Haas' early-season promise continued to fade in Baku.
Despite targeting fourth in the constructors' championship this year with the initially fast 2019 car, the American team struggled once again in Sunday's race.
Kevin Magnussen started and finished 13th.
"There's not much to say. We were just not fast enough and we have to change it," he told Ekstra Bladet newspaper.
"This is the fourth race in a row that it has happened," Magnussen added. "Ok, Australia was a good result but in the race we didn't actually have the pace."
Haas is working on figuring out the problem, but it is related to getting the more sensitive Pirelli tyres for 2019 into the right 'window'.
"It's something we are really struggling with so we have to find the reason," said Magnussen.
"We hope things turn around in Barcelona. We were good there in the winter tests and we have a lot of data, but the temperatures will of course be different."