Few days after getting truck back on road engine light came on. Had a random misfire ,o2 sensor locked and the small emission leak p0442. Fixed the intermittent misfire with new plugs and o2 sensor code went away. I can't find the leak in emissions . Truck keeps saying tighten gas cap. I bought a new one and it didn't help. Is there a way to find the leak without a smoke machine? I'd like to stay away from the dealer. Any area I can look at before have to bring it in?