One of the most logical ways to save gasoline is not to use any at all. That’s the thinking behind Chrysler’s Interactive Decel Fuel Shut Off, or iDFSO, which turns off the fuel supply when it isn’t needed.

Many automakers use similar technology in their vehicles. Chrysler puts it on a number of engines in its Chrysler, Dodge, Ram and Jeep brands, on both V6 and V8 configurations.

Engines run when gasoline vapour is injected in and then exploded by the spark plug. The resulting energy moves pistons, which turn a central crankshaft; that shaft’s spinning motion is transferred through the transmission and drive shafts to turn the vehicle’s wheels. The crankshaft revolves at all times when the engine is running, but when you’re decelerating, the vehicle’s momentum is enough to keep it spinning. Since the engine is capable of running without gasoline due to this momentum, iDFSO temporarily shuts off the fuel supply.


“When you come off the throttle, the accelerator pedal sends a signal to the engine control unit,” says Nick Cappa, public relations manager for Chrysler Group LLC. “The unit is also taking input from the wheel speed sensors, not just from the pedal, because if you stopped at a stoplight (without fuel supply), the engine would die. If it gets too slow, the control unit recognizes it and the engine goes into normal fuel delivery operation.”

The system is seamless and goes unnoticed by the driver. Fuel is only cut off during vehicle slowdown, either when the driver takes her foot off the throttle or applies the brakes; fuel delivery remains at normal levels during all other driving. While the engine isn’t receiving fuel during the shut-off period, it is still operating normally, and so peripherals such as the water pump and power brakes continue to function normally.

The system is always monitoring the engine’s operation, Cappa says. “It’s always going to pay attention to the speed of the vehicle. It’s just calibration and sensor input only, not a different fuel pump or injectors.”

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