Williams technical director Sam Michael admitted that the team needed more mileage to get through its setup program after a disrupted test at Catalunya today.
Most of the morning's running was on a damp track following heavy rain earlier in the week, and Rubens Barrichello was then sidelined for much of the afternoon while a precautionary engine change was carried out.
"We didn't have enough setup time today," said Michael. "The track was moist to start and didn't start ramping up until late morning, at which point we encountered an issue with the engine. Over the break, we changed the engine and did just one proper run at the end of the session."
But he said the day had not been a complete write-off.
"Despite the downtime, we actually tested and measured quite a few aero and systems items in the background," said Michael, who added that the team would use KERS again tomorrow, having deactivated the device for the end of the Jerez test and today following glitches last week.
Barrichello said the mileage on a damp track this morning had still been handy.
"We did some laps in the wet this morning which was good as it allowed us to get a feel for the car on intermediate tires," he said. "Unfortunately, we didn't get much running in the dry."