Goddamn electrical gremlins! o.O Help

[Erick]

Ok, we are trying to troubleshoot my electrical problem. Hopefully you guys can share some light in the subject.

Symptom: Battery is getting drained. Alternator reads 13.7v when running. With the battery drained the car runs (not good, but it stays on and is drivable). If I leave it on for a long period of time and turn it off, I can try to turn it back on in the next second and the battery wont have any juice, the starter wont even try to spin.

Even if I had a drain, is it possible to have a drain that wont even allow the battery to charge?

We hooked up the voltmeter to the battery, and the battery reads 11.8v.... we replaced it with a good, healthy charged battery and it read 12.59v when the motor was off. When I started the car, the battery started reading 12.2v... slowly going down.

We checked the reading at the power block on the firewall and that got 13.7v. But the battery only gets the 12.59v... or lower when its on.

So we're at a loss, and the car is driving like crap. Any help? We're thinking maybe the fusable link, but that's only because we dont have anything else to guess... it doesnt even make much sense to us really.

Thanks in advance,
- Erick

[Mike325]

Alternator reads 13.7v when running.

Even if I had a drain, is it possible to have a drain that wont even allow the battery to charge?

I believe that the battery voltage with the car ideling should be around 14.5 volts. 13.7 is low. Now add lights and a radio in the mix and your car will not charge that battery at all or very little. I feel that your alt is shit.

The drain would have to be pretty big to let the batt not get a charge. Have you done a draw test?

About the link. Take a look at it. If it looks ok, then leave it alone. If it looks dirty and that it may be causing a resistance, change it out. Kinda wierd that you will get a higher voltage under the hood than at the battery. Check the battery termanals and maybe look at the wires running from the battery to the block under the hood.

[porsche gt1]

Sounds like you have a short. Have you done the fuse pull test?

[StereoInstaller1]

Erick, try this:

Disconnect the negative terminal. Using 2 large alligator clamps (or whatever you have, c-clamps, whatever) and a digital voltmeter with a range of 20Amps DC, connect the DVM between the ground terminal and the negative terminal on the battery...this makes the DVM act as a bridge between the ground and the battery, capische?

Set the DVM to DC amps.

If you get a reading with EVERYTHING off (doors closed, etc) over .05A, start removing electrical "stuff" until that draw goes away.

Step 1 IMHO, for you, is the alternator. I think your alternator is toast.

Luke

[Mike325]

I believe that the battery voltage with the car ideling should be around 14.5 volts. 13.7 is low. Now add lights and a radio in the mix and your car will not charge that battery at all or very little. I feel that your alt is shit.

I just did the alt test on my 97 accord v6 and this is what I got:

Idle no lights on or accesories: 14.40 volts at the batt.
Idle headlights on, radio on and heat on: 14.30 volts
Car off batt voltage: 12.88.

[NC325iC]

where are you measuring from? well where would i measure from on an e30

[jlevie]

We checked the reading at the power block on the firewall and that got 13.7v. But the battery only gets the 12.59v... or lower when its on.

And there's your problem. The alternator's output isn't reaching the battery and that can be from loose or damaged power or ground circuit. With the engine running, check from the alternator output lug to the engine and then to the body ground and finally to the battery negative terminal a drop in voltage as you move back towards the battery indicates a bad ground.

If you don't find a ground problem measure from the alternator's output lug to the engine bay fuse block and then to the power block on the firewall and finally to the positive terminal of the battery. A good circuit will show zero volts but a high resistance in the circuit will show something above zero.

[ivo316]

If your alternator is toast, you can tell by starting the car and unhooking the battery witht he car running, if it stops, the car is running on power from the battery.

Or unhook your negative terminal from the battery and connect an ammeter to it while running (between the terminal an cable, if it reads negative, your alt is not working.

[Erick]

If your alternator is toast, you can tell by starting the car and unhooking the battery witht he car running, if it stops, the car is running on power from the battery.

Or unhook your negative terminal from the battery and connect an ammeter to it while running (between the terminal an cable, if it reads negative, your alt is not working.

Everyone and their mother have been telling me that you should not disconnect the terminals while the car is running.

And I have also heard that it is possible that the alternator might generate enough power to keep the car running, but not enough to charge the battery.

[mikeedler]

yeah, that stuff doesnt work on "newer" cars, thats an old non computer controlled trick.

Erick, I would say change the alternator, or first, make a new ground wire from it to the block. Its a short at the alt., so a bad alt., or a bad ground on the alt.

just fixed arpads 324td (the evo 8 guy)the other day- replaced the alt. and found out that it was the ground from the alt. looked like there never was one there from the factory, but I made one, and the car runs great now.

[nando]

check grounds first. bad grounds can also cause your car to run poorly..

[ptownTSI]

not all cars do 14.4 at idle. my jeep will only go that high if its really cold out. normally it charges at 14.0