I recently lost my gas cap. I've been driving without it, does this have any effect on performance or gas mileage? (assuming, it doesn't splash around and leak out or anything, seems to be doing fine)

 

You may get a check engine light. I believe the fuel system needs to be under pressure.

 

Yup, just a matter of time before you get a CEL.
Check out your local auto part supplier - an aftermarket replacement should do fine.

 

yea, it needs pressure, its bad for the fuel pump without one, and you gotta have it to pass emmissions here. I suggest buying one with a lock, its not much more and even if you have a locking door, why not have some extra protection?

 

I bought a gas cap today 8$ at carquest. Funny thing is i've been driving it around a lot without a check engine light. I didn't get a locking one, because I live far away from any big cities, and it's not worth the hastle. Also, in michigan we don't have emissions tests that you have to pass (lucky us )

 

I have a gascap that I bought several years ago that doesn't have to be removed to insert the nozzle when filling up your tank. It eliminates the possibility of losing or driving off without your gascap. I believe it was $7 or so from Advance Autoparts.

 

I was in the same situation as ilikesoup and then bought a cap. Same day Check engine light came on. Don't want to spend 60 backs to find out what this means - or should I? I also realized that when I fill up, gas leaks somewhere around filler neck. it's not the tank for sure. Could it be plugged or rusted vent line?
Thanks.

 

Get the code figured out - troubleshooting without the trouble code is going to be as good as random guessing.

 

Ditto, need a code # do make any diagnosis at all.

 

Head to AutoZone, Advance Auto or someplace similar and have them check the code from the CEL. They should be able to and it should be free. If they can't/won't, pick up a Chilton or Haynes manual while you're there and do it yourself. That'll get you going in the right direction.

 

If it is fact a gas cap then if you do pop a code it should clear itself. They work off a 2 trip logic (one trip is from when you turn your veh on to when you turn is off for more than a few mintues). If ya pop a code and find a missing or faulty gas cap and replace it, the warning light should go off after a few. If it doesn't you have something else wrong... Most emission based codes are on a 2 trip logic... And driving around without one will effect your entire evap system, almost everything within this system works off pressure differences and changes