Daniel Ricciardo says the Renault Formula 1 engine in his Red Bull was "bleeding" power in qualifying for the Japanese Grand Prix, meaning sixth was the best he could do.
The Australian, who will start fifth thanks to Sebastian Vettel's three-place grid penalty, felt the problem cost him at least a tenth of a second.
Ricciardo said he has suffered from the problem in previous race weekends but team-mate Max Verstappen, who qualified six-hundredths of a second faster, did not have the same issue.
"I was losing straightline speed," said Ricciardo.
"It's not the first time, we saw signs of it last week and it had a bigger effect this week.
"It's just a bit frustrating because you see the overlay [with Verstappen], you see I'm doing pretty good in the corners and just bleeding on the straights.
"We all want the same for both us but it's just sometimes luck of the draw."
Ricciardo is due to get a new engine for the next race at Austin, but is unsure if the mileage of his current power unit is contributing to the problem.
"Normally you don't see a deg in the engines, they hold pretty well for the life they are supposed to do," he said.
"But it was there last week, I didn't bring it up but it's been there a few times this year."
Ricciardo is confident the problem won't have such an impact in the race tomorrow, when engines aren't running at maximum power.
"Once we start running a bit more conservative in the race, the deficit becomes less," he said.
"I don't expect it to be as much tomorrow. If it is I will just drive harder.
"I hate making excuses but that's just how it was today, unfortunately."
He added he is confident of finishing on the podium, whether the race is held in wet or dry conditions.
"Our long run pace yesterday was really solid and even though we didn't qualify as far up as we would've liked, I'm still confident we can somehow find a way through tomorrow," said Ricciardo.
"But if it's wet then I think we will have a really strong car."
Verstappen had a gear synch problem in qualifying, but this was fixed in time for his final run.
He added that the pace of the Ferraris, with Kimi Raikkonen and Vettel setting third and fourth fastest times, was not a surprise.
"The whole weekend they've been strong, and I knew before qualifying it was going to be very close, and it was like that, within a tenth," he said.