom bracket and the little like 12 gauge one on the firewall but maybe something is going on with the bottom mount bracket that is not letting the alternator get a good enough ground. I will update once I test the ground/charge wire upgrades.

kameleon25

And the saga continues......

Bought some 4 gauge ofc cable today and some ring terminals. Ran straight from the battery to the bottom alternator bolt, not the bracket but the bolt itself. Also ran from battery to the mount point on firewall. Then straight from battery positive to the alternator output. Basically a "big 3" upgrade. In addition I cleaned every single mount point with sandpaper to be positive it made good contact. Still not charging. Ran wire straight from battery to the center "L" or field pin on the 3-pin connector. No charging. I have isolated as much as I can on this car to make it work and no go.

One thing I find interesting is when I have the 3-pin plug plugged in the charge dummy light is on. But if I unplug the plug from the alternator it goes off. Am I wrong in thinking it should be on if it isn't charging regardless? Like if it is plugged in and not charging or if it is unplugged?

kameleon25

Finally got it. I had to think what the difference between the test bench and the car was. It came down to the ground location. So I was thinking about adding some grounds to the rear case cover. When I got the alternator off the car and was looking at adding the grounds to the rear of the case, I decided to pull the rear cover off. This is what I found:



Immediately I noticed a missing screw/bolt around the circled area. So I pulled the alternator off an old engine I have in the shop (same 96 LS400 1uzfe, but alternators are similar enough). Here is what it looked like:



So I took the screw out and put in the rebuilt one. The blue line cover also was not on mine but that doesn't keep it from working so I just left it alone for now. I went ahead and added the 2 grounds to bolts on the back of the case and ran it around to the bottom mount of the alternator when I installed it back on the car. Fired it up and got this:



FINALLY it is charging. Now I don't know if it was that screw that fixed it or the new grounds. I can disconnect the rear case grounds easily enough and see if it still works. If so I will remove them and roll with it. I am sooooooo happy right now!

sugzz

iTrader: (9)

Glad you finally got it to work.

badblackgs

iTrader: (1)

First off, great job getting to the bottom of it and not giving up. but i'd like for you to clarify what it is you did other than put a missing screw in. id imagine that when the rear alternator case is installed, its automatically grounded by being bolted up to the front half of the case. are you saying thats not the case (no pun intended). on our cars, the ground cable attaches to the front of the alternator. please clarify your setup.

kameleon25

OK, so it wasn't the rear half of the case that I took off but rather just the rear cover (the stamped metal part that covers the voltage regulator and such). The screw that was missing looked to be the one that went through the voltage regulator to the case to give it ground. I can pull my 96 ls400 one and take pics to show you since it is basically the same alternator. But when the alternator is on a test bench it isn't grounded by the vase, but by the rear bolts that then give the voltage regulator its ground. That was the missing link. But like I said I will pull the spare alternator apart and take pics.

Mr Jokster

iTrader: (8)

So was it a ground issue, or that screw?

kameleon25

I will test that tonight. I still have to tidy up my cables I ran and put the bottom cover back on tonight so I will test the rear ground removal. I am leaning toward it being that screw though.