Toyota officials have been surprised by the number of engine failures at Las Vegas this weekend and remain unsure of having fully solved the issues that caused five cars to change units before the race.
Polesitter Kyle Busch, David Reutimann, Marcos Ambrose, Brian Vickers and Scott Speed all faced engine issues during Friday's practice session and will all drop to the back of the field for Sunday's Sprint Cup race following engine changes.
Busch's engine is built by Joe Gibbs Racing and his problem was different to the one on the other four powerplants, which are all built at the same shop at Toyota Racing Development in Costa Mesa, California.
Toyota's Lee White said they have identified the area of the engine where the problem is, but they're not exactly sure of what is causing it.
"It's a wear issue between the camshaft and lifter," White said. "It's either a coating, lubrication, lack of lubrication, too much lubrication, not enough coating or a material situation or just the simple fact that we haven't been testing."
Last week Fontana polesitter Brian Vickers faced the same problem and was forced to change his engine and thus lose his pole position start. White said they made changes for this weekend hoping to cure the problem but admitted they actually made it worse.
"We thought [the change] was the right direction," White said. "I'm disturbed to say that the right direction apparently was the wrong direction. We came here and thought we had a handle on it. We didn't. We made it worse."
White said they have made further changes to the engines at Las Vegas while trying to prevent a repeat of what they saw on Friday. However those modifications are expected to bring power down on those units fitted to the cars that were forced to make the switch before qualifying.
"The adjustments we've made are four or five horsepower, but that's not insignificant," White added. "No driver would give that up willingly. Our goal right now is to give them the best shot to get to the end [of the race]."
Toyota has not been the only manufacturer facing engine issues this season. Last weekend at California four Chevy R7 engines failed during the race, two from Hendrick Motorsports and two from Earnhardt Childress Racing Engines.