Discovery's tiny fuel leak has been stopped but not fixed, and officials at Cape Canaveral have decided to test-fire the ship's three main engines before deciding whether to remove the space shuttle from the launch pad for repairs. While preparing for that test July 28, engineers will decide if there is a way to fix the leak on the pad, whether the leak can be isolated from the fuel system or if it is so insignificant that is does not pose a flight hazard if left as is. If Discovery has to be rolled back to a hangar, its planned launch as the first post-Challenger shuttle flight would be delayed up to two months. The flight-readiness firing of the three engines already has been delayed two days, so even if the shuttle stays on the pad, there likely will be a delay of at least a few days of the Sept. 6 launch target date. By going ahead with the test-firing, shuttle managers hope to minimize lost time if Discovery has to be taken off the pad.