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Discussion Starter · #1 ·
Making plans for a custom tank and I'm a bit confused by the number of hose connections on the stock tank.

My understanding of the fuel system is as follows:


But, this only accounts for two hose connections on the tank (excluding filler line and pump output)

In fact, there are four connections (three on the left, and one on the right). Where do the extra two lines go? And is my diagram otherwise correct?

 

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You have a vent for the filler, one for the tank, a couple roll/vent valves. When you build a tank, you want a 5/8" vent, filler neck, and a couple rollover valves. Easiest is to just use YJ valves. Just make sure that either the evap or the lines tot he evap are above the tank, or fuel will run into the evap and stall the engine.

You only need two small vents. Use a T and make it into one line into the evap.
 

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The stock fuel tank fittings are complicated to understand. The JK uses a single line fuel feed with the regulator and filter built into the tank.

The tank is vented to the EVAP canister through the large fitting.

The EVAP canister is vented and purged by a purge valve and EVAP system integrity monitor(ESIM).

The line from the EVAP canister to the intake as you illustrate it is the purge line and will go through an ECM controlled purge valve.

The smaller vents on the tank are just that vents.

The one you must be careful with is the fuel filler neck vent, it is not just vented into the tank, it controls a fill valve that allows fuel to be pumped into the tank based on differential pressure. If that line/valve is not working properly you may have a hard time getting fuel to go in.

If running a stock tank it is important the lines be hooked up properly, if you are fabricating a tank it doesn't really matter.
 

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Discussion Starter · #7 ·
You have a vent for the filler, one for the tank, a couple roll/vent valves. When you build a tank, you want a 5/8" vent, filler neck, and a couple rollover valves. Easiest is to just use YJ valves. Just make sure that either the evap or the lines tot he evap are above the tank, or fuel will run into the evap and stall the engine.

You only need two small vents. Use a T and make it into one line into the evap.
I have a confusion on the evap line not being flooded with fuel when off-camber with a full tank even if the line is run from the top of the tank. Consider this example of the stock setup. Isn't this a problem?

 

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I have a confusion on the evap line not being flooded with fuel when off-camber with a full tank even if the line is run from the top of the tank. Consider this example of the stock setup. Isn't this a problem?

Yep. I had to reroute lines up into the back corner. Sort of like routing a vent line, it is up above the brake light. Prior to that, I tried not to fill the tank past half full or wheeling was not fun. Rerouting the lines was a PITA too.
 

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Discussion Starter · #9 ·
Yep. I had to reroute lines up into the back corner. Sort of like routing a vent line, it is up above the brake light. Prior to that, I tried not to fill the tank past half full or wheeling was not fun. Rerouting the lines was a PITA too.
Would using rollover valves at the vent lines on the tank to the evap solve the issue I drew without needing to worry about any special high hose routing?
 

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The stock fuel tank fittings are complicated to understand. The JK uses a single line fuel feed with the regulator and filter built into the tank.

The tank is vented to the EVAP canister through the large fitting.

The EVAP canister is vented and purged by a purge valve and EVAP system integrity monitor(ESIM).

The line from the EVAP canister to the intake as you illustrate it is the purge line and will go through an ECM controlled purge valve.

The smaller vents on the tank are just that vents.

The one you must be careful with is the fuel filler neck vent, it is not just vented into the tank, it controls a fill valve that allows fuel to be pumped into the tank based on differential pressure. If that line/valve is not working properly you may have a hard time getting fuel to go in.

If running a stock tank it is important the lines be hooked up properly, if you are fabricating a tank it doesn't really matter.
There's something here I'm not understanding.

It's this part. "The smaller vents on the tank are just that vents."

Why go to all the trouble of installing all the EVAP stuff if you still have just plane ol vents on the tank? Are they check valved to only let atmosphere in? As a way to keep the tank from creating negative pressure inside?
 

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There's something here I'm not understanding.

It's this part. "The smaller vents on the tank are just that vents."

Why go to all the trouble of installing all the EVAP stuff if you still have just plane ol vents on the tank? Are they check valved to only let atmosphere in? As a way to keep the tank from creating negative pressure inside?
No Kevin they do not go to the atmosphere. The top of the JK fuel tank has high and low points so multiple vents are run to efficiently vent the tank. If you had a dual hump fuel tank like the Genright or a BMW tank and you vented only one hump there would be a problem.

The JK runs one EVAP vent up front and a second in the rear tower, both these vents pass through the ring in the rollover/fill valve and into the EVAP canister where the vapors are purged out by the purge valve or vented into the atmosphere under certain conditions. The early JK did not run a fuel tank pressure sensor so the PCM does not know FTP and depends on the spring loaded ESIM to vent if purge is not enough. The ESIM does contain a switch for EVAP monitoring to detect small and large leaks.

The fuel filler vent line is a different animal it controls a fill valve that allows fuel to be pumped in based on differential pressure.
 

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No Kevin they do not go to the atmosphere. The top of the JK fuel tank has high and low points so multiple vents are run to efficiently vent the tank. If you had a dual hump fuel tank like the Genright or a BMW tank and you vented only one hump there would be a problem.

The JK runs one EVAP vent up front and a second in the rear tower, both these vents pass through the ring in the rollover/fill valve and into the EVAP canister where the vapors are purged out by the purge valve or vented into the atmosphere under certain conditions. The early JK did not run a fuel tank pressure sensor so the PCM does not know FTP and depends on the spring loaded ESIM to vent if purge is not enough. The ESIM does contain a switch for EVAP monitoring to detect small and large leaks.

The fuel filler vent line is a different animal it controls a fill valve that allows fuel to be pumped in based on differential pressure.
Ahhhh, ok, that makes perfect sense. Thanks for the explanation.
 

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The stock fuel tank fittings are complicated to understand. The JK uses a single line fuel feed with the regulator and filter built into the tank.

The tank is vented to the EVAP canister through the large fitting.

The EVAP canister is vented and purged by a purge valve and EVAP system integrity monitor(ESIM).

The line from the EVAP canister to the intake as you illustrate it is the purge line and will go through an ECM controlled purge valve.

The smaller vents on the tank are just that vents.

The one you must be careful with is the fuel filler neck vent, it is not just vented into the tank, it controls a fill valve that allows fuel to be pumped into the tank based on differential pressure. If that line/valve is not working properly you may have a hard time getting fuel to go in.
Hey Motech / Robbie, I bolded the main issue. I am having exactly this problem. My fuel tank does not seem to be venting correctly and having an awful time filling the tank. Is there a fix for this? Or is the vent inside the tank and not repairable? I was told by Jeep that I have to replace the entire tank. I am hoping this is not true.
 
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