MHR Fund Management LLC said Friday (June 15) it has a 13.6% stake in Navistar International Inc., making it the largest shareholder in the U.S. truck and engine maker, and putting it ahead of the 11.9% stake of investor Carl Icahn.

Reuters reported that MHR, founded by Mark Rachesky, a former associate of activist investor Icahn, now holds 9.4 million shares in the troubled company, bought May 22 through June 13, it said in a filing with the U.S. Securities and Exchange Commission (SEC).

That makes it the biggest investor in Navistar, based on current Reuters data.

Navistar shares leapt 11.2% to $30.95 in early trading Friday on the New York Stock Exchange.

MHR built its position as Navistar hit fresh three-year lows in the wake of an unexpected quarterly loss, and news that a U.S. appeals court would no longer allow it to pay fines to get around curbs on selling diesel truck engines that don’t meet U.S. pollution standards.

In the filing, New York-based MHR said it “may seek to engage in discussions with (the) management and others concerning the business and operations of the company.”

Navistar declined to comment on the news. Rachesky wasn’t immediately available to comment.

Rachesky, who worked for billionaire investor Carl Icahn before co-founding MHR, has previously invested in Lions Gate Entertainment Corp. He is also the chairman of Leap Wireless International Inc.

Last week, Icahn raised his stake in Navistar to 11.9% from about 10%, taking advantage of a sharp drop in the stock price triggered by weak results.

Trading in Navistar shares has been volatile over the past two weeks, plunging as much as 28% on June 7 after news of the quarterly loss, then recovering a day later when Icahn raised his stake, and after Fiat Industrial Chairman Sergio Marchionne hinted he was keen on the company.