Hello all. New member here I bought a new to me 2007 4 door JK 3 weeks ago. Previous owner of a yj. Anyhow I bought it for a bargain due to a check engine light on and a fuel cap loose message. I had two codes.
The codes referred to
‐ EVAP PURGE SYSTEM SMALL LEAK
‐ LOOSE FUEL CAP
. I just wanted to share what I did to fix it ( thought it might help some others). After much research I decided to start with cleaning the fuel cap o-ring which didn't work. Step two I ordered and replaced the fuel cap to no avail. So I took a good look at all of the evap tubing from the the engine side all the the way to the evap canister and found the battery rubbing the lines and had left a two small rub marks. It didn't look like it was all the way through. I decided to adjust the lines and wrap the tube with a little electrical tape. I gave this a week to see if it would fix the problem however it did not. Next up I decided to change the white sensor on the evap canister. So I swapped out the sensor with a new o-ring ( which was green by the way) and was very hopefully this was the fix. However the codes still remained. At this point I was a a loss of what to do next. After thinking about to for a while I decided to clean the O-ring on the fuel cap again. This time I whiped out the inside of the fuel tube and the o-ring and fired the jeep up. Instantly the gas cap message went away and I just about did a back flip. Fast forward to the next day I went out to my jeep and started it up and guess what. Gas cap loose message again. Once again I put on the thinking cap and decided to put some vasoline on the gas cap to make a better seal and the message went away. So I decided to clear the check engine light. It's been two weeks without any errors so Im confident that my problem has been fixed. PO had stated that he had the check engine light on for the entire time he owned the Jeep and that the fuel cap loose message for the last 6 months. I hope this will be helpful to others with the similar problems.

 

So the new gascap didn't work alone, only together with the vaseline ??

 

Vaseline sucks as temperatures increase. You may have better luck with pure silicone grease. It's available in pool supply stores for greasing o-rings.

 

I believe it was a combination of the new cap cleaning the fuel inlet and the Vaseline. However The old cap may have worked with Vaseline.

 

Thanks for the tip I will try that.