Okay, I know it's not a ford, or a truck, but I need some help with my girlfriend's car. It's a 91 dodge spirit, and it just started playing the game where the battery is always draining when the car is shut off. I tested the battery, which is fine, and I can pull a wire off the battery and it keeps running (suggesting the alternator is okay). There's no lights being left on, and I went through the fuses with a multimeter and it looks like the only things with power should have power. I couldnt find any shorts anywhere i've looked either.

Any ideas? The partsamerica website lists an alternator voltage regulator for these...that's probably attached to the alternator on these rigs, eh? If one of those goes bad, what are symptoms? I'm kinda stuck, and this is the car that we drive to school to keep the gas in the truck

THANKS!!!

 

When the voltage regulator in my 77 F150 went bad my battery would die once in a while while parked, but it would also overcharge the battery and cause it to leak.

Is there an underhood light that is staying on while the hood is shut? My mom had a Pontiac Fireturd that did that.

 

if it dies after sitting for a while, what you need to do, is go through the fuses with the key off, and see what is drawing power when the key is off, and then go from there. If you drive the car, and it runs, but when you shut if off the batt is dead, then i would think regulator.

 

This is what I was trying to do. Everything's dead except one column. It has power to it, and all the fuses that are powered by that column use a little power with the key off, but it's only maybe 8 volts, doesnt seem like a short, and it wouldnt be something left on.

The alternator is definately charging, since when the battery is disconnected it will keep running. The thing is the regulator in MY truck was fried when I got it, and it really just shorted out inside, letting the power flow from the battery to ground really slowly.

 

well, if its a cheap part, then replace it. I would think with the key off, there shouldnt be power to anything

 

There's gonna be power to some stuff (headlights, cig lighter, dome lights, etc) I just dont know why there would be any draw.

 

What i meant is with the key off, and everything else off, there should be no draw, the headlights and lighter should draw unless you turn them on....

 

see how many amps is going through that fuse, with the key off and all acc/ turned off (make sure you close to door) there should be 0 amprege to everything, except the stereo or the clock, only thing that should pull amps at power down is things with memories. and even then you probly wont be able to read it unless you have a digi ammeter

 

brent is correct

 

With the engine off, connect an ammeter across a battery post and the connector on the battery cable and make note of the total current draw. Make sure all accessory lighting is off; remove bulbs if needed. The current draw should be tiny (miniscule); I would expect it to be under 100mA (milliamps). Make a note of this number. Now go through the the fuse panel and remove each fuse one at a time and hook your ammeter across the fuse contacts. Current draw on anything other than the radio and computer is reason for concern. The total of your current draws should equal what you found when you hooked up the ammeter at the battery. If they are not, then you need to see if there is another circuit(s) not serviced by the fuse panel, something like maybe a fuseable link. Once you find it, hook the ammeter across it and look at the current draw. Also, with the ammeter hooked across the battery post and battery cable connector, I would like to think that you could pull the wiring on the alternator and see if your current loss drops significantly. This just might be a great place to start. Finally, when you're going through the fuse panel and you find an unusally high draw, that will be the circuit that you need to troubleshoot.

I really don't know how to diagnose the regulator itself but I bet what I noted above will do the trick. If you need to borrow a digital multimeter gimme a hollar.

 

One of the most common misconceptions that I see in the auto repair industry is the mistaken assumption that because an engine countinues to run with the battery disconnected then the alternator must be good. Not true at all. If anything it means that the alternator is producing enough voltage/current to operate the ignition system. That has nothing to do with how well it does it job of maintaining a good 12.6 volt charge on the battery. The alternator must be capable of maintaining this charge AND take on the work of handling the loads of the whole electrical system.

This is done with the voltage regulator. Most regulators today are diodes placed inside the alternator. The internal regulator can create a draw on the battery or even worse can completely short out and smoke out some wires. I have seen both.

 

Good point Greg. The battery actually runs everything; the alternator simply maintains the battery charge. Alternator output is far less than the amperage a fully charged battery can deliver.

 

Yeah, I pulled the alternator a little earlier tonight, gonna stop by schuck's on the way home from school tomarrow and put it on the tester. I woulda dove further into wiring, but I dont have an ammeter, just a really basic multimeter. It was fun finding the most redneck way to relieve the belt tensioner Imagine a wrench, speaker wire, a wood clamp, and some zip ties

 

The thing is, you did the alternator trick wrong. After starting, take off the battery terminal THEN TURN ON THE LIGHTS. If the car runs, alternator MAY BE ok but it may not also, only charging enough to maintain run.

Also, you may be getting only a surface charge on your battery. It can show charged but in actuality is really not charged. Check it with hygrometer (sp?) to verify specific gravity.

Over the years, I've had several vehicles that had batteries that built only surface charge.

Other option is that you have something which is continuing to draw power with key off. There is an easy test for this, but it escapes me at the moment. Had something to do with taking out the fuse for anything that remains on when ignition is turned off (i.e. radio/clock, etc) and check voltage. Open a car door and you should see a significant voltage drop, if not, something else is on. (Well, that was the principle, I forget the exact test procedure)

 

DO NOT PULL THE BATTERY CABLE WITH THE ENGINE RUNNING!

I have personally ruined an ignition module by doing this. If there is a problem with the alternator, the only thing holding the system voltage down is the battery. Radios ignition modules and computers can be ruined by the spike and or the uncontrolled voltage that results from taking the battery cable off with the engine running.