xxmariolxx

My 90 ls400 at 190k just started having this issue. it did it 2 days ago. the car comepletely dead no lights no nothing. I thought it was the battery i traded it it was a 2 month old battery. then with the new battery it fired up fine. Yesterday it worked. but today nothing again. what could be causing it. i redid the ecu and put 2 12s in the trunk. but that was a month ago. it just started 2 days ago. please help. i need the car to go to work

fourstars

check your work and make sure the system is not still on when the ignition is off. after that put a voltmeter on your battery and turn all lights off and watch your meter if the voltage drop. if it drops then something is on draining your battery and you need to find it. if nothing happens then check your battery. even new batteries are known to go back. i went through 4 with autozone in 2 weeks, and they all tested good.

you said you redid your ecu? what did you do? BATT, +B, +B1, ISGW, M-REL all has power constant "or" with ignition on. these will turn you ur ECU or other sensors if not wire correctly.

xxmariolxx

did that nothing sucking. i did the ecu a while ago. right now im stubled but i just uplugged the battery ill do more testing on thursday after work. right now ill just unplug the battery nd do that till i fix it. i think it might be the antenna trying to close. it just recently broke again( i bought a new one) im gonna try to disconnect it and see what happens

RA40

iTrader: (6)

Any dash warning lights? How old is the current alternator?

LScowboyLS

put an ammeter in series with the battery and the positive cable, you will then see the drain with car off

then you can selectively pull various fuses and see the difference that makes in the drain, then replace that fuse and pull the next one, this will help you isolate which circuit the drain is in.

I would pick up the original wiring diagram book from either ebay or faxon auto literature.

this will take a little bit of time to solve, but may very well take no money whatsoever

xxmariolxx

no you dont get it i did that. there was absolutely no drain. but for some reason it drains. the alternator isnt the problem. once the cars on it runs perfectly good. im gonna go to autozone since its free to check it. but that cant be the issue.

LScowboyLS

if a new battery is being discharged and run down, it can only be a drain or an alternator not charging. - you are fresh out of other choices.

put your multimeter across the battery terminals with a known good battery in the car, at 1500rpm with headlights on, you should see at least 13.8V DC if the alternator is good.

LScowboyLS

I don't think your test setup was correct, because there is always some tiny amount of drain, such as the clock, the security system, etc. - even on a car that is new off the showroom floor there is some drain, this is normal and correct.

RA40

iTrader: (6)

The chance that the audio install was bad would have appeared almost instantly if there was a wire shorting. The battery will only take so many deep discharges like this. Are you charging the battery between these episodes? In this instance you should have dash warning lights indicating an alt failure. If the dash lights are not working properly, there is another problem that needs to be taken care of as well. There should be stored codes pointing to the problem.

When you insert the key and turn it to the <on> position, do the dash lights come on indicating the system has run through the initial diagnostics?

LScowboyLS

You would think so, however when my alternator failed due to power steering fluid, the dash light never came on at all!

my little $3 cigarette lighter voltmeter from China was indicating 11.2 volts and I was like "uh-oh"

xxmariolxx

ok yes obviously something was there. but very little. it cant be my alternator. one the car tuurns on its good for the whole day itll fire back up. if it sits for a day or 2 its dead

Yamae

All you have to do is the leak test of the alternator. Just set up a current meter in between the terminal +B and the thick alternator cable. Of course you have to remove the negative side of the battery cable while seting up the meter to avoid the shorting problem. After the meter is set, connect the the negative side of the battery cable and read the current. If it's more than 5mA, mostly diodes are leaking.

There's another way too. Instead of touching, terminal +B, You can check the leak current at the 120A alternator fuse too. If the leaking current is big like yours, you don't need to remove the fuse at all. Just measure the drop voltage of both ends of the fuse using a mV meter which can measure down to 0.1mV or below. The reading should be just 0 = none. This is the technique to find out the leaking point.

xxmariolxx

my dads a mechanic. we did this. its not the alternator. iw ent to autozone the alternator and battery were both fine