Williams will decide tomorrow whether or not to race a new exhaust system the team ran in free practice on Friday in China.
Rubens Barrichello, who ended the day 16th fastest, ran the exhaust on his car in the second session but the results of the test proved inconclusive.
"They seemed to lose a little bit of performance toward the end of the last session, though, which means we'll have to work hard to evaluate them properly," said the Brazilian. "We need to go through the data to see whether we will keep to this plan or go back to the original one."
The team's technical director, Sam Michael, added: "We had some issues with the new exhaust system we're running on Rubens' FW33 in the second session. We'll now review the data to decide whether or not to race it.
"That aside, we covered good mileage on the option tire which has given us some solid data for the race. We will also fit new engines in both cars for tomorrow."
Barrichello's teammate Pastor Maldonado reported himself happy with his first day's running on the Shanghai circuit.
"Today went well and we've learned a lot," he said. "I did lots of miles which is useful because this is my first time at this circuit. The car felt good, especially on the long runs in P2. We don't know where the others are or what fuel they're running, but I think we're looking better here than we were in Malaysia."