Italy's Autosprint said Lotus was unable to use the unit two weeks ago due to "other technical difficulties" with the troubled E22 car.
Lotus is planning even more significant improvements for the start of the European season in Barcelona next month, but team driver Romain Grosjean is cautious.
"In F1 there are no miracles, only work," the Frenchman is quoted by RMC Sport in Shanghai.
"We will not be on pole in Barcelona: maybe we will be better, maybe we will take a more important step than we would at other times," he added.
Also marching forward after the depth of Renault's winter crisis is reigning world champion team Red Bull, who according to Autosprint have been taking delivery of box after box of new parts in the Shanghai paddock.
Sebastian Vettel, however, expects Mercedes to still be clearly ahead in China.
"Certainly it would be a huge surprise if we have already closed a gap of about one second per lap," said the world champion. "It's better to be realistic, and realistically we can be in the top five."
And after four consecutive world titles, Red Bull's pace is not German Vettel's only problem. The other is sitting at the wheel of the sister RB10.
"I'm happy for him," Vettel, referring to his new teammate Daniel Ricciardo who according to some has had the performance edge so far in 2014, said.
"It's nice to see that he is pushing to the maximum and it's always good to have a reference," he added.