It's feasible. But it's a larger device than shown in the movies. I doubt it could be effectivley shot at the car.
There are two variants, the above described blanket and a bowl sized turtle like looking thing.
Both are supposed to zap the shit out of the car.
By the way...it's NOT EMP. It's just a really strong current, as in lighting like. EMP is a REALLY strong radio wave.
Also, cars are immune to EMP due to the rubber tires, the whole car acts very much like a Faradays cage. For EMP to effect equipment, it needs to be grounded. Cars are not linked to the ground so EMP will have negligible effects. (Although it could have odd effects on more sensitive circuits like GPS)
The reason the blanket/turtle like technology works is that it acts far more like lightning and generaly directly hits the engine block frying the fuel injector.
In the end the technology is very much incomplete and unreliable. To deliver a charge powerfull enough to blast an engine by pure luck a powerful flash capacitor must be used, those tend to be rather expensive (also used in rail guns..yes they exist. Navy has some. Yes they're HUGE).
So in other words you'd be trying to shoot a big fat capacitor ( something like http://www.powerlabs.org/images/caps.jpg
) and some way to grip it onto the car. The gun itself must contain the proportionaly large battery (think a trunk full of car batteries) and must charge the capacitor before firing it. In the end I'd say that if your car got hit by a gun that fired those things, I'd be far more worried about the structural integrity rather than the electric system.
Oh and I JUST realized that even if you got the above figured out, you're still in bad shape cause you need some way to force curent throug the engine/injector. As is it'd just go from one contact to the other...it may melt the metal where it's touching the car but thats about it.
Also it's very likley that even if you car does get hit, the engine will not be effected but instead the current will flow through the frame of the car bypassing the engine.
Anyway....2fast 2 furious was a disgustingly bad movie...
Finally, the only way today to produce an EMP strong enough to knock out the equipment in a car is a nuclear explosion.