The Federal Reserve is about to throw some more fuel on the fire it has been stoking for more than two years. But the expected move to pump more cash into the system might not do much good at this point, and the economy could get burned in the process. The central bank has pumped about $2 trillion into the economy since the recession began in September 2008, in a process known as quantitative easing — massive purchases of financial assets, like mortgages and Treasurys, designed to encourage spending through lower interest rates. Now, as the Fed prepares for a two day meeting the first week of November, top officials are sending clear signals that more purchases are on the way.