Misfire forces Williams to change engine settings in Spa qualifying

Felipe Massa's engine was misfiring on his first run in Q1 so Williams switched it, and Valtteri Bottas' unit, from qualifying to race mode for the remainder of the session.

As a result, it abandoned plans to attempt to do its best lap on the softs in Q2 so it could focus on ensuring it made it into Q3, with Bottas ending up eighth and Massa 10th.

Both drivers will start the race on the super-softs, which according to Pirelli's recommendations will require them to stop before the tyres have done nine laps in total.

"It's the power unit software, the settings, which we are currently investigating the exact details of what happened," said Williams performance chief Rob Smedley.

"It is probably just to do with the way our power unit engineers have set it up and that has given us the issues that we have had.

"It's finger trouble basically, you can have this type of problem when or wherever.

"The result was on the first timed lap, when we put the qualifying mode in, we had horrendous misfires all the way from Turn 1 down to Turn 4. That was with Felipe's car.

"We understood there was an issue with the qualifying mode so we knocked that mode back into race mode and he finished his first lap for the latter part of that lap, he finished that in race mode.

"Even in race mode, we were suffering with misfires with the way the engines have been set up so we must try and get that sorted for tomorrow."

Bottas believes Williams could have outqualified Force India's Sergio Perez and Nico Hulkenberg, who finished sixth and seventh, without the problem.

"We couldn't run the best mode and that cost us about three tenths," said the Finn. "From our calculations, I think we could have [beaten Force India].

"Our race pace here has looked very promising. If the temperatures get any cooler, it's only going to help us."

Massa is hopeful of his team's chances of beating Force India, which it is battling for fourth in the constructors' championship.

"I'm very confident we can fight with Force India, but we know that the race will be difficult," he said.

Perez said Force India's focus will be maximising the best result of both cars rather than its battle with Williams.

"As a team we must make sure that we maximise the potential with both cars," he said. "We might find ourselves in a position where we have to do something difficult with one of the cars but that will always be in the benefit of the team.

"I am ready for that, and I am ready to help the team get fourth place.

"We are not really concerned about Williams, we are basically focusing on ourselves, making sure we are maximising everything and tomorrow will be an important race for the championship battle."