Helped by a lightened debt load, Ford Motor Co. posted a surprise second-quarter profit of $2.3 billion Thursday, following the worst loss in company history a year earlier. Shares rose 10 percent in afternoon trading. The net profit ends a string of four straight quarterly losses for the nation's second-largest automaker, which has gained US market share at the expense of cross-town rivals Chrysler Group LLC and General Motors Co., both of which spent time under bankruptcy court supervision. Ford last went into the black in the first quarter of 2008, with net profit of $70 million. However, excluding its debt reduction and other items, Dearborn, Michigan-based Ford would have reported a quarterly loss, though smaller than Wall Street expected. Chief Financial Officer Lewis Booth said the improved second-quarter results are a sign that the company's cost cuts and emphasis on new products are paying off. He stuck to Ford's earlier prediction that it would return to annual profitability in 2011. “We're 18 months away, I guess,” he told reporters on Thursday, adding that a full year of profitability hinges on improved auto sales in the US and Europe. Unlike GM and Chrysler, Ford avoided bankruptcy and government loans, mainly by borrowing or setting up credit lines totaling $23.5 billion in 2006 and 2007 to prepare for an economic downturn. Since then the company has cut costs and rolled out new vehicles, mitigating its sales decline in the worst auto sales market in more than a quarter