Alright guys, about a month ago I got the wonderful little CEL and GASCAP in the odometer. Since then, I've been experiencing the best MPGs I've ever gotten out of the truck. Before the CEL I was averaging 14-15 MPG and now I'm averaging 17-19 MPG. The problem is a cracked vent tube, but I'm tempted to just leave it be because of the improved mileage. Are there going to be any adverse effects caused by the vent tube crack or is it okay to just leave it be?

 

how can it possibly be enhancing your mpg other than your truck thinking you have a vapor leak out of the tube? Maybe the PCM leaned out your A/F ratio but I doubt it. Any power loss?

 

+1 the CEL is probably throwing a code for a bad O2 sensor.. it may be giving information the the engine is running richer than it actually is, making the injection system compensate with less fuel.. be careful because if it fails completely the truck might not want to start or it'll get too lean :S