electrical - car starts then dies, weird tach

[kr8zstang]

i've been troubleshooting some electrical issues. found what was draining my battery, but now the battery has weak charge. when i jump start the car, it runs for a minute, then the tach starts jumping like crazy, then it stalls. (i have an autometer tach). the battery is 3 weeks old, and the alternator checked out good last week. could i have messed something up jumpstarting too much? bad ground maybe?

 

[HISSIN50]

I would charge the battery up, go over the primary electrical connections again, and see how it does.
An almost dead battery can cause some funky issues. And a bad connection definately can (since juice is not making it to the chassis electrical system very effectively, or intermittantly).

Good luck.

 

[Moffa]

maybe there is a bad connection from the alternator to the battery. What voltage are you reading at the battery while the car is running?

 

[kr8zstang]

it's kinda hard to get a good reading. by the time i get outta the car and disconnect the jumper cables, the car starts to stumble. i rev it a few times, then it's dead. but i haven't seen anything more than 11.5v.