Romain Grosjean was frustrated after yet another Renault engine problem cost Lotus track time in Bahrain.
Taking over from team-mate Pastor Maldonado on Wednesday, Grosjean managed just 16 laps before an issue with his Renault engine put paid to his running.
It was the second time in as many days that a problem with the engine curtailed Lotus' test as on Tuesday Maldonado also covered only 16 laps.
"I have to say that these two days have been quite tough on all of us," Grosjean told Crash.net. "We were hoping for more, but again they say China or Barcelona will be a good step forward. Let's see.
"I think we are already quite a long way behind. With a perfect qualifying lap you're 16th on the grid which is not where we want to be.
"Today we did some aero tests with hopefully some good results that we can understand for China, a few things that we can maybe redesign, and then we just have to believe that Renault will be capable of bringing better performance and reliability because today was just not acceptable."
The Frenchman's best time for the day, a 1:43.732, was well off the pace, almost 10 seconds behind the Mercedes of Lewis Hamilton.
"We struggled with the power unit all day long, never got the power we wanted and only managed a few laps," Grosjean added.
"We fortunately did some aero laps and got some little information but compared to the programme we had planned today it's far from being done.
"It's been a different problem. Yesterday I was not aware of everything that was happening but today we had a problem with engine from the beginning of the day and then some more problems came on top of it and that was the day. Everything was engine today."
Gallery: Bahrain Test Day Two