MELBOURNE, Australia - Renault has made some progress in ironing out the engine problems that have blighted Formula 1 pre-season testing but will head into the season-opener in Melbourne with doubts about "incomplete" preparations.Renault supplies Red Bull, Toro Rosso, Caterham and Lotus but the performance of its new engines disappointed at the tests in Jerez and Bahrain.After 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.'INCOMPLETE PREPARATIONS'Renault was also considerably slower, with four-times F1 champion Sebastian Vettel's fastest time on Sunday's final day of pre-season testing 4.190sec slower than table-topping Lewis Hamilton's best with Mercedes.Renault Sport F1's deputy managing director Rob White said on the manufacturer's website: "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."On the up side, we've 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've cured or found workarounds for some problems. New ones were revealed as we ran and disrupted running, which was disappointing for our teams."F1 has undergone the biggest technical revolution in more than 20 years with the introduction of a turbocharged V6 engine and energy recovery systems.'NUMBER OF ITEMS TO CHECK'White said Renault's 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." Stay with Wheels24 for the 2014 F1 season – fresh reports every day.