Toro Rosso driver Pierre Gasly says the Honda engine is not solely to blame for the team's lack of performance in the previous two Formula 1 races.
The Faenza squad starred in the second round of the season, with Gasly scoring a sensational fourth place in the team's second race with engine partner Honda.
Toro Rosso was unable to replicate that kind of performance in the next two events, however, struggling near the back in China and last weekend in Azerbaijan.
Gasly said the team has been unable to understand the slump after such a strong showing in Bahrain, but admitted the Honda engine was only one part of the problem.
"It's difficult, really, because the last two weekends have been really tough in terms of performance," said the Frenchman. "We knew that China has one of the longest straights of the season, Baku as well.
"Even on the chassis side we are not so competitive. We seem to be competitive under braking but then all the traction fades. We don't really have the pace. It's something that we need to understand.
"I don't understand how it's possible to be so competitive, have a car that is that good there balance-wise, also in terms of potential, and then to have such a big delta as soon as you go to another track."
Teammate Brendon Hartley said he was also failing to understand why Toro Rosso has struggled.
"I don't know. I wish I knew," he said. "The obvious question is why were so quick in Bahrain. OK, Pierre had the result. I also had the pace in Bahrain, but obviously I didn't get the result.
"Right at this very moment I don't have the answers and I think the team will continue trying to understand. But yeah, it was only a few weeks ago," added the Kiwi, who scored his first point in Formula 1 with a 10th-place finish in Baku.
Gasly said after the race that the power unit's energy management had been "quite difficult" for the team.
Honda boss Toyoharu Tanabe conceded the Japanese manufacturer needed to find solutions for its lack of performance.
"We had a difficult weekend again," said Tanabe. "Pace in qualifying maybe – especially Gasly's car – was not too bad. The position was bad because of the accident. Our pace during the race was not good enough. We need to analyse that.
"We need to analyse data and then find out what happened. We had a lot of passing during the race. Energy management side and PU performance, we need to analyse."
Additional reporting by Oleg Karpov