(Reuters) - Renault have made some progress in ironing out the engine problems that have blighted Formula One preseason testing, but will head into the season-opener in Melbourne with doubts about "incomplete" preparations.
Renault supplies champions Red Bull, Toro Rosso, Caterham and Lotus, and the performance of their new engine disappointed at the tests in Jerez and Bahrain.
After managing only 151 laps in Spain, Renault-powered cars spent more time on the track in Bahrain but still finished the 2014 tests with less than half the total kilometres of the four Mercedes-powered teams.
Renault were also considerably slower, with four-times world champion Sebastian Vettel's fastest time on Sunday's final day of pre-season testing 4.190 seconds slower than table-topping Lewis Hamilton's best with Mercedes.
"We can't escape the fact that we did not complete the entire programme with all the teams and that some Melbourne preparations are incomplete," Renault Sport F1's deputy managing director Rob White said on the manufacturer's website (www.renaultsportf1.com/).
"On the upside, we have done some of everything, with simulations of qualifying sessions, starts, race distances and long stints and it is fair to say that once again we have made some real progress.
"We have cured or found workarounds for some of the problems we had previously identified. New problems revealed as we ran more have added to the unsolved items, and have disrupted running, which is disappointing for our teams."
Formula One has undergone the biggest technical revolution in more than 20 years, with the introduction of a new turbocharged V6 engine and energy recovery systems.
White said their new 'power unit' remained immature, displaying shortcomings in torque delivery, and suggested the manufacturer would be scrambling to fix the teething problems ahead of the March 16 opener at Melbourne's Albert Park circuit.
"Between now and Melbourne we have a number of items to cover," he said.
"Melbourne will be an anxious weekend. Conducting a normal race weekend, in which both cars run well during each session for every team, would be a great relief.
"I hope we can support our teams and drivers to explore the performance of the car and allow the race to deliver its sporting verdict."