Why is my engine misfiring?

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! A P0303 code and a stubborn misfire in cylinder 3 even after swapping out the ignition coil, plugs, and wires? Your F-150 is keeping you on your toes. Since the usual suspects have been checked off, let's explore some other possibilities. First, let's consider the fuel system. A clogged or faulty fuel injector can cause misfires. Try cleaning or replacing the injector for cylinder 3. Next, a vacuum leak around that cylinder can mess with the air-fuel mixture, so give those hoses a thorough inspection. Check the intake manifold for cracks or leaks as well. Also, don’t overlook the mechanical aspects. A compression test can reveal issues like a worn valve or piston ring, which can cause misfiring, especially at lower RPMs. One last thought: make sure the plug is tight, and the coil is working properly. Sometimes, parts can be bad right outta the box! If you need any further advice or if you'd like any help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554.