DON'T TOUCH THE CAR Achievement
DON'T TOUCH THE CAR40
Finish a chase level with at least 75% of the Ecto-shield up.
Check the Achievement Trading Thread and find 3 people to do this with. You have to defend the truck while driving through the city, blast as many of the flying skulls and gargoyles as soon as possible. Basically never stop shooting. It shouldn't be that hard if you find 3 good players and play on the 4th level. It's almost impossible to do with the AIs since they aren't shooting at all, if you aren't really good that is.