(Reuters) - Renault recognised they faced a "litany of issues" with their new Formula One engine on Friday after problems forced champions Red Bull to end the first pre-season test early and with barely any laps completed.
The dominant team of the last four years packed up and headed for home as Renault voiced their determination to make amends for failure at the next track outing in Bahrain in two weeks' time.
The problems affected all three Renault-powered teams testing at the Jerez circuit in southern Spain and Renault Sport F1's deputy managing director Rob White said they had a large job list to tackle.
"We have not run enough laps, and when we have they have not been run at an acceptable performance level," he said in a statement after a test that saw Mercedes and Ferrari-powered rivals lapping with far fewer problems.
Formula One has a new 'power unit' - a 1.6 litre V6 turbo with complex energy recovery systems - this season, replacing the tried and tested 2.4-litre V8 engines.
"We are very frustrated to face this litany of issues that we should have ironed out on the dyno (test bed) and which have deprived us of a precious learning opportunity," added White.
The Briton said that, despite appearances, useful progress had been made, no big new fundamental problems had emerged and that Renault had the necessary tools and determination to succeed.
"The step we must take to reach an acceptable level of in-car performance is bigger than we would have liked. It is unacceptable that we have not been able to mitigate the problems sufficiently to allow our partners to run at any length," White explained.
"We are working hard to correct this in time for Bahrain and aim to make amends there."
Red Bull managed only 21 laps over the four days, out of a total of 1,470 completed. Mercedes driver Nico Rosberg did 188 on his own, including a full race simulation, compared to quadruple world champion Sebastian Vettel's 11.
Mercedes-powered cars accounted for 875 laps, to Ferrari's 444 and Renault's 151.
Brazilian Felipe Massa, in a Mercedes-powered Williams, was fastest on Friday with Danish rookie Kevin Magnussen's best time for McLaren Mercedes on Thursday remaining the quickest lap of the test.
Vettel won 13 races in 2013 including the last nine but his chances of a 10th in a row when the season starts in Melbourne on March 16 are looking far less likely.
The champions said continuing problems with the new RB10 car, unveiled only on Tuesday, had forced them to stop with Australian Daniel Ricciardo managing to get just seven laps in on Friday.
He ended up 11th and bottom of the day's timesheets.
"It's been a very difficult test," said principal Christian Horner. "We have had numerous Renault issues as well as chassis cooling issues, which have affected our progress.
"However, despite the lack of mileage, what we have managed to learn shows that the problems should be solvable for the next test in Bahrain."
Red Bull's race engineering co-ordinator Andy Damerum said they had made improvements as they went along on Friday morning.
"However, we then discovered a mechanical issue with the car and after investigation it became clear we would not be able to fix this in time to run in the afternoon, so the decision was taken to retire early.
"Two weeks is a long time in Formula One and we, and I'm sure Renault, will work flat out now to solve the problems we've been having," he said.
(Editing by Ed Osmond)