just put a 2001 ls motor into a si the car has been sitting for a while...the car had a dead battery so we jumpstarted it and it starts...now heres the problem after the jumper cables are taken off the car stumbles out and dies but if you put the cables on it'll idle fine....tried a different battery and alternator but the still the same results....any help is appreciated

 

Bad ground somewhere?

 

Did you put the batteries on a tester to make sure they were good?

 

i dont think that the batt would matter after you jumpstart when the jumper cables are taken off it should still run...checked for loose grounds too no luck

 

If the battery is bad and wont hold a charge the car will die everytime the jumper cables are removed. If you dont believe me then google it.

 

Im ganna save tatrat a post and say blast it with piss!

 

You have a problem that is affecting the battery and the alternator, because neither sound like they are powering the electrical system after the jumper cables are removed.


Ok, here's a good question: EXACTLY where are the jumper cables clamped to when it actually runs?

 

This alternator that you put on was it new or used? Came out of known good car etc? Possible grounding issue. Or other alternator is bad too.

 

alternator fuse is a possibility as well

 

Should still run off of the battery without the alternator.