(Reuters) - Formula One teams began their final pre-season test in Bahrain on Thursday with champions Red Bull and engine partners Renault still struggling as Mercedes-powered rivals racked up the laps.
Australian Daniel Ricciardo, Sebastian Vettel's new team mate at Red Bull, started off with a promising 32 laps in the morning but an attempt at a longer run in the afternoon was aborted.
He told reporters that the team were still playing catch up after a difficult first two tests in Spain and Bahrain: "We're definitely not up to scratch with where we'd like to be in terms of programme," he said.
"It's clear we probably won't come out to Melbourne and dominate as the team did last year, but it's still very early to say. We're getting there. The morning was definitely better and we definitely made a step forward in terms of power."
With the season starting in Australia on March 16, the four Mercedes-powered teams - Mercedes, McLaren, Force India and Williams - have looked well ahead of the four using Renault engines.
The works Mercedes team of Lewis Hamilton and Nico Rosberg alone completed 3,073 km over the first eight days of testing in Spain and Bahrain while the four Renault teams together managed only 4,019 km.
The Red Bull spent much of the afternoon in the garage before Ricciardo, who has replaced compatriot Mark Webber, managed seven more laps.
Red Bull's race engineering coordinator Andy Damerum said the afternoon run had been cut short when the sensors reported some issues that turned out to be a problem with the exhaust.
Mercedes teams were the only ones to have carried out race simulations before the final test with four times world champion Vettel's Red Bull risking heading for Melbourne without having gone a full race distance in one stint.
Mexican Sergio Perez, in a Mercedes-powered Force India, was quickest on Thursday with a time of one minute 35.290 seconds ahead of Valtteri Bottas in a Williams, also powered by the German unit.
Bottas put down the most mileage, 128 laps of the 5.412km circuit compared to Perez's 105, with a race simulation in the afternoon as well as tyre work for Pirelli without any issues.
McLaren rookie Kevin Magnussen also had a productive day in his Mercedes-powered car with 109 laps, including a full race distance, and the sixth best time.
Ferrari had Kimi Raikkonen third on the timesheets, with 54 laps under his belt.
The Renault teams filled four of the bottom five places with a total of 145 laps between them compared to 431 for Mercedes rivals.
Japan's Kamui Kobayashi did the fewest (19) in the Caterham while Venezuelan Pastor Maldonado, who left Williams at the end of last year, managed only 31 for Lotus after being sidelined by problems with a new specification exhaust.
"It wasn't what we wanted today but we are all working very hard to make progress and I'm sure we'll have solutions quite soon as a team," said Maldonado. "It's clear we have good potential and the car is not bad."
Renault F1 deputy managing director Rob White had said after last week's test that the manufacturer had made progress but were some weeks behind where they had wanted to be.
"We are not back on schedule but we are moving in the right direction," he had said, adding that the team at the Viry factory was "working night and day to solve our problems."
(Reporting by Alan Baldwin, editing by Justin Palmer)