I don't have 100% confirmation but I am pretty certain the port I have circled in the above pic is the main tank vapor vent to the charcoal canister, and that is how I have mine plumbed. I also altered my fuel vapor purge valve plumbing to be just like the pic below - I now have the purge valve 'opening' port (the port that signals the main valve to open and let the vapors through) going to ported vacuum (requires 10% or more throttle opening to generate vacuum/not a constant vacuum), and have the through-port going to full vacuum at the throttle body, which I think will work much better...at least for my 'old school' application.

Also, I just got a junkyard gas tank with the big 'whatever' valve, and I'm going to mock it up in a bucket and test each port for its function, and I'll report back. Meanwhile, here's how I'm doing my vent system -



- Sam

 

Any idea what happens if you eliminate/cap off the red line?

 

...honestly I don't think much of anything would happen - I just did some testing and I think that line simply allows vapor to flow from front to back of any given tank to help equalize pressure...I think. See below -

--------------------------------------

ok - I've been wanting to confirm what the individual ports actually 'do' on the big "rollover" or "main" or "whatever-it's-actually-called" valve on top of the JK gas tank, and to that end I went to the local u-pull-n-pay and nabbed a Ram tank with the same valve on it (apparently sharing the same main valve on many Mopars over the years).

To keep things clear as old fuel, here's a pic showing the terms I'm using -

Main valve -


underside -


Rollover/transfer valve -


underside -


First thing I wanted to confirm is whether or not the smaller rollover/transfer valve would leak fuel when submerged and upside down, so before I extracted the valves, I turned the tank upside down and filled the back end with water (thus 'submerging' the rollover valve in liquid/simulating a rollover or steep incline), and indeed confirmed that the rollover valve will not leak liquid when completely submerged and upside down - I think all it does is allow fuel/vapor to 'transfer' from front of the tank to the back, and vice versa.

Next, I cut out the two valves from the tank - the main valve and the rollover valve - trimmed the edges of the main valve, bolted it to a Homer bucket lid, filled the bucket with water, attached the lid, and turned the whole thing upside down to see what leaked out of where. Nothing seemed to leak from the rollover port, but the big vent and small vent initially leaked some water...but then stopped leaking - I guess there is some sort of valve in there to prevent excessive drainage when submerged and upside down - in my case when the front of the Jeep is up on a big obstacle and all the fuel is fully pressing against the valve - I wanted to know if fuel would just 'gush' out the big vent (which I am using solely as my filler neck vent)...and now I know that a little will leak out - maybe half a pint?, then stop, and that's good news.




Next, vapor venting. Using some compressed air, I hit each of the three ports to see what air escaped from the other two ports. Hitting the rollover port, a lot escapes out the main vent and a tiny bit out the small vent. Ok not bad - again this is a vapor test. Air in the small vent causes a tiny amount out both the main vent and rollover vent. Couldn't get a good seal on the main vent, but it didn't seem to result in much out either the small vent or rollover vent.

Then, the 'filler-up' test. With the lid on the bucket, I drilled a small hole in the lid, then hit it with air - the main vent indeed vented a lot, which is why when I fill up the Jeep it fills up fast and shuts off the pump perfectly. I have the main vent going directly to the filler neck exiting about 3 inches below the cap, and it seems to work perfectly.


Here's how I have the big main vent going direct to the filler neck -


I have the small vent (the overall tank vent to the charcoal canister) going directly to a charcoal canister, however I only had about a foot of hose between the vent tube and the canister. Knowing the small vent leaks a bit of liquid when submerged (or in my case with the front end up on a steep obstacle), I think there may be a decent chance of some fuel making its way through the tube into the canister, which I don't want. So, I'm going to add a couple more feet of tubing to the equation as well as a 1/4" clear fuel filter (Wix 33001), so I can actually see whether or not any fuel is leaking past the valve towards the canister, and if so it'll just puddle in the filter before making it into the hose.

Doing all of this along with the [fuel vapor purge valve] plumbing adjustments described above and I think I'll have a pretty decent way of venting fuel vapors to the throttle body. I may also add another length of hose to have the fresh air draw come from the air cleaner hat, which should fully seal the system.

So...I know this all doesn't exactly 100% verify how the big mongo main valve actually functions on these tanks, but for me it does eliminate some of the ambiguity. And again, I'm just trying to keep the immediate area around our Jeep smelling more like a newer vehicle and less like an old musclecar - as 'clean' as prudently possible, and while these tests aren't exactly 'laboratory' precise and a Homer bucket certainly isn't exactly laboratory certified equipment...for me it suffices well enough in trying to find a suitable way to keep things good enough for my simple machine. I'm diggin' it 👍

- Sam

 

UPDATE: Had the Jeep out on a trail run the other day and NO fuel smell coming from the charcoal canister - that may just be luck but I'm inclined to believe the new fuel vapor purge plumbing is now working as it should .

Meanwhile, took the whole family...for the first time ever...out in the Jeep to our local Ram Off Road Park for a bit of fun...and wouldn't ya know just as we're all done and making our way out...the engine just...shut off...leaving us temporarily stranded...well I should say the fuel pump did. It was a new fuel pump module assembly...and yah it was an "Amazon" or local parts store purchase (don't remember which), and as such apparently the module did not come with a quality pump - no brand name nomenclature on it. Fortunately the park owner is a friend of mine and he was able to strap us back to the trailer, and home we went.

Next day I started to diagnose the problem - the fuse was intact and sure enough there was power getting to the plug, but the pump no workie. SO - since a fuel pump was required I took the opportunity to use only my trail tools and simulate a fuel pump swap 'on the trail'. I had all of the tools to both get the pump assembly out and get the pump itself out, but I'm adding a couple specialty tools to make the process that much smoother...and thinking about it I'm just gonna put together an entire duplicate pump assembly to have on hand to make similar future shenanigans that much easier. And wow I can't say awesome it is having the trap door above the pump and NOT having to drop the tank to change out the pump - it works positively perfectly 👍 -

First...break all of this out -


...unbolt the rear p-side seat base and bungee it up out of the way -


...disconnect the fuel line and electrical plug and strap them up out of the way, grab the retainer ring wrench, crack the retainer ring loose, and 'pop!' - up springs the top end...

Note, and word to the wise - make sure the tank is only about 3/4 full in order to avoid having about 5 gallons of gasoline flood out all over everything under there...which thankfully did not happen only because I hadn't yet refilled the tank - there was literally about 1/8" of air between the top of the pump module and the fuel level, so that worked out just fine, but wow would I have been pissed if it had been full.

So, once I got over the realization of just how lucky I was and my heart rate returned to normal, I grabbed a trash bag to cover the Jeep's floor from drips of gasoline, slowly lifted the module partially out letting fuel drain off of it as much as possible as I lifted, disconnected the forward-aiming extension rod and suction tube, and with the tube in hand lifted the module all the way out, then lay the suction tube on the rim of the tank opening, and brought the module to the work bench for surgery.

Note - anyone with a JK can indeed cut out the required section of floor to get 'access' to the pump module without having to drop the tank...but you must be very careful not to cut too far downward and I HIGHLY recommend covering the top of the entire tank with a fire blanket to prevent hot shrapnel from getting to places they shouldn't be - fire = bad m'kay -


Note - because of the long tank, a JK's fuel pump assembly is designed with an internal surge tank, retaining fuel within an internal cavity that is always full even if the fuel level get's low, and this cavity will still be full of fuel so be careful not to tilt the module too much otherwise you'll get a bath you don't want.

Grab a drain pan, and then tilt the module to drain the fuel. Once drained I disassembled the "non-serviceable" totally serviceable assembly, and removed the junk fuel pump. A quality Delphi pump (my intel says is pn# FE0700 - not the whole module assembly - just the pump) is on the way from Rock Auto (~$100 shipped), and it is indeed a direct match. Here's the "non-serviceable" pump module disassembled for "service" -




Not sure if this is very helpful to anyone, but it sure has been helpful to me...

 

yep it was the pump; new pump is in and functioning as it should

 

Again, not sure if these'll really help anyone...but they sure help me. These are a series of video's I did (very low budget) which may help anyone who has questions about the JK fuel pump module, and how it all works, pumps, fuel pressure regulators, how it all gets assembled/installed, etc.

Intro - https://imgur.com/ll9UNWv
Cleaning debris - https://imgur.com/x4Pgl21
Delphi Pump FE0700 - https://imgur.com/QTVTAXS
Pump in & Pressure Regulator - https://imgur.com/zuV7zrz
Strainer, clips - https://imgur.com/AlR39Cj
Assembly - https://imgur.com/PW43rAq
Pump Wiring Connector - https://imgur.com/TQGLQWl
-- (edit: Fuel level assembly is from ISSPRO; fuel return line is from EFI Sys Pro)
Trap Door - https://imgur.com/3Nb7D9u
-- (edit: I misspoke on the wiring schematic - correct in next vid)
Wiring Schematic - https://imgur.com/dnJcMty
Pickup Tube - https://imgur.com/xC7ooYc
Installing Pump Module - https://imgur.com/pSbH317
Retainer Plate - https://imgur.com/P2sE34Z

- Sam