[Christ]

If you have a manual, try keying off while braking down a hill. You won't lose p/s or brakes. If auto, try interrupting the injector circuit, and sitting them off manually while decelerating. If you don't physically feel a difference in engine drag, you're already in dfco.

Your LED may be lying, also. If you wired it to check for power, there's a good chance that it is. Most injection systems pulse/switch the ground side of the circuit (ecm input), with a constant power feed, often from some kind of distribution center.