Charging system 90% troubleshot. Help

[Benjitis1]

Did a LOT of searching and found tons of helpful info. But i need a little more help. I have a 72 fj40 with an F motor, alternator is mounted on passenger side after gm powersteering added. My battery will die after sitting in the garage for a couple weeks. With a 100% charge on battery, i can drive it around with lights on for 3 hours, turn it off, come back an hour later and the battery is dead. So here is what i have done;

Bought new battery, new voltage regulator, Alternator tested good at the shop, starter has good ground to frame. Checked voltage with key in run position on the following- F terminal at ALT with plug plugged in 5 volts, F terminal on plug while unplugged 12 volts, ignition terminal on voltage regulator is 5 volts.

With key off and everything else off, i dimmed lights in garage and pulled negative battery cable to look for spark, there was no spark, did the same thing with positive cable, no spark.

Checked resistance between F terminal and ground on battery, read 0 OHMS.

Used a jumper wire between B+ on ALT and F Terminal while plugged in to ALT, slight spark, but read 12 volts, there was no slight jump to 14V. Tried jumper again with F terminal unplugged and stayed at 12V. I used the multi meter to perform all of the above tasks. I tried using the led indicatore alternator tester for the last test (B+ jumper to F terminal while unplugged and i got a slight jump up to 13V. only right when i removed the jumper did i get a slight jump in voltage with the small spark. Wondering why the LED alternator tester picked this up but the Multi Meter didnt?

Pinhead, coolerman, anyone have any ideas?

 

[Buckwheat]

First things first

What is the voltage at the battery when the car is running? That will give you an idea of the alternator output. Why you're doing all of those other tests at the alternator is puzzling as they won't provide any useful diagnostic information. It sounds like you have a drain which you can check by disconnecting a battery cable & connecting your test light from the cable end to the terminal. If it lights up, you have a drain somewhere. A test meter is not good for this test but some people use it to read the voltage drawn - a test light gives you an idea of the amps drained. To eliminate the alternator or regulator, the alternator can be full-fielded on the vehicle. The FSM explains it all in detail & I suggest you get one. You're working harder than you have to. Get a 12v test light, too.

 

[Pin_Head]

It sounds like your alternator isn't working. If you apply battery voltage to the F terminal and the voltage doesn't rise, there is no power output from the alternator.

A non functional alternator may not explain why your battery goes dead.

 

[Benjitis1]

Voltage at the battery while engine not running is 12volts. Voltage at battery while engine is running at idle is 12 volts. I have to rev the engine rpm's up quite a bit and then the meter shows the voltage bumping up to 14volts. Should the alternator charge at idle or does it have to be at high rpms to charge the battery?

I have a test light, i will try disconnecting a cable and hooking the test light up to it.

Pin_head -"A non functional alternator may NOT explain why your battery goes dead." Even if my ALT is bad, something else may be draining my battery? Like a short somewhere?

 

[Pin_Head]

You do have to rev it up a bit above idle to see output, but as long as the voltage increases, it is working.

If the battery drains or won't hold a charge, there may be a short (you should have seen a spark) or the battery is bad and won't hold a charge.

 

[Coolerman]

The clue may be the fact that the alternator was moved to do power steering.

Do you know exactly what was done to the wiring?
Was it extended, or was the harness redone, and the wires moved?
Is the regulator still on the drivers side firewall?

Do the obvious things. Make SURE the alternator and regulator cases are grounded. Clean all the power and ground connections around the battery/starter/alternator/regulator.

If your meter will measure DC current, set the meter to read say 2 amps, and put the meter in series with the + battery terminal. With the key off there should be NO current flow (unless you have something wired in wrong). If you read current flow there is something shorted. This would explain the battery going dead even after driving. Though you bought a new battery, it could be defective or already destroyed due to being discharged too deeply too often. Use a known good battery for testing.

The fact you have to rev it up beyond whats sounds normal to get a charge is also a clue. The old regulator can actually be adjusted for it's pull in voltage. The FSM has the procedure. Check to see if it's within specs and adjust it.

It may be necessary to re-do the wiring if it was hacked....

 

[Benjitis1]

I did the power steering myself. I lengthened the wires and bought a new plug for the alternator. New regulator is in factory position on drivers side of firewall and has a good ground. The alternator is also well grounded. I cleaned all connections. I hooked up meter in line with + battery terminal and cable, its not drawing power with everything turned off, so thats good. Also used test light between terminals and battery posts like Buckwheat mentioned, light did not light up. I fully charged my battery last night. I'll take it in to have it tested today to make sure its still good. Then I guess i play the waiting game and see if the problem re-occurs. I'll try and see if i cant get the procedure to adjust the regulator...now i just need to find a FSM...

 

[Coolerman]

You can access the FSM and schematics here :Coolerman's Electrical Schematics and FSM File Retrieval

 

[Benjitis1]

thank you.

 

[Benjitis1]

One more thing. When engine is at idle, all switches, heaters, are off, the ammeter reads -2. When i turn low beams on while at idle, ammeter reads -15. When lights, and heaters are on, ammeter reads -22.5. When im driving down the road at 35mph and the heaters and lights are on, the ammeter reads between -2 and 0. Is that right? How the heck does the battery charge if its always in the negative?

 

[Pin_Head]

It shouldn't read negative if the alternator is working, unless it is wired incorrectly. Is the wiring stock? If the alternator is wired directly to the battery, rather than going through the amp meter it will always read negative, even when it is working properly. If it is wired correctly and it always reads negative (even if you hot wire the F terminal) then the alternator is bad.

 

[Benjitis1]

Im sure its wired right. I took the tape off and seperated each wire and marked which was which.When i rev up the motor it will go into the positve side of the ammeter to about +5 at most, which would prove that the alternator IS working, correct? Are there any other ways to check the alternator i may have missed?

 

[apeterson]

your alt is not working.... check out my build thread.... last page... I just put in a GM alt. in a 74 with the same deal... I do not use the factory voltage regulator.

 

[Benjitis1]

Nice looking rig apeterson. How much did that alternator run you? I think im gonna have my alternator tested again, but by a different shop, just to make sure. I dont wanna replace something that isnt broke.

 

[apeterson]

$82.03 all set up the way I wanted, if your is working just pay them to put a diode in it, internal or external and run it like mine... super easy!

 

[Pin_Head]

It sounds like your alternator is working, but it is weak and cannot keep up with loads, like the lights. After you discharge the battery a bit by cranking the engine for 15-20 seconds with the coil wire pulled prior to starting it, the alternator should put out a lot of power to charge the battery.