Renault has admitted there is "something wrong" at its Viry-Chattilon base.
The French marque is struggling to get to the bottom of a fundamental problem in the area of its piston design that has led to multiple failures in 2015.
"On the dyno the engines are reliable," chief Cyril Abiteboul said, "but when we come on track they are not.
"Obviously there is something wrong in our validation process, from dyno to track. It’s just like aerodynamics, when the wind tunnel is not telling the truth; it’s exactly the same in the engine world," he told F1’s official website.
But the Frenchman said Renault is working hard to solve its problems, and keen to race away from earlier suggestions it might split with Red Bull or even quit F1 altogether.
"We are living through a tough moment," said Abiteboul. But "this marriage has all the reason in the world to last.
"So we have to do a better job on-track, but we also have to a better job off-track," he insisted.