Car battery drained overnight

[mentordrift]

Not sure what's going on, just started happening a few weeks ago:

History of the car - 1995 240sx with RB25DET motor swap. SAFC 2 wired in, dual electric fans running off thermo-controller off battery for power. Everything else is wired in elsewhere.

The car is currently in storage, but I went to pull it out last week, dead battery.
Charged it up, starts fine. Shut it off, left it a few hours, started up fine again. Battery showing 13-14 volts through SAFC

Came back this week to drive it again, same thing. Charged it, started up, shut it off, left it a few hours, charged again.

Before I start swapping out alternators, starters, and batteries - has anyone else experienced this?

My first thought was it is the battery, but it's new(ish) from 2006. It may be time to get a new one.
The starter is relatively new, from 2008.
Alternator is from 2009 - after trying a Quest retrofit, I went back to RB25 OEM.

Since the car is taking a charge when using a battery charger (not jumping the car), am I safe to assume there is a short coming from a positive wire somewhere in the car? I can't figure where it may be coming from, though, as the harness under the dash is unfooledaroundwith, and the only thing spliced into the main harness is the SAFC.

Alternator tested fine at Autozone.

Where else can I search for gremlins?

[mentordrift]

Multimeter black to negative, red to cable shows .07, pulling the alternator fuse drops it to barely .02....looks like I found it??

[slider2828]

Weird your alternator is pulling.... It shouldn't be pulling when its off.... Check other fuses....

[rcdad123]

yeah, start pulling fuses out till the amp draw goes away or lowers significantly. once you find the fuse that lowers the amp draw, start looking for short or anything that might stay on on the circuit that the fuse protects.

[Mangudai]

Multimeter black to negative, red to cable shows .07, pulling the alternator fuse drops it to barely .02....looks like I found it??

Sounds like you found the problem.

[slider2828]

But doesn't make sense the alternator is drawing current..... its gotta be something else.

[rwtf]

if you have a sub or anything check that.

[mentordrift]

This may be a hella newb question - but would have a higher amp fuse draw like a short? I had never checked the underhood fuses, and found a 120 amp fuse on the main fuse.

I just spent $20 at Nissan for a new main fuse, and am waiting for the battery to charge up so I can check it. But my assumption is that the draw will probably be between the alternator and battery?

[s34n]

Sounds like a parasitic battery drain.

[Mangudai]

But doesn't make sense the alternator is drawing current..... its gotta be something else.

It happens. Could be a bad diode or voltage regulator.

[mentordrift]

So, I got the car started this morning, new fuse in, battery voltage at ~11.8-12.9 ignition off, car ran for about an hour, then I shut it off.

Went to restart the car, and it was just a dead click again.

fffffffuuuuuuuuuuu!!!!!!!!!!

[mikeroy420]

Sound like the altenator is bad. I dont really know what they test when they do an altenator test, but I have a had altenators that test ok not work.

[mentordrift]

here's the hardest part of this diagnosis - when the car is running and the negative cable is removed, the car stays running.

From what I remember, if the alternator is bad, taking off the negative cable with a bad alternator will essentially stop the car from running because the battery is no longer charging.

It seems to be a grounding issue, as replacing two of the engine grounds made it retain a little bit of a charge - enough to get the car juice to start without jumping or charging....

[slider2828]

Your batt could have died cause cca where too low..... takes a lot of juice to crank a car... Did you run it around the block a couple of times? Batt doesn't charge till at least over 3k rpm

[Walperstyle]

From what I remember, if the alternator is bad, taking off the negative cable with a bad alternator will essentially stop the car from running because the battery is no longer charging.



Under your situation, if its a near dead battery, yes it would die right away. If you had a new battery and you disconnected the alternator. I believe you could potentially get another 3 hours out of it before it would die.

...I could be wrong, last electrical issue I had was on my 65 chrysler, and it had an external regulator.

edit: I believe you are right though.

[ericb382]

First step just because it's so quick and easy. Check the battery voltage with the engine running, should be ~13.5v. If it's below 13 after the motor has been running for at least a few minutes the issue is alternator related.

Realalistically, it sounds like your alternator is draining the battery. Do another amp draw then disconnect the alternator and see if it drops, this will tell you if the problem is the alternator or the wiring going to it. Are you sure you have the alt hooked up correctly?

I'm going to go ahead and assume that when you said your key off draw is .7 you are talking about .7A, but next time you may want to include a unit of measure as .7A is way different than .7mA, etc...

[mentordrift]

Your batt could have died cause cca where too low..... takes a lot of juice to crank a car... Did you run it around the block a couple of times? Batt doesn't charge till at least over 3k rpm


Yes, just over 1.2 miles driven, but nothing over 3k for a long period of time, which leads to my next area of interest....


First step just because it's so quick and easy. Check the battery voltage with the engine running, should be ~13.5v. If it's below 13 after the motor has been running for at least a few minutes the issue is alternator related.

Realalistically, it sounds like your alternator is draining the battery. Do another amp draw then disconnect the alternator and see if it drops, this will tell you if the problem is the alternator or the wiring going to it. Are you sure you have the alt hooked up correctly?

I'm going to go ahead and assume that when you said your key off draw is .7 you are talking about .7A, but next time you may want to include a unit of measure as .7A is way different than .7mA, etc...


The car after being driven around the block reads just about 13.6 on the radar detector AND safc, so both are reading the same voltage.
AFTER letting it sit, it dips down to the 11.5 range, a full 2 volts lower...I'm pretty confident that the alternator is hooked up correctly, although there is a "splice" from the ground that I do not like.

I am in process of removing the alternator to have it bench tested at VatoZone just for piece of mind. Best case scenario, it is okay, and I need to trace wiring. Worst case scenario, I have an extra Quest alternator laying around, and will just reinstall that mama-jama for the time being...

When the key is off, I am drawing .7A, yes. When the main fuse for the car was removed (previously a 120A bladed fuse), it would drop to a normal level (.2A), now with the correct fuse (75A) in, it is .2A with the fuse in....I loathe electrical problems.

[mentordrift]

So since I couldn't find any short or weird happenings with the wiriing, I decided to check the rest of it all....and put on a new intake manifold while I was at it. lol


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