GrandAm 1993 V6 Battery drain.

[wagnerl]

Replaced battery twice in 3 months, WalMart units, the second was $56. My regular drive is afternoon to the office, 15 miles away, AC on. Park there for 10 hours, return home around midnight, another 15 miles, this time with lights and AC on.

After 10 days of new battery, sudenly at the next afternoon car presented very deep discharged battery, internal lamps show very dim, no start whatsoever, even the open door buzzer sound very weak.

Checked everything, cables, contacts, everything is clean.
Took alternator out, send for maintenance. It was disassembled, regulator and diodes replaced, reassembled, generating 14V @ 160+A in high speed test at the bench. Installed at the car.

Two days later battery was completely flat.
Used an external AC charger, let battery charging for 24 hours. It started with 2A, 30 seconds later was charging with 7A, after 15 hours or so the charging current wend down to 3A and staid.

After this 24 hours charge, no problem whatsoever for another 7 days, until the weekend. Car stayed parked Saturday and Sunday, monday afternoon battery was flat, completely. Requiring another external charge.

The problem is NOT the battery, NOT the alternator. I even removed the fuse that feeds the internal lamps and radio. Problem already happened with that fuse removed.

It seems to be some kind of short circuit that only happens after the engine cools down. Why? because for more than once I removed the battery negative cable, installed a series 10W lamp and measured the voltage drop over the lamp. I am able to measure the weak 5mA consumed by the (memory) turned off radio (with that fuse on), around 60mV drop over the lamp. I monitored that lamp voltage drop for hours, trying to see a higher current at any moment, but nothing. It seems that something, after some time, starts to drain many amps from the battery in a way to flat it down seriously.

I also thought about the alternator being not energized at some time, but the inner coil feed is directly from the ignition key, isn't it?, what would not recharge the battery during that time, but it will not flatten the battery suddenly, wound't it ?

If the alternator field is off for some time, it wouldn't turn on the red battery indicator at the dashboard? It never happened while driving.

As a matter of fact this car was bought new in 1993, and I remember the dealer needed to recharge its battery to start it at the parking lot, it was the only red V6 two doors, so...

Any hint?

[catback23]

the alternator field is controlled by the voltage regulator. So the regulator controls whethers it's on/off/weak/strong. You did alot of good checks but instead of using a lamp I would have just put a voltmeter between the negative cable and the negative terminal and read the voltage. It should be pretty low if only the ECM and radio are drawing power for memory. If it's anywhere near 12 volts then you have a drain. Try disconnecting the radio memory and the ecm fuses/connections. The draw should be absolute 0 in that state, if it's not then you have a stray draw somewhere. Also do you drive during the weekends? If you let your car sit for the weekend the draw may just take the weekend for it drain the battery to a no start state.

[wagnerl]

Yes, the no-drive during weekends increase the problem. The drain during the night (8 hours) is not so bad since at the next day still some juice to drive the start motor, but a 48+ hours drain really dry it down.

I would love to have the electric circuit drawings for this car, since the book I bought at the parts store gives me only block drawings, it doesn't show all the fuses not the overall picture of the connections.

Using a voltmeter I found out that half of the fuses at the fuse-box are hot (12Vdc) with ignition key off. It means that more than I thought is able to consume battery current while parking, in case of any temporarily short circuit, or a bad leaking component.

For my surprise the ECM fuse is not hot, is powered by the ignition key switch, but part of the ECM (memory) should be hot.

With the ignition key off, I removed one by one of those hot fuses and measured the voltage at their empty socket, in each one no more than 0.01V were presented, that is more electric noise than current flow. All of the hot fuses presented no current. I need to do it at night, or during a weekend to make sure it still like that during battery discharge.

With a multitester I measured the negative pole/cable current (with interior lights fuse removed), it was only 3mA (0.003A), what I think is the ECM memory consume. It leads me to think that the current leak is intermitent and happens during the night for some reason, when the engine cools down. Cooling down, some wire retracts, touch some part of the engine/chassis, in time the insulation was wasted, a medium current short circuit, battery dries out in time.

Today battery presented 11.78V, engine started ok, battery voltage jump to 14.3V during engine run for a minute, returned to 12.3V after engine off.

I know some things are unfused and hot, as starter motor and solenoid, a current leaking in those parts will be difficult to discover.

[catback23]

The ECM as you found out doesn't have a fuse in the fuse block for memory, you would have to find it's separate circuit or disconnect it entirely to isolate it. Intermittent shorts related to temperature are often found in the engine compartment so you may have narrowed it down to one part of the car. As for circuit diagram you could try your library or buy one from the dealership.