Hey guys, so I have an 02 wrx with 97k miles. Not much done to it but intake, exhaust and cobb AP stage 2. I went to pump gas today and after I got back in my car to start it, battery went completely dead. Got someone to jump start it, but once I removed the jumper cable, my car died. So I left it there and came back with a different battery and started right up. Drove home, took alternator to go test and passed. Bought a brand new battery and put everything back in and it started up. Decided to test the alternator so I disconnected the battery while car was on and it instantly died. Drove it to the shop to see if they can see anything wrong with it and all voltages were normal. They disconnected the battery while car was on and it died again. Shop said they dont know, alternator is charging normally, battery is good and they cant seem to find anything wrong. Anyone know what could be happening? Drove it home and does the same thing once I disconnect the battery. Maybe I need better ground? Thanks in advance!!
Stop disconnecting your battery with your car running. And don't take it to a mechanic who does. That was a valid test in the 50s but not on a modern car. When you disconnect the battery the voltage can spike and ruin things. The battery acts as a capacitor when the car is running to regulate voltage. Without it your voltage will spike. It can spike enough to cook an ecu. It can ruin the diodes in the alternator. Hopefully you haven't ruined anything yet. There may even be curcuitry that needs it to function and the car wouldn't run without it normally. If you have 13.5-14.5 ish volts running your alternator is good. If your battery passes a load test it is good. There is a load test for alternators too. The car needs a battery to run. Please do yourself a favor and don't disconnect it with the car running.
Alternator is running at 14.5 volts. Battery is brand new. So what can it be? And yes I only disconnected the battery twice. But I still don't know what's wrong. I took it out to test drive it again with the new battery and once I shut it off and try to start it, same thing, battery went completely dead.
I didn't have the volt reader on me. I just had my girls car jump it for 15 min and it stayed on long enough to get back home.
Interesting the battery will go dead with the alternator working. And that quickly. I would check connections at the battery, ground starter, and alternator. Use a volt meter to check the voltage at the alternator + and the battery+ they should be within .1. Use the engine and battery grounds shouldn't be any difference. An inductive clip on ammeter would tell you how much current is coming or going to your battery. It will have a big negative draw when you startup then it should read positive 20 or so amps right after startup then go down to just a few amps positive. If it's negative while running your pulling power from the battery. If you have a not stock sub try disconnecting the amp from the battery. Check all the fuses. A bad starter solenoid sometimes will act like a dead battery when it gets hot, but that doesn't explain why it died with the jumper cables removed. Otherwise my money is on a bad connection or a short to ground somewhere. Good luck. I know electrical problems can be frustrating. Post what you find.
Replace the ground from the frame, to the negative terminal (it is the terminal), to the starter bolt. And clean up the spots. I've seen this cause this a couple times. Or else you could have a junk new alternator, seen that also.
Do you have the Hellas on your car? Search for corrosion spots or loose connections. There's a short somewhere.
If there was a short there wouldn't be voltage across the battery when hooked up, nor would it run. ...not to mention the likelihood that the battery would have melted down by now (and the car with it).
Then that wouldn't explain why it dies when the battery is disconnected...unless it was 'switched on' in that condition...which gets back to the point; a shorted battery will lead to very bad things.
Still havent figured it out. So far everythings running fine again and it hasnt died. Hopefully everythings ok now with a new battery. Ill also be checking for a parasitic draw later. Hopefully I find something.
