I have a 75 280z. I left my lights on, and about 6 or so hours later i couldnt start my car. I got a jump start. Car ran normal for about 5 mintues, then died. Wont crank over. Got another jump start. Ran fine until i was parking. Died again, when i let off the gas. The battery was repalced a few months ago. Is the alternator bad, or the battery is bad? I tried to push start it, i dosnt want to turn over. thanks in advance jesse.

when the car would run did all the electrical things run normal? Lights normal brightness and guages running correctly? Was the amp guage reading in the positive side? Sounds like either an alternator or voltage regulator . Good luck

I had a similar problem and it ended up being my voltage regulator. My battery blew up and ate a hole through the wheel well so beware of driving the car any great distance not knowing exactly what's wrong.

A buddy of mine said you can check the alternator by taking a screwdriver and putting the tip of it on the middle of the backside of the alternator. He said there should be a magnetic pull when you do that, otherwise, your alternator probably isn't charging the battery. (I know, another "my buddy" but it's worked for me in the past.)

Make sure your alternator belt is tight. Put your battery on a charger for a couple of hours and go from there. If it still won't turn over, battery.

thanks guys. When the car ran everything seem to be working. I am getting the car towed home after work. Then i am going to tighten the alternator belt and charge the battery. Hopefully that will do it.

jesse

Being a 75, it has a voltmeter. What reading do you get when it's running? Should be above 12 approaching 14 when it's running which would indicate that the charging system is working properly. Should stay around 12 volts when the car is turned off. If not, the battey is either not fully charged or bad. Check these things after charging the battery.

I think Ed ,nailed it. Charge the battery. Sounds like you havent driven the car long enough for the alternator to recharge the dead batt.