Johnny Mowlem admits the engine problem which blighted the No. 65 Jetalliance Lotus Evora's running on Thursday remains a bit of a mystery.
The issue started as a small vibration when the car was cold, but on Thursday the engine gave way when Mowlem's teammate Jonathan Hirschi was behind the wheel.
"We'd been having strange vibrations on the car from cold anyway," Mowlem explained, "but it would go away after a lap or so. Then Jonathan went out when the car was cold and complained of vibrations. Because they had faded with me the team told him to keep going, and the engine then let go in a big way.
"We believe the vibrations knocked out one of the spark plugs, which fell into the cylinder. It was really disappointing because we missed out on four hours of running, just one day after a fantastic Wednesday when we were really encouraged by our pace on a full tank and used tires.
"I'm still very encouraged with the pace of the car, but these engine issues are not anything that happens on the dyno so we need to get to the bottom of the cause. All the bits individually are fine, but there's some issue in installation – it's a bit of a mystery at the moment."