Okay, my friend stalled my 7 once while driving and while trying to start it back up, the battery ran out of juice real quick and so it needed a jump. Got it home, decided to check the alternator...

Took it to Kragen to test it, alternator tested fine (out-of-car test). Took it back home and re-installed it, tested it at Kragen again, in-car this time, tested to be bad (no charging voltage, no diode ripple detected). Took it out right there in the parking lot, tested out-of-car, tested fine.

Wondered about problem in wiring, the thick wire carrying the voltage from the alternator to the battery seems ok. So I then tested the wire on the top of the 2-wire connecter (the one that controls the internal regulator) as per the FSM CD, tested to be putting out like 11.7 volts with the key on, while the battery was at like 12.5 or something. The service manual says that if this wires voltage is lower than the battery voltage then there is a problem in the wiring harness.

...So I have 2 questions really: How would I go about hunting down this "problem in the wiring harness"? (I have no clue really where this wire leads, and its way confusing to try and look for it).

And question two: While testing the alternator at home in the car, the alternator was putting out like only 0.5 - 0.7 volts while running, so I was wondering, would that small difference between the battery voltage and the voltage received in the wire I tested (going to the internal regulator) really make THAT much of a difference?

....Any help would be greatly appreciated, and sorry for the long post, I just wanted to make sure I got all the info in there.


PS- I am almost 100% totally positive the alternator itself works fine, since it was tested on two DIFFERENT machines outside the car (two different Kragen locations) and tested fine (we even tested the new aftermarket alternator and compared the results to mine, and they were identical). I also even asked point blank "Is my voltage regulator working then?" and they said yes, the machine tested that too and its fine.

...Thanks alot in advance, if I get this sorted out Im almost sure it will solve half my idle problems (a/c killing my engine at idle).


...Oh yeah:

'87 TII Stock

 

Whats your zodiac sign?

Sounds like a dead alternator if you are only getting wierd voltage. hook up volt meter to the battery. you shoulc see about 13 or so at idle (or more) and about 14-14.5 at say like 2500 rpms.

If you need, I have a spare alternator here that flickers the lights at idle, but it charges at 14.5 volts.

 

...Yeah, it sounds alot like the alternator is dead... but how would that be possible if it tested fine twice? Why would it output the voltage on a test machine but not in my car?

 

I have no idea. Maybe check the grounds on your car??? set your meter on ohms and check from the top of the alternator to the neg bat terminal. The lower the number the better. I think mine is pretty low now that I reground some crap.

Maybe the machine spins it faster than your car?? i dono

 

no, I checked the ground already, its good. ...so far this car has been a real ***** to figure out. Nothing has been an easy fix yet. (normally, it would be a bad alternator, but no sir-ee, not in my car. That would be too logical and easy, we will not be having any of that here)


...anyone have anything else in mind?? Im really running out of ideas, and fear I may have to take it to the dealer

 

If the alternator checks out fine.

There might be a short some where drawing power from the battery, and the whole system.

Trouble shooting this could be a real pain. Look for loose wires elsewhere

 

so when the car is running, there's not really any voltage at the battery? And the alternator tested fine in the shops......

Either the alternator is intermittently bad (intermittency is the DEVIL!) or there's a short in the line betwen it and the battery...Run a new wire from the alternator directly to the battery's positive terminal. See if that helps.

Cory

 

If it was intermittently bad, would that make it work always outside the car but never inside the car? Because it is not a random malfunction, it just simply doesn't work inside the car, and then when yanked out and put on a tester it works perfectly. Very wierd.

 

....Just wanted to give this post some closure (even though it is really old), just in case someone has a similar problem and does a search. A long time back when I finally had figured out the problem (actually I had taken it to a shop for other stuff and asked them to check out the alternator while they were at it)

...I found out that the reason the alternator was testing fine was because it would fall flat on its face when any load was applied to it- not a load from a short or anything, but just the load being drawn from the car stock. And so that was the reason it would always test as dead in the car, and fine at the auto-parts store (since their testers do not apply any load). So thats how it happened- kinda sucked, and caused major frustrations, but its cool now- I replaced it way back then when I found that out and have not had any problems with it since (I've had plenty of other problems since then though, hehe)

So, yeah, theres the conclusion for anyone who may need the info in the future. You may now let this post drift off into oblivion.