Question about ventiltaion box in rear fender (Brat)

[SaltyMike]

Hey everyone,

Recently I've been having issues of what appears to be an excess amount of pressure building up within the fuel tank. I know that there is always supposed to be some pressure that releases whenever you remove the gas cap, however this seems to be an excess amount to me. It's to a point where it may take two hands to take off the fuel cap and will result in major fuel spray if not removed super slowly. Coincientally, I just started noticing this after having done my EJ22 swap, but nonetheless I suspected there was a blockage in one of the fuel/vent lines. None of the lines are crossed, and I was able to hearing bubbling in the fuel tank when blowing air into the return line, so it must not be the return line that's blocked.

Through doing some fuel system research, I learned that there is a ventilation box for the fuel system that is located in the passenger side fender, so I checked that out to see if anything was gummed up in it. I found that the box has three lines connecting to it. Two of the three lines are have roughly the same small diameter. However, the other line is a lot larger in diameter (at least at the point where it connects to the vent box, it seems to taper down to a small diameter similar to the other two as the line continues). I blew compressed air into all three connecting points on the vent box itself and nothing indicated that there was a blockage on the inside (I'm unable to take apart the box itself to inspect it.) Next step was to blow air into the three lines that connect to the box. When traced, one of the two small diameter lines connects to the passenger side of the fuel tank. The larger line also connects to the passenger side of the fuel tank. The other small line is the vent line that pops out through the fire wall, and by blowing compressed air into it I confirmed that it was not blocked. The small line that connects to the fuel tank blows air out of the fuel fill port itself when the compressed air is introduced. However, nothing is heard when blowing compressed air into the largest line. 

Would anybody have an idea on what the largest line connectiing to the ventilation box does? Is what I am describing indicative of a blockage somewhere? 

[el_freddo]

I find in summer here that my fuel tank can pressurise quite a lot on a hot day. I don’t open my fuel tank unless I’m on empty so there’s no fuel to be sprayed at the filler cap for me. 

I don’t have an EJ under the bonnet (yet!). 

The other thing to check out is to see if the purge control solenoid is operating properly on the EJ - it’s under the intake manifold on the RHS from memory. If this isn’t working properly it should throw a CEL I believe. 

If this pressurisation occurs in the cooler months I’d investigate to work out what’s going on, otherwise I’d just put it down to it being warmer and the EJ circulating the fuel more which to me would result in more pressure in the tank. 

Cheers 

Bennie

[SaltyMike]

On 10/23/2023 at 5:38 AM, el_freddo said:

I find in summer here that my fuel tank can pressurise quite a lot on a hot day. I don’t open my fuel tank unless I’m on empty so there’s no fuel to be sprayed at the filler cap for me. 

I don’t have an EJ under the bonnet (yet!). 

The other thing to check out is to see if the purge control solenoid is operating properly on the EJ - it’s under the intake manifold on the RHS from memory. If this isn’t working properly it should throw a CEL I believe. 

If this pressurisation occurs in the cooler months I’d investigate to work out what’s going on, otherwise I’d just put it down to it being warmer and the EJ circulating the fuel more which to me would result in more pressure in the tank. 

Cheers 

Bennie

I appreciate it Bennie, it’s cooled down a bit over here in New England and I’ve noticed it happening less. I will keep an eye on it though and check the solenoid.  Thank you! 

[Steptoe's photos]

that third line may be connected to a higher point of th tank , so may not give any hint that air is feeding in as you add air pressure - no bubbling noise etc - actually both are probably high up. I have a tank out at the moment I could look at... and come back later