LS Swap Fuel System Help

[GSD Guy]

Hi, I bought a Blazer a while back that has been mostly sitting in my garage because of a fuel leak and lack of time. I finally started to track it down and would like some advice on what to do. It was swapped with a 5.3L prior to me owning it but the fuel system routing doesn't seem that great. It has what looks like a stock style tank with an inline fuel pump that pulls from a stock sending unit (which doesn't seem to be reading correctly either).

The return line is soft hose until in front of the rear axle where it then connects to the evap system vent line that would normally go to the charcoal canister (the charcoal canister is no longer in place). From there, at the back driver's side of the tank, the end of that hard line is connected to the passenger's side vent hard line which is connected to the passenger's side vent on the tank so this is where the fuel is returning to the tank. Seems like a roundabout way to return fuel to me, but again, not my work.

The driver's side vent is connected at the tank to the hard line which is then open at the rear, so obviously when gas is sloshing around it's coming out of this line. None of the three lines are connected to the container in the bed but I can't just connect this line because the evap system is no longer intact. My question is, can I just cap the driver's side vent at the tank and get a new vented gas cap? And following up to that, is there an easy plug to cap that with and are the stock 72 gas caps vented? Or will I need one from another year prior to the evap systems?

Thank you everyone!!!!

[GSD Guy]

Monday morning bump, any help is greatly appreciated!!

[hemi43]

No answers because your post is too difficult to understand. Pics would help.

[GSD Guy]

Picture may be difficult being that everything is in place. Basically:

1. Charcoal canister is gone and evap system isn't intact.
2. Fuel is being returned to the tank via the vent on passenger's side.
3. Driver's vent is open and leaking fuel.

Can driver's vent connection be plugged and a vented gas cap be used without causing more problems? What's the best/easiest way to plug the vent connector?

Thanks!

[jaros44sr]

no. 3, how about a rollover vent, like a motorcycle style

[underliner6]

I swapped an LS1 into my 72 Camaro. I don’t know if you are using the stock regulator in the 5.3 fuel rail but this is how i did it with my LS1. Stock tank > stock sending unit > EFI hose> inline fuel pump > EFI hose > C5 vette regulator that sends one hose as a return line to the sending init and one hose all the way up to the fuel rail. I did not use any of the stock hard-lines. It’s was easy and has worked well so far. If you don’t want to problem solve the PO’s fuel system you could always replumb it like this. Hope it helps.

PS- all you need is a little micron in-line fuel filter between the regulator and fuel rail to filter.

[mcmlxix]

Depending on the year of the of the LSx swap motor, your fuel rails may or may not have a return line and it may or may not have a built in regulator.
If you need a return line, look at one of the vendors and buy a second hard line that runs back to the tank.

External fuel pumps do not do well if they have to pull fuel from in the tank when the pump is mounted above. They do better to feed from the bottom and only have to push the fuel up to the motor. In-tank pump is always the better option.

My 6.0L swap has no return and no regulator. I used a fuel pump module from the same year truck my motor came from, 2005. I got a mounting ring from www.vaporworx.com ,however I made a custom tank, it could still be retrofit into a stock tank.

[A1971Blazer]

Here's a couple of pics of a '71 that I had for parts...hope this helps


Driver's side...you're saying that the front vent is open and leaking?
You definitely need to plug it

Also...as mentioned the pump may not last long if it's having to pull....fuel pumps are designed mainly to push

The fill vent...with the hose clamp...needs to be open for filling..it runs to the top of the filler neck...and yes use a vented cap


The passenger side vent is part of the evap system...you're using it for the return?

[GSD Guy]

Thanks guys! Unfortunately I'm not in a financial spot right now to redo the fuel system with an in-tank pump. I know the inline isn't ideal but it doesn't need to be daily driver reliable as it hardly gets driven.

A1971Blazer,
Yes, the driver's side front vent is open. Is there a vacuum plug type plug that I could put over the barb fitting? I haven't been able to find anything online like that.

Fill vent is intact and open to the fill neck. Would a stock 72 gas cap be vented? Or no because of the evap system?

Yes, passenger's side vent is being used as the fuel return. For what it's worth, it's a 2004 5.3L so I'm guessing based on what is there that the return is necessary.

Thanks!

[mongocanfly]

does it have a inline vett style filter/reg or are you using the factory bypass from the fuel rails?
as long as the unused fuel is getting back to the tank it shouldnt matter what route it takes
there is nothing wrong with a inline pump system as long as its setup proper...been running one for yrs with no issues
if you are just wanting to plug that vent line then just stick a bolt in the hose and put a clamp on it....may not be the best fix for now but way better than a fire

just to clarify
(1)so this is where your pullin fuel from ?
(2)and this is where it bypasses back to the tank ?

[GSD Guy]

Mongocanfly,

Correct, fuel is drawn from 1 and returned to 2. I’m assuming the stock bypass is being used. Both lines run to/from the fuel rail with nothing inline but the pump.

[Haggar]

On mine, I run an aeromotive phantom fuel hat/module with a Walbro 255.

Plumbed like:

Fuel out -> Corvette Regulator - > Fuel Rail
Corvette Regulator Return - > Return fitting in fuel hat (inside the tank, this is piped down to squirt back into the module, low down to minimize aeration)
Fuel Hat Vent -> Looped line with a filter/rollover valve, located high up behind my left tail light

All of my 'stock' vents are capped. Note, this is an aftermarket Poly tank, but it is for the Jimmy.

As far as I know, the fuel cap is stock.

No issues with this setup in the last 3 years.