[GHT]

Shooting out the tires does not stop a vehicle; except in the movies (where they flip and roll like on the A-Team).
Watch one of those Police chase shows and you will invariably see cars and trucks running only on rims for miles upon miles.
In fact one of the first things the Police do is put down spike strips.

So your scenario is invalid.

Shooting the engine block might work if the bullet wasn't deflected, deformed, blocked or broken up in the process; or you didn't just miss.

In Blackhawk Down one of the Delta Force snipers puts a round right through the engine block of the gun dealer's Jeep; but:
A he is a sniper, not J Q Public, and it is his one and only job in the world to put rounds exactly where and when they are needed.
B he is in a helicopter flying overhead on a parallel speed and course not bouncing around in a chase vehicle.
C he is using a rifle not a hand gun.

A vehicle is a hard thing to stop, better to shoot the man not the machine if your life is at risk.
If it isn't then don't shoot at all.

G

PS Why didn't the guys on "The Unit" on tuesday shoot the engine block or the radiator of the truck when they had the chance, since they just wanted to get away rather than kill everyone?