Grosjean scored Haas's first points since June with 10th at Austin, but a week later in Mexico he qualified on the back row of the grid and described the situation as "unacceptable".

The Franco-Swiss remained unhappy with his brakes, despite Haas trying a new brake material from supplier Brembo, and was baffled by a handling imbalance.

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Haas changed his floor to an older specification on Saturday evening but that didn't solve the problem and Grosjean ended the race an anonymous 20th, one place behind team-mate Esteban Gutierrez.

"I don't know what happened this weekend," said Grosjean.

"We tried to change a few parts to analyse what was going wrong but we didn't find the problem.

"The car was just nowhere in the race so it was very difficult to handle, to drive - we got nothing right."

When asked what he felt the problem was, Grosjean replied: "Inconsistency. Understeer, oversteer, you never know what you're going to get.

"The car is pulling on the left on braking.

"I don't know, it feels like something weird - the car was just not behaving the way it should."

Gutierrez described his home race as the American team's worst of its debut season and while he conceded Haas does not yet know why, he believes it knows in which direction it needs to push.

"We dropped pretty much in the last couple of races and we have to work as a team to get back to where we were," Gutierrez said.

"There has been a lot of ups and downs, but this was definitely the worst weekend that we have had so far in terms of performance.

"But we have to keep fighting and accept what happened, optimise it and do the best we can.

"We had some nice discussions to really understand it and now the engineers have a good direction to try to understand why this happened."

Gunther Steiner said Haas was "all over the place" but is confident the team can turn things around.

"We know what's wrong, we cannot find the balance," said the Haas team boss.

"We were out of the tyre window, we just didn't perform this weekend.

"We have to be honest with ourselves to get better, we have to say we didn't do a good job this weekend, starting on Friday.

"You saw our qualifying, it was appalling almost but you have these days in racing so we just need to get our act together now for the next two races.

"We know we can do it, we got into Q3 two races ago so it's like where did it all go? I don't know."

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