Jenson Button heavily criticised his BAR-Honda team after both cars retired from the Malaysian Grand Prix with engine failure after just three laps.
"Compared to last year, we have made a huge step back in every area it looks like at the moment," said Button, who was third in the championship in 2004.
"It's just not good enough because we're quick - that's the annoying thing. It's very disappointing.
"It's got to change, and I know it's not going to change in a hurry."
Button, who wanted to switch to Williams for this season but was forced to stay at BAR after losing a legal dispute, was especially critical of engine partner Honda, the team's co-owner.
"Engineering an engine to last three laps is not difficult," he said. "It's (about) the whole race."
The failures were especially embarrassing for Honda, because BAR had decided to deliberately retire both cars at the end of the Australian Grand Prix so they could fit fresh engines for Malaysia.
BAR technical director Geoff Willis said: "This was a bitterly disappointing end to our race weekend, particularly since Jenson got such a good start and was easily making places in the early laps.
"The car was handling well and we were confident that our race pace and strategy would bring very good results."