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I never had an operational 4.2 but generally an evap charcoal canister does the following.

The vent line to the canister from the tank should have zero suction resistance. Then there’s two lines to purge the canister- one is a limiting vacuum valve from the manifold that “opens” the purge line to the engine, and the other goes to either a choked manifold port or the air cleaner. Some applications have four connections and I can’t recall if the jeep 4.2 has 3 or four.
 

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Discussion Starter · #82 ·
I never had an operational 4.2 but generally an evap charcoal canister does the following.

The vent line to the canister from the tank should have zero suction resistance. Then there's two lines to purge the canister- one is a limiting vacuum valve from the manifold that "opens" the purge line to the engine, and the other goes to either a choked manifold port or the air cleaner. Some applications have four connections and I can't recall if the jeep 4.2 has 3 or four.
the 4.2L has 4 total, one is the purge signal, one from the gas tank, one from the carb float bowl, and one from the airbox/pcv

Is the purge signal supposed to allow suction or is it just a vacuum switch, because there's no air flow on the line

Also, the bottom of the charcoal canister is open to atmosphere so there's no actual suction from the manifold to the gas tank
 

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Discussion Starter · #83 ·
Okay so I dropped the tank and pulled the sending unit since it has been needing to be replaced.

A few things I noticed:
The strainer in the tank has disintegrated and left pieces of plastic and filter floating around. When running the pump to drain the tank it was pumping very slow, which means there must have been an upstream restriction.

I'm thinking those filter pieces clogged the pump or the inlet line, causing the restriction on the inlet. I drained it dry and removed everything so the tank is nice and clean now. However, I'm still installing the in-tank pump because it wasn't much more work to do that, and it has a new strainer.

This should hopefully fix the issue once and for all.
 

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Discussion Starter · #85 ·
Another thing I noticed when putting the tank back on is that it’s VERY easy to pin the fuel lines between the tub and the tank if you don’t yank on them to pull them into the slightly higher groove that’s further forward, it doesn’t help that the metal pipes coming out of the tank are pointing toward that section

This may have also been the issue since it would have pinched the inlet line and cause a big restriction

I installed the in tank pump, unfortunately it doesn’t exactly drop in as is (unless the pump I bought had some manufacturing issues)

I cut off the bottom of the return line because it was about a half inch too tall and would hit the bottom of the tank

The pump strainer also hits the bottom of the tank but if you unbolt the bracket and turn it 180 degrees it drops into that recessed section of the polymer tank and fits perfectly. But to do that you also have to cut off most of the output pipe so that the pump outlet can connect to it without an extreme S bend. The strainer also touches the wall of the tank so you’ll need to bend the plastic insert thing upwards on the end so that it can sit better. I also put a hose clamp around the fuel pump to help secure it better (with some rubber around it so it won’t vibrate and make noise)

it’s now running with the in tank pump and seems to be doing good. Also the body harness on the YJ has wiring for the in tank fuel pump already so you can pull the firewall connector in the engine bay and add another pin in the fuel pump slot to run power directly to the sending unit connector without having to run wires back to the tank
 

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Discussion Starter · #87 ·
Another update, I lost all fuel pressure on the highway again and needed to be towed home

I think the pump outlet line popped off inside the tank, but now I need to disassemble it to find out
 

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Discussion Starter · #88 ·
Another update, I lost all fuel pressure on the highway again and needed to be towed home

I think the pump outlet line popped off inside the tank, but now I need to disassemble it to find out
Further update, got towed home and dropped the tank again, yes I popped off the fuel line inside the tank, whoops

Either it wasn't tight enough or I need to figure out how to get it to not come off since I cut off that bump section when I modified it
 

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Discussion Starter · #90 ·
Not sure those fittings will stay put without the flare on the end....
You can rent the flare tool at AutoZone if you have one nearby.

Sent from my SM-G960U using Tapatalk
Yeah I wasn't sure, but the fuel pump output also doesn't have a flare on it and that one stayed on

I scuffed up the pipe so it wasn't so smooth and made sure the lines were tight this time, I'll see if it pops off again but at least I know the quick way to drop the tank now

Also I found out the tank has a groove built in for the fuel lines that I haven't been using, so I tucked them in there
 

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Discussion Starter · #91 · (Edited)
Realized I never gave a final update on this thread

It has now been a year since the in tank pump install with the "fixed" scuffed fuel line so it doesn't pop off. I have not had a single fuel issue since that point. This included towing a trailer 1000 miles through the dead of summer heat in mountainous areas, so it's safe to say the sputtering and dying issue has finally come to a close.

The new issue is with my larger tires the engine is now overheating on long uphills LOL so I just installed an oversized radiator (it did have the oem radiator from when I bought it so it could have been 12 years of corrosion and buildup causing that. Did a full coolant flush and replace so that should be it. Let's goooo

I think the original problem traced back to the first time I dropped the gas tank in 2016 to replace the fuel lines. The gas tank has a built in groove for the lines but I didn't notice that so I tucked the lines in on top of the tank, and when bolting the tank back on I think I compressed the fuel lines against the body which put a heavy restriction on my inline fuel pump, thus causing the pump to vapor lock in hot weather. I made sure to put the lines into the groove this time when I installed the in tank pump.

Now I have a second car getting a fuel injection swap...not making this mistake again!!! making sure none of the fuel lines are pinched
 
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