No. Think of it this way: every liter of fuel that is expended can propel a ship a certain distance. Reducing that intake will make your movement slower, and while you will *technically* use less fuel in that time tick since you aren't moving as far as you could, it doesn't actually improve efficiency per unit of distance travelled. When you reach your destination, you will have used the same amount of fuel; it just will take you that much longer to arrive.
If you wish to have efficient engines, then you must design them that way from the outset.