The light came on today. Had Advance pull the code. Exact Reading was: Very Small vacuum leak in Emissions system. Then I noticed Driveability of the truck changed. It idles lower and smoother, and drives better in my opinion. (If I am not mistaken, it may be pulling slighty better gas mileage.) Any comments on this? Any one had a Code like this before?

 

I'm sure a lot of people have had vaccum leaks. Trust me, just get it fixed man. No tellin' what could bad next due to this going bad even though it seems to run better.

 

Check your gas cap, i bet that's it. The very small leak your experiencing is not going to make your truck run better. Kind of like the feeling that your truck runs better after you've washed and waxed it It's either coincedence or your imagination

Tom

 

A loose gas cap allows fuel vapors (hydrocarbons) to evaporate into the atmosphere. That's considered an emissions problem, so your check engine light turns on.

Your car doesn't *exactly* know your gas cap is loose. It just knows that there's a leak in the fuel system somewhere that's letting fuel vapors escape into the atmosphere. More often than not, the fuel cap is the culprit. Either it's loose or the seal is leaking. How does the car know this? It uses a fairly complex test, applying a vacuum to the fuel system and monitoring how long it takes the vacuum to "leak down". On new vehicles, it can detect a hole as small 0.020 of an inch!