Z4M would crank but not start after a successful jump

[sagdast]

I jumped my ‘06 Z4M a few days ago after I let it sit for over 2 months (with only one start in between without letting it run enough). I started it tonight, which would have been the first start since the jump, and on the first try, it cranked for a good 10 seconds but didn’t start. I closed the ignition, waited for a few seconds, and it started just fine. It started normally 2 times after that. Is this a sign of a failing fuel pump or just a glitch from a jump?

[B328iC]

Did you just try to start the car or first put the key in the on position and wait? If you don't wait the fuel pump can't get the system back up to pressure so it wouldn't start right away.

[jclausen]

The fuel system needs to fill and then when it does start it will probably run kind a crappy for a number of minutes also if it's going to sit put a battery tender on the battery, jumping a dead or very low battery is not good, charge the battery and start it again

[sagdast]

Thank you!

[BimmerBreaker]

Likely a small vacuum leak somewhere

[Muzz258]

Or a soft failing inlet camshaft sensor?

[BimmerBreaker]

Dont know why that would be a cam sensor

The fuel system works on vacuum to hold pressure. It there is a vacuum leak the fuel pressure regulator will drop pressure after sitting. Eventually itll drop pressure to "0" and when you go to start it takes longer than usual because it has to build fuel pressure. On consecutive starts it didnt have enough time for fuel pressure to drop all the way so it started quickly since there was residual pressure from having just started the car