4.3 Ltr V-6 Efi Evap Addition

Ever since my 4.3 ltr swap. I've been having fuel tank pressure problems. The original tank pumped the fuel out of the tank. When the fuel was removed. The tank drew air back into the tank through a vent in the top of the tank and the fuel cap. Both only vented in not out.

When I first did my swap I thought I only needed to install a pump in the tank and a return line. I then learned that when I drove it a while. I stopped for gas. When I opened the cap I was confronted with a big gush of fumes from the pressure that had built up in the tank. Seems I needed a vent.

Now comes the problem. How do you put a vent in a gas tank? I thought about it a while. I need to install a vent in the easiest place I could think of. The fuel pick up. It has a vent. I need to remove it and install a roll over vent valve. So I removed the old vent and drilled a hole used a pipe tap and installed the vent valve and I was done. Easy, or so I thought. Now how to vent the line out of the vehicle. Now more thinking. Ah. I could use metal line and rum it up over the rear wheel well and down into the rear wheel well. (Tank under the drivers seat and the line is venting to atmosphere.) This isn't good, but temporary.

Upon driving it a while the vent seemed to work great, until I went off road. The fuel would slosh around in the tank and plug the vent valve. The vent valve has a float that is designed to plug to keep the fuel from going up the line. I had to open the gas cap to relive the pressure. I also notice a lot of fumes coming out my vent line when not plugged. I need a new plan.

I need another vent in the tank and a Carbon Canister. Where do I put the vent and were do I mount a Carbon Canister? The Carbon Canister Needs to be mounted higher then the gas tank. More Thinking.

I need to weld a bung in the fuel tank nozzle and install the vent. I also thought I could mount the Carbon Canister in the rear wheel well. So I did. (WARNING WELDING ON A GAS TANK IS DANGEOUS. Please leave this up to some one who knows how to do it. )
Here's my pictures.


Fuel pick up Roll Over Vent Valve.


Fuel pump and return line.


Nozzle Vent.


Complete fuel tank plumbing.

Carbon Canister


Carbon Canister mounted in the wheel well.


Emissions Routing label. 1995 S-10 Truck. (Manual Transmission Only)

 

Is there a hose running forward to manifold vacuum to pull the vapors from the canister? Is the purge valve hooked up electrically? Can the canister be oriented like that vs vertical? I know it's a lot of questions but someone's going to ask. This is going to be a big help for those installing a modern fuel injected engine. Nicely done.

 

In the manual transmission 1995 S-10. There was no Purge Valve. I found it strange. The same motor with the auto had it. Weird. (Info. Factory Service Manual.)
My vacuum line runs straight to the Carbon Canister. The Carbon Canister I used came from a S-10 pickup. It was originally mounted just like I have it. And I really don't see why one couldn't mount it in any orientation.

 

Every conversion I've seen done to either TBI or EFI the vacuum canister was omitted. How required is it? Should I factor one into my project?

 

Do you really want fuel vapors venting to atmosphere? When my tank was pressurized. I was amazed how much fuel vapors were venting from the tank. I had to open the gas cap to relieve the rest of pressure. Not Good.

 

You've just described every vehicle made prior to 1971. I'm aware there is an emissions component to the use of EVAP canisters, I was just wondering if you had any performance issues with your engine which prompted the change or if you were just worried about the pressure and fumes?

 

No performance issues, just trying to properly venting my tank.