I also live in Commiefornia. If the cap failed the smog test, it sounds like it is not sealing properly. It's confusing trying to do some research, some sources say that fuel tanks need to be vented to allow the fuel to flow to the engine but the caps must be designed to prevent evaporation of the gasoline into our already smoggy skies. So maybe there is a fine balance to the venting which allows the fuel to flow but not evaporate and that is why it failed the pressure test ????

 

The seal failed most likely on the gas cap. The OEM cap sealed well and got rid of the CEL.

 

I remember having to replace my fuel cap (2015 R) but had ordered the incorrect fuel cap from a later model FType and it threw a check engine light. Replacing it with the appropriate cap fixed the issue. Just fyi.

 

I purchased a Stant 10508 and installed it today. It fits perfectly. I have not yet driven the car but I do not see any reason why it should be affected. I examined the seal visibly and it appears to be exactly the same as the original. If there are any driving problems I will report them here. Thank you CPQ100 for researching and publishing this.

 

How did you disconnect the tether for the original gas cap ? It looks like it may just be held by a snap in connector on the hinge to the door but I don't want to pry unless I know.

 

I pried it. There is push in type of connector on the end. It is either stiff rubber or some type of flexible plastic. I did not have much trouble getting it out. The connector is below.

 

That is not quite the same as my tether connector. The shape of the end appears to be the same but mine is attached differently. The end of the flat attachment portion which is furthest away from the cord part has a molded in peg shaped projection from the rear side which is slightly barrel shaped to retain it in a hole in the bracket. The end of the flat part which is closest to the cord has a small hole in it through which a plastic compound pin is inserted. The pin is composed of an hollow outer portion which is inserted first and a solid center piece which is then inserted to lock it in place. This is the construction of both my 2018 F-Type and my 2015 XF. I was able to remove the small plastic pin from my F-Type by prying with two screw drivers but the XF was much more difficult and I broke the pin.. Fortunately, it didn't matter since I was moving the cap from my F-Type to the XF because the tether cord had broken on it. The F-Type is not now tethered but that doesn't matter to me.
The photograph of yours appears to show only a single retaining pin and it appears to be of the two part construction like the one in my cars. I could not remove the center insert and when I examined its construction I believe that it is intended that it not be removable. I can only suggest that you carefully attempt to remove the pin, in the knowledge that if you are using the Stant locking cap you cannot use the tether anyway.

 

Mine is also a 2018 - May 2017 build. I took another look at my connector. There is indeed a plastic pin in it which is the smaller of the two in the photo. The pin on mine came out whole when I pried it off. I never realized it before but it possible to take the pin out of the tether. I just did it.

 

It looks like one of those plastic expandable fasteners that you push into a hole and then push the center pin in which expands the outer pin diameter. I'll try to carefully pry it out, if that fails I'm sure it can be drilled out and replaced with a new one if for some reason I decide to put the original cap back on. Those expandable fasteners are available at most auto parts stores and are inexpensive.

 

A follow up: I installed the Stant 10508 locking gas cap and went for a short drive. No issues with a CEL coming on but I'll keep the OEM cap in the car until I go through a tankful of gas just to make sure that there are no issues.

I removed the tether by working a small flat blade screwdriver under the end that attaches to the gas door hinge and gently working it and prying upwards. If you are going to attempt it one of those plastic tools that are made to remove automotive interior trim might be better. I did manage to gouge up the plastic on the hinge a little bit but was able to sand it out. The fastener that is visible on the exterior of the tether anchor point should be able to be reused, I pushed the center pin that expands it back out so if I ever want to reinstall the original cap and tether it should be a 5 second job.

 

watching.....