Weird noise coming from gas cap

[jms_brns]

I'm getting a weird humming/vibrating noise from my gas cap that just started happening pretty recently. It happens at 22" and 1:14" into this video that I took:

[video]https://goo.gl/photos/gJG1BJj5zsgUvTSK6[/video]

For some background, its a 1999 Montero that was retired from daily driving about 5 months ago. Since then I take it out about once every week or two for a few miles just to make sure things don't gum up too bad. It has a few issues that I want to start fixing as the bank account and accountant permit. I just had the valve stem seals done by a great mechanic (and fellow forum member??) who was recommended to me by Toasty. The gas cap rattle/hum started a few weeks ago, before the recent work was done.

The obvious place to start is to replace the cap, but I just wanted to post the video in case there could be something else going on that someone here might be aware of. For example, towards the end of the video I remove the cap and it releases quite a bit of pressure, which I don't remember being normal when I was using it as a daily driver. I suppose the gas could be going bad, but I made sure to never fill more than a quarter tank once it was retired, so that I'd put fresh gas in more regularly.

 

[jeep-N-montero]

Actually, the more air space you have in the tank will result in more condensation in the gas, fill it up and add a fuel stabilizer to minimize any effects of letting it sit.

 

[jms_brns]

I didn't know that, thanks for the tip. I'll actually be driving it more regularly now, so I shouldn't need the stabilizer, but I'll definitely fill the tank today.

 

[coffeegoat]

Huh - I have the exact same problem. My thought was actually the Evap system vent solenoid or something else in that system. I've been meaning to get out and look at it, but it's snowy and cold and haven't felt motivated to get to it...

There are a lots of miscellaneous tutorials out there to diagnose/repair it, but I haven't taken the time to look carefully yet.

 

[JohnnyBfromPeoria]

I'll bet you a dollar somebody mixed up the vacuum lines that lay on top of your throttle body. Look where the air intake hose meets the metal part and right beyond that you may see three vacuum lines. Refer to the underhood sticker to make sure they are routed correctly. Let me know where to send your dollar if I'm wrong.

John B.

 

[Toasty]

Ha ha ha! Sounds like experience JBFP. Good tip though.

 

[jms_brns]

Thanks for the tip JBFP, I'll see if I can track that down tonight.

The truck also has an irregular idle, to the point where I was at a light yesterday just after filling the gas tank and felt like I had to hold the brake and rev the gas a bit to keep it from dying while stopped. Then died right as I was rolling into my driveway. Drove it to work again this morning and it seemed fine, though I managed to only stop at one light in the 4 mile drive.

 

[jms_brns]

Well, I kind of ignored this for a while, and then this past weekend the check engine light came on with the code P0450 - fuel tank pressure sensor. Ordering the part now. A faulty regulator with a blocked vent would explain why there was so much pressure in the tank... I'll update once I get it replaced.

Broke 2 bolts removing the cover behind the rear seats, even after the penetrating oil sat on them for hours...:squint:

 

[jms_brns]

So I ended up replacing the fuel tank pressure sensor last week, but the CEL came back on. Called a friend who's a mechanic at Infinity and he looked up some info on it and suggested I see if there was something odd going on with the vent that's just under the gas cap in the fuel filler tube. I took off the gas cap and looked, and the "button" (for lack of a better term) was sticking out about 1/8". I pushed it in flush, then pushed in the fuel filler flap, which popped the "button" back out, but this time it was sticking out about a half inch. I pushed the "button" flush again, then disconnected the battery to reset the CEL. Drove around for 20 minutes, didn't get the light.

The next day, I filled up for some wheeling, and just made sure to push the button back in after filling, and still never got the CEL again. Problem seems to be solved.


Here's the button I'm referring to... I had never even noticed it before this.