March 13 (Reuters) - The following are the top stories in the Wall Street Journal. Reuters has not verified these stories and does not vouch for their accuracy.
* General Motors Co said it may have known about problems with its ignition switches dating back to 2001 when it was developing but had not yet launched the Saturn Ion. ()
* U.S. investigators suspect that Malaysia Airlines Flight 370 stayed in the air for about four hours past the time it reached its last confirmed location, according to two people familiar with the details, raising the possibility that the plane could have flown on for hundreds of additional miles under conditions that remain murky. ()
* The U.S. launched a last-ditch effort Wednesday to avert a potentially costly diplomatic crisis with Moscow ahead of a vote Sunday in Crimea on whether the region should leave Ukraine and return to Russia. ()
* The Federal Reserve examined a key foreign-exchange benchmark months before global regulators sounded the alarm about potential manipulation, but officials took no public action. ()
* Game maker King Digital Entertainment Plc is planning to start trading this month on the New York Stock Exchange-valuing itself Wednesday at as much as $7.6 billion after it set a price range for its initial public offering. ()
* The U.S. could suffer a coast-to-coast blackout if saboteurs knocked out just nine of the country's 55,000 electric-transmission substations on a scorching summer day, according to a previously unreported federal analysis. ()
* The Federal Trade Commission opened an investigation into Herbalife Ltd, the maker of nutritional supplements that has spent more than a year battling hedge fund manager William Ackman over allegations it is a pyramid scheme. ()
* Purdue Pharma LP says it plans to submit its extended-release hydrocodone drug to the Food and Drug Administration later this year. The company's tablets are designed to prevent users from crushing them for snorting or injection. Shares of rival Zogenix Inc plunged more than 20 percent after the announcement, which appears to jeopardize sales of the company's just-launched drug Zohydro. ()
* Energy XXI Ltd agreed to acquire EPL Oil & Gas Inc in a $1.53 billion cash-and-stock deal that will create the largest publicly traded oil-and-gas producer in the shallow waters of the U.S. Gulf of Mexico. ()
* A former Credit Suisse banker, Andreas Bachmann, pleaded guilty to helping Americans hide money in Switzerland and agreed to cooperate with the U.S. government. ()