Fuel Return & Vent Lines

[Neuner]

Have steel fuel return and vent lines extending to the front. PO plugged one of the lines. They had a single input/out fuel filter and I installed a Holley pressure regulator so never needed it until now. The other was connected to a canister which I hope is the vent.

I'm needing to use the return line now and I'm not confident he had it correct since I've also found other PO mistakes.

I've traced the two back and they disappear back to the tank in the same location. I really don't want to have to drop the tank to get my answer. I need to save that for some other time to keep the family happy.

The line that was plugged appears to be thinner, 5/16(?) than the vent line, 3/8"(?). Looks original and un-molested. Is this correct?

 

[Hedgehog]

The vent line should be the smaller of the two. Hmm wait, that would be the return fuel line should be smaller than the fuel line.

 

[Neuner]

Well, I was thinking the same thing until I noticed that one of the two is the same size as the fuel line. The larger sized one (same as fuel line) is what the PO had connected to the canister as the vent and the smaller one was run up near the engine and capped off. It was the size difference that is making me wonder if the PO had them wrong.

 

[Torxhead]

An improvement would be to convert the oem 1/4" return line to 5/16". You should be able to find a diagram in a repair manual and see how the check and rollover valves go with it. It goes to the fuel tank next to the fuel outlet line. http://i973.photobucket.com/albums/ae214/k6ruv/79 Jeep/79FuelandVaper.jpg

 

[Neuner]

That helps! So the small one is the return and the PO had it correct .


Ya, you're right. It would be an improvement and I need to do that.


I've never dropped the tank before and really don't have time for it. Would I be able to just drop the front or back side of the skid plate enough to finesse a new line up in there? My wife is going to kill me...

 

[hagar]

An improvement would be to convert the oem 1/4" return line to 5/16".

I wouldn't advise doing that.
It's 1/4" diameter for a reason: fuel return to the tank.
You want that return line diameter smaller than the fuel line that's feeding the engine.

 

[Torxhead]

Neuner, I would suggest dropping the tank, since it has probably collected quite a bit of in it over the years plus the pick up sock might be in need of replacement by now. Remove the gas first, an auto parts store should have a manual siphon/pump that you can purchase to help you with that. I have also seen where the big box 4wd outfits sell a stainless pickup sock that should last awhile. It is a lot of work of course.

 

[Neuner]

Oh I know but am just needing to avoid it for now. When I do it, I'm hoping to get everything corrected with the tank, sender and an access panel like everyone else does but I really just don't have the time that it would take. I just spent a lot of time doing a 4.0 swap and the family has had enough of me spending my free time in the garage. I can't blame them, I'm at my end as well. Ready to just run the damn thing off of a cliff if the 4.0 wasn't so awesome.

On top of that, I fumbled the 300 during install and think I either busted a seal or the casing. It never leaked before and now it leaves puddles after even a short drive. Another time consuming ordeal that I'm trying to avoid for the time being.

I finally got the pressure down to spec at the fuel rail with a WJ fuel filter/regulator and the engine runs great until I have to idle at a long light. The thin return line has got to be too restrictive with a 1/4" size, causing build up of pressure at the rail over time and creating the problems I'm having. I've been revving it while stopped to burn off the excess pressure. I already blew one injector, I'm not ready to replace another.

I've been researching a new, larger, temporary return line that would branch-off or "T" before it goes back to the tank. I'd have a branch that would loop back to the pump inlet. Appears some of the diesel guys are doing it to moderate their pressure. Just need to get rid of any air bubbles that may develop with such a loop. Haven't found too many who have done it and whether or not it will work. Something like the attached pic but it would also branch back to the tank return. Oh well.

 

[Neuner]

Rough drew up what I'm thinking about doing for a temporary solution. Based off of similar systems for diesel and veg oil.

I'll have to keep air out of the system where the return line splits. Thinking about another fuel filter/regulator. Maybe the old one for the AMC 258 i6 / 4.2l will work?

 

[Neuner]

Well, never mind. Got a different pressure tester that doesn't leak and the pressure stayed constant whether revving or idling so the return line isn't the issue. Only acts up when idling and in closed loop so going to replace the IAC.