My swap is drawing to a close now I'm driving the cruiser and working out the bugs. one of these bugs has me completely stumped. My battery keeps going dead and it appears to be the alternator. I've replaced it with a new one and it no works either. Anybody had a problem like this or have any ideas would be great.

VORTEC... I'M DROOLING!!!!!

Do you have the correct alternator? You probably do so what I'm thinking is you have something electrical not hooked up right which is sucking up all the juice from the battery. Test another battery also, maybe this one just doesn't hold a charge.

Yeah the vortec is nice I just wish I could keep the battery charged. The alternator should be right. Is there any reason the engine shouldn't keep running once disconnected from the battery as long as I keep the hot wire from the alternator in contact with the wire to the computer. This is the way I traditionally test alternators, of course this is the first time I've messed with anything computer controlled.

Have you installed a charge indicator light on your dash? You didn't mention what year of engine you have, but in at least the GEN II engines you need to have a light bulb or some similar resistance in the circuit or it will not charge. You can see how this works in the charge curcuit electrical diagrams. I don't have my shop manuals with me, but they do include a precedure to test if the alternator is working properly. Have you tried that?

I agree with Jack, on the newer Alternators you need the charge warning light or equivalent resistance. Also, are you running a battery isolator? Unless you have gotten a newer isolator designed to allow the alternator to sense the voltage at the battery they will not let the alternator charge-b/c it will not "see" any voltage from the battery(giant diodes in isolator prevent this)
Check www.alternatorparts.com for info.
-Brett

Also, the engine should stall once you remove the battery lead and attach the computer to the alternator terminal. This stems from the fact that the alternator will not sense the battery voltage and will stop charging. This is a safety desinged into the newer GM alternators to prevent overheating from overcharging-due to a very low battery voltage. So, when the wire to the battery is disconnected, the alternator will not see the voltage at the battery, therefore thinking it is "dead" and it stops charging to prevent overheating. Not all alternators work this way but the CS130 and newer GM alternators this is common...

Check you wiring on your alternator, and most likely you will need the charge warning light. Install it and see what happens.

-Brett

Originally posted by BarnWrencher
Is there any reason the engine shouldn't keep running once disconnected from the battery as long as I keep the hot wire from the alternator in contact with the wire to the computer. This is the way I traditionally test alternators, of course this is the first time I've messed with anything computer controlled.


Having worked in an auto electric shop before, you should NEVER unhook the battery lead while the engine is running! You can get voltage spikes that can blow out anything electronic (You spent too much time getting all this stuff running to blow out your ECM). Air bags can go off, ECM can toast, radios can fail. The disconnect the battery trick was only used on older generator charging system vehicles.

What alternator do you have (year & model it is from), do you have any isolators or anything, does it show any charging voltage while running (at alternator stud and battery), have you tested for parasitic draw from the battery (drain battery while sitting)?
Also, what year model is the vortec/harness/ECM from?

It's a 96 motor, wiring harness and ecm. I do not have an isolator or an indicator light. The alternator only has one wire coming from it which I have been told is for exciting it. Would I hook up the light in series with this wire? And I suppose the isolator would connect between the post on alternator and the battery terminal, or starter post. Does this sound right? Any more ideas?

Barnwrencher,

Where did you get the alternator?

DITTO on “NEVER DISCONNECT A BATTERY WHILE THE ENGINE IS RUNNING”. Most of the modern vehicles electronics are designed to survive, but not a good idea. Lots of the designs from the 1980’s were not designed with the disconnected alternator in mind, and could blow out lots of electronic items. Most of the systems starting in the 1990’s were designed to allow for the accidental disconnect of the battery, or a tow truck using a 24V jumper (spins that starter really fast!!!) system.

The later (OEM) alternators have the two large wire connections (+ & -) and an additional two spade terminal connector for the “lamp wire” and “battery sense” circuit. Sounds like you have the aftermarket self exciting style (very common on street rods, and from places like Summit Racing… ).

The ONE wire alternator is the self-exciting type. Once you get it revved above 3000 rpm, or so, it will turn itself on. All you need is TWO wires. The "+" goes the battery, and run a second wire - of the same size, from the alternator to the battery ground for the return path. Spotted one alternator with rubber bushings in it for vibration resistance... well, it needed a ground wire attached to it, for the alternator to function correctly.

Next item: Simple test light. Engine off, key off. Disconnect the "-" side of the battery. Hook up the test light in series between the battery and cable. The light should remain off. For fun, turn on the headlights... test light will glow brightly, but the headlights do not come on (not enough current flowing through the bulbs for them to light up... your test light is acting as a current limit).

I’ve been tracing an odd short on my ’79 FJ40 for months. I’ll park, and let the vehicle sit for a couple of weeks… starts right up. Next time the battery is dead in a few days. Grrrrrr. Very time consuming to trouble shoot as it occurs randomly.

Tom :usa:

Ok, if you have kept the original harness, including the power cable from the battery to the generator, the isolator is in that cable. The role of the charge indicator lamp is shown on page 8A-30-1 of the 1996 shop manual. If you don't have the manuals (and you should), a copy of that page is HERE (http://darkwing.uoregon.edu/~jrice/cruiser/VorteCharge.gif)

Examination of this diagram shows why you need the charge indicator lamp or similar resistance. The lamp is connected between a wire coming off the RUN pin on the ignition switch (supplying power) and pin C3 on the C100 connector. At the other end, the lamp wire is part of a two-pin connector on the back of hte generator (I use GM's terminology);)