By Andy Pasztor The National Aeronautics and Space Administration has determined that sensors flagged problems with two out of four main engines of a mammoth deep-space rocket during a key ground test that ended prematurely over the weekend. But a spokeswoman for NASA on Tuesday said preliminary findings indicated the cause of the difficulties likely stemmed from how the test was set up for the Space Launch System booster designed by Boeing Co., rather than malfunctions or defects with the engines themselves. Responding to questions about the cause of Saturday's premature engine shutdowns--which occurred about a minute into what was supposed to be an eight-minute test--agency spokeswoman Kathryn Hambleton said all of the engines performed as expected before the abrupt automated shutoff.