in a gas engine all you have to do is take off the vacum line to the brake booster and stick the hose in the can and let the engine suck about 1/3 of the can in. then turn off teh car and let sit and restart and your good. on a diesel you can pour the whole can into the tank or fill the whole fuel bowl up with it. i usally do this when i change out my filter. its really good stuff.