If you’re shopping for a used GM V8, this is one system you don’t want to ignore. GM’s AFM (Active Fuel Management) / DOD (Displacement on Demand) system was designed to improve fuel economy by shutting down four cylinders during light driving. Sounds great on paper—but over time, those specialized components can become a costly problem. Lifter failures, camshaft wear, misfires, and expensive repairs are all issues that have been linked to these systems. Before you buy, know what you’re looking