Had some alternator problems.. long story short... Car will start.. idle for a second... then die.... if i leave the key on after it dies the tach bounces up and down.... also my volt meter says 10V but it reads 12.5 V at the battery... Anyone know whats up?

 

well, if I were you, I would start checking grounds, check for shorts, burnt wires, and possibly consider a new (used) ECU (sounds like a possiblity, and a strong one at that).

 

I actualy pulled the ECU... nothing looks fried... the thing is clean as a the day it was made

 

Check your AFM......

 

hmmm... good idea

 

Do you still have ONLY the stock grounds on the car? Or have you joined the "let's throw a ground on everything craze"?

 

I"ve grounded the battery better... thats about it

 

Need some history- what exactly were the alt problems...

Where did you reground the battery to?

 

Battery was grounded to the chassis...

History: put on an S5 alt. i read THREE different posts on how to hook up wires on it.. thought i had it right but they were crossed... draining the battery... Had to get to work so i got i a jump which ended up frying the alternator... so i took it off at work and tested it.. it failed... put on my S4 alternator and tried starting the car and it kinda started... sputtered... backfired... then died... It does this every time i try to start it