You know when a vehicle has no passengers it is destroyed after a time.How can i delete that?

When it's within a control region, you should be able to control decay by changing the decay timer via the CP, when you select the CP object. When a vehicle is outside the control zone, decay is automatic, and probably hardcoded. I'm sure you could do something like make giant control regions to stop it, but that has it's own drawbacks, I believe.

Just increase the decay time.

What about setting the field decay time to 0?

Then it might decay as soon as you get out of the vehicle. You have to make the decay time larger like Ace said.

Or, if you want it to never decay, do what train said.

yes i want that they never decay^^THX!!!!