SupSai7

iTrader: (8)

Need some help troubleshooting, I've searched and I have an FSM at my disposal. So I have an S5 vert auto that is bone stock with a voltage drop issue while engine is running and not running. The alternator is brand new and has been tested good. Battery is good too. While the car is parked and running the voltage will drop(within 1-5 minutes) from around 13.5-14 volts, to batt. voltage 11.5-12.5 volts and slowly the car will die because it seems to be running off the battery and not the alt.. Sometimes if I rev it high or "blip" the throttle the voltage will come back up to normal but soon drop and die.
With the eng. off and the key to the "on" position, the voltage will drop very fast(1-3 minutes) until the battery is completely drained. If I pull the main "EGI" fuse under the hood the voltage does not drop. The car can sit for week and the battery will not drain only when the key is in the "on" postion. All voltage checks were done with my M/M at the battery. Also the car has a perfect 700-800 idle and belt tension is good on the alternator.
-Any help is appreciated

satch

iTrader: (1)

Try disconnecting the White/Blue wire bolted to the alternator. If the drain stops then the alternator should be the focus of your problem. This wire is powered by the 30 amp EGI fuse. Chances are either the alternator is wired incorrectly or it is bad even though it was tested as good.

With the negative battery cable disconnected put the meter in amp mode and place one meter lead on the neg battery terminal and the other lead on the neg cable and read the amp drain, then disconnect the wire mentioned above from the alternator and if the amp drain shown on the meter basically disappears then this will also show that the alternator is the cause.

HAILERS2

I'd queston if the regulator in the alternator is any good or not. The EGI fuse on a series five car feeds constant voltage to the alternators regulator and I'm guessing the alt is the one killing the battery power.

You might pull the small plug off the alt and see if the batt goes dead overnight as I think you said. In other words the small plug is the one that is tied directly to the EGI fuse and is what I'm betting is the culprit.

The EGI fuse also feeds other more important items, but only if the key is put to ON or better.

IF the alt is not the problem, the next item I'd suspect is the MAIN relay sticking closed. Pull the four wire plug off that Main Relay and see if the batt goes dead........after you try the alt small plug first.

EDIT: Satch seems to already replied as I was writting this post. Oh well.

SupSai7

iTrader: (8)

Thanks for the reply, I've tried taking the alt. out of the question by disconnecting the plug and the batt. feed wire, so no wires hooked up to the alt. But there is still a drain with the key on, eng. not runnning to drain the batt. within a few minutes. I didn't try the amp test on the alt., I can still try it but if it's completely disconnected I see no reason.

SupSai7

iTrader: (8)

I will test the main fuse today, thanks.

satch

iTrader: (1)

The amperage drain check can be done with or w/o the alternator connected to the White/Blue wire as if there is a drain present it would allow you to measure it and then you could pull various fuses such as the Main fuse to see if it dissipates. You could reconnect the alternator then check for the amperage drain and if present, which is highly likely, then pull the Main fuse and if the drain drops almost completely then you know the alternator is not part of the equation with respect to the drain. The amperage drain test can be used to isolate any drain regardless of its source.

HAILERS2

Main Relay not main fuse.

EGI fuse feeds the alt..........main relay..........and the airbag system if you have it.

See the attached jpg for how to check what Satch suggested IF your meter has a amperage feature.

SupSai7

iTrader: (8)

Yea I meant main relay, oops. I wasn't able to get to the FC yesterday, had to do a brake job on a galant . But I should be able to today, that pic is really helpful. My meter does have the ability to do it. Thanks again.

SupSai7

iTrader: (8)

Here is what I determined so far:
-After doing amp draw tests for an hour on various relays, fuses etc..I came to the conclusion that with the key on eng. off the amp draw had to be normal. Nothing I did made a significant difference.
-I tested the main relay per the fsm and even swapped it out for a known good one from my S5 turbo car. No fix. So I decided it just HAD to be the alternator. Even though I seen this brand new alternator that was on the car, pass all the tests autozone threw at it with there "alternator test machine" with my own eyes last weekend.
-So I swapped the new(tested good) bosch alternator for a old OE mitsu alternator from my turbo car that I'd taken off years ago when I upgraded to an FD alt. But I knew for sure it was good.
Bam! problem fixed, WTF. Full voltage and no drain
I might take this p.o.s. bosch alt. to a different parts store and have them test it. Wonder if it will pass or fail?
Thanks again satch and hailers for the help.