Williams drivers Pastor Maldonado and Valtteri Bottas admit that the team have significant work to do after practice for the Malaysian Grand Prix.
Maldonado was only sixteenth in FP2, with Bottas three places further back.
"We didn’t have the pace today unfortunately," said Maldonado.
"We need to analyse the data tonight to see what we can do. We have a lot of work to do but we’ll be pushing hard to see what we can achieve tomorrow."
"We had a number of parts to test today following the race in Melbourne and we were evaluating different things between the two cars," added Bottas.
"We will analyse the data to see what worked well and make some decisions for qualifying tomorrow. We hope to find some improvements, but we know we still have a lot of work to do to close the gap."
Technical director Mike Coughlan suggested that the team is already looking to the next race in China.
"We haven’t made the progress we had hoped for today. We need to look at the data we have from both sessions to maximise the package we have. We will then head straight back to the factory to work on some improvements ahead of Shanghai," he said.