What is causing my gas cap to make this.. odd squeal? trill? I don't know what word to use sound

So this sound has been happening for nearly 2 years now with my 2022 sport MT since about 30,000km (now at 90,000km) periodically while in motion, usually while off roading or on warmer days. It is really only audible when next to something to reflect the audio. I managed to record it while driving out the window and then asked multiple mechanics/dealers over the years what it was, but no one could identify it or seemed to have heard it before. I was also always at a loss for how to describe it so I'm not too surprised

as it only happened while in motion I was never able to pinpoint down where it was coming from let alone what was causing it, until now! (I think)

was offloading up by stewart BC at the salmon glacier nothing hard or special just bumpy dusty steep roads and after a small creek crossing of 10cm of water the trucks starts to idle rough, throws codes P2196 P2198 and the sound starts to become constant. like every 5-10s constant and even when not in motion anymore. get out of the truck and track it down to of all things my gas cap .

so the sound:



When I took the gas cap off there is an obvious draft of air into the tank and the truck starts idling much rougher (I was going to take a video too but it idles so rough it sounded like it was going to stall)

Decided to GTFO and got the 60k back to Stewart gas station (and when I was at the border the officer did comment on this sound my tank was making, worried because he also had a tacoma lol), turned it off and it dieseled/ran for a couple seconds after, took many cranks to start back up. drove 300km or so to Smithers (nearest place with stores) and I did get a check engine light for about 10 min a 3rd of the way, new codes (P0172, P0175) but it got me there however when stopped it idled fine. no sound. turned off fine and started fine, cleared codes and they didn't come back.

got me some MAF sensor clean and cleaned the MAF. once right after during idle it dipped once and threw codes but then after 20-30m more idling none. drove some back roads for an hour pushing the truck real hard up some steep stuff drove fine no codes BUT the sound was back at its original once in a while only while driving. revved sitting to 4/5k and it threw the codes again. cleared and revved it multiple times after to 4/5 k no codes.

so while I seem to have fixed (for now) the issue that allowed me to track down the sound, the sound still persists. the sound when not running rich? is ofter much longer/drawn out too

anyone have any idea what could be causing this?

tl;dr: odd sound from gas cap, see https://www.dailymotion.com/video/k3cRqgryf6d3lbBgiSq, worse when running rich?, what cause?

 

I would check the Evap system and make sure nothing is clogged.

 

The sound reminds me of the sound that my old VW Beetle (original style) with a pinched vent line made. On a drive from OK to Calif it actually collapsed the fuel tank.

 

Gonna spitball this to the vent system, here are the parts and diagram. Likely a damaged or clogged vent component.
https://parts.frontiertoyota.com/search?search_str=Fuel+Tank+Vent+Hose+2022+tacoma

You will see diagrams like this when you click on the parts.



@b_r_o feel free to opine

 

Evap

 

Somebody keep filling gasoline after the first click, at the pump? What others said, most likely EVAP.

 

I always do 1 click pause 1 click

Had it looked at and verdict seems to be the purge valve was stuck open. Bypassed while waiting for a replacement part and so far seems to be running fine again

 

What is “1 click pause 1 click”? It sounds like you are overfilling it. These new automobiles do not like being overfilled, so I’ve been told. Gas goes into the evap system and causes headaches. Personally I’m too lazy to overrule the gas pump.

 

Could be. Let it fill up by itself. Once it stops, don't put anymore fuel in or you'll fubar the evap system.

 

fill till it stops. pause a sec. fill till it stops stops again as some pumps will click off really early. a far cry from topping off the tank with as much as I can.

rest of the evap system looked fine and iirc its not the purge valve that is damaged from topping off its the evap charcoal canister

 

Has the cap been replaced yet? Usually it's the cap that causes that...

 

causes the purge valve to misbehave/fail?

not yet but its cheap so worth a try to prevent it from happening again.