Workers were systematically closing valves and watching for pressure buildup that could affect chances of stanching the flow of tens of thousands of barrels of oil that have leaked from the well since April 20.
BP reported engineers were concentrating on repairing a leak in a line that is part of the new device. Until the leak is controlled, the test won't continue.
An explosion on the Deepwater Horizon rig, operated by British oil company BP, in April killed 11 workers and began the oil leak. Since then, estimates indicate, more than 5 million barrels have escaped the wellhead.
Pressure indications will give the engineers clues about the structural integrity of the well itself. Those signs may indicate it is safer to allow the oil to flow. BP added a ship to its collection fleet, giving that aspect of the operation a capacity to capture more than 53,000 barrels of oil a day.
BP is also drilling relief wells. The first of those is said to be a few feet from intersecting the leaking well. A BP release said, "The relief wells remain the sole means to permanently seal and isolate the well."
Operations also continue to clean up the millions of barrels of oil that have fouled the gulf and reached beaches from Texas to Florida. It is unclear how long that oil would continue to affect waters and ecologically sensitive wetlands along the Gulf Coast even after the flow of oil is stopped.