2007 Ford F15-0 Evaporative Emission System Code P0446 - Smog Failure & Engine Stalling Issue
My 2007 Ford F150 with a 5.4L engine is failing smog inspection due to a persistent OBD2 code P0446: Evaporative Emission System Vent Control Circuit. The check engine light was initially on, and I previously experienced a misfire on cylinder #4. I replaced the coil pack from cylinder #4 to #3, which eliminated the blinking engine light and any misfire codes. However, my truck now struggles to maintain speed—especially when climbing hills—and begins to bog down during acceleration. Despite the absence of misfire codes, the vehicle still fails to perform properly under load. I am using an Innova 3120e OBD-II scanner for diagnostics. I'm at a loss as to what could be causing this sudden performance drop after resolving the misfire issue. Could the P0446 code be directly affecting engine response, or is there another underlying problem? Any insights or troubleshooting steps would be greatly appreciated. Thank you in advance for your help. Bob
Start with basic diagnostics: refer to OBD2 code P0446 at http://www.obd-codes.com/p0446. The key term is 'CIRCUIT'—check for 12V power at the vent valve. With the key off, verify both wires are hot (12V) when the engine is off. For performance issues: check fuel pressure and monitor pressure drop under KOEO (Key Off Engine Off) conditions. Clean the Mass Air Flow (MAF) sensor—avoid using an oiled air filter as it can interfere with readings. If needed, visit an auto parts store for a free OBD2 scan. A second opinion from professionals may help identify hidden issues or wiring faults.