Fuel system question:

[Ryans71]

Background:
So this weekend I went wheeling. Towed the Bronco from my house (~500' elevation) straight the trailhead and up the trail. The trail climbs about 2,300 feet and takes about an hour. It's about 85 degrees out. 1/2 tank of fuel in a 23 gallon EFI tank. Bronco has '89 Mustang EFI and was running at a normal operating temp (NOT overheating).

Issue:
Just below the top of the trail the Bronco starts to stutter like it's running out of fuel. We stop, try to restart and it almost fires. Try that a couple more times with the same result. Now, I remember I had smelled fuel once or twice on the way up and got out and heard the gas cap hissing. I removed it and a TON of air came out and continued to come out for a few seconds. I listened closer and heard what sounded like bubbling in the tank.

Question:
What the heck happened? I'm guessing it's related to the pressure in the tank. Is my gas cap faulty because it's not venting properly?

I've not had this happen before. Went wheeling the same trail during Labor day but had a full tank and didn't have an issue. I haven't made any changes to the fuel system.

 

[75junebug]

Where is your exhaust exit? Do you have the fuel tank vented? Earlier Broncos didnt have the vented cap system

 

[Ryans71]

The single exhaust exits out the rear & down next to the tank. I felt it and the tank was warm, but not hot at all.

I don't have it vented. There's three ports on the tank. One large one for output to pump and two small ones. I use one of the small ones for the return line and I capped the other.

So I guess I should vent it. Do What's a good way to vent it? Just clamp a hose on it and run it to where? And what do I put on the end of it?

 

[bronconate68]

Hello Ryan, Its good to see you are still out there wheelin. I hope you and your family are doing well. Maybe we will meet on the trail in the near future.

Oh yeah, hope you work out this venting issue, though I know nothing about it.

Nate
'68

 

[ScanmanSteven]

Vent it with a looong hose, maybe routed up as far as the engine compartment. I have mine vented with about 3' of hose with a small filter from parts store on the end. It's stuck up behind the taillight but on steep climbs fuel still runs out. Doesn't make sense but it does. So I'm going to buy new hose and run it forward and up and hope that works. Good luck.

 

[Viperwolf1]

Bubbling in the tank is normal if the return is plumbed in low and the fuel is warm.

 

[Ryans71]

Low compared to the tank or pump?

I used the old fuel line that runs along the drivers side of the frame as my return line.

 

[Viperwolf1]

Low compared to the tank or pump?

I used the old fuel line that runs along the drivers side of the frame as my return line.

Low as in below the fuel level.

 

[Ryans71]

Gotcha ;D, thanks.

Ryan

 

[Ryans71]

Low as in below the fuel level.

Does it continue to bubble if the motor and pump is off?

 

[Viperwolf1]

Does it continue to bubble if the motor and pump is off?

It will for a few seconds. The fuel picks up a lot of heat from the fuel rail when it's under 30-something psi. When it passes the regulator it drops down to almost 0 psi and that causes it to boil.

 

[Ryans71]

It will for a few seconds. The fuel picks up a lot of heat from the fuel rail when it's under 30-something psi. When it passes the regulator it drops down to almost 0 psi and that causes it to boil at a lower than normal temp.

Very interesting, learn something new every day I didn't know gas boils. Thanks.

And now that I think about it, it did happen one more time that day. After the first time we opened the hood, removed the fuel tank cap, and rolled it down to a more level spot. It started. Then we continued on up the trail (still going up hill the whole time) for another 1/4 mile or so. When the trail reached the pass, we went down the other side. Then we got down to where we were going to set up camp I tried to go up a little offshoot trail. I was only on that uphill trail for a few minutes and it happened again. We rolled it down to a sort of level spot and it started.

So now I'm thinking it's a fuel pickup issue. But I can't figure out why I was able to go up hill for a while and it didn't happen. But to have it happen again later. I'm stumped.

 

[Viperwolf1]

What fuel pump setup are you running?

 

[Ryans71]

I run the stock high pressure pump from a ford truck. Fuel moves from tank to through a Fram HPG1 fuel filter to the pump then to the rails via hard fuel line along the passenger frame.

 

[Viperwolf1]

May not be a pickup issue but a pump issue. Using just an high pressure pump works if it's near the tank. They don't like to pull fuel, especially uphill. Those truck high pressure pumps had low pressure pumps in the tanks.

 

[75junebug]

Consider using a low pressure pump mounted close to the tank, feeding an accumulator(BCB and WH sells them) and then have the frame mounted HP pump under drivers area on the frame. I would not trust any of the existing lines that were originally for venting the tank as return lines....
I have a NW 23 gal tank. pickup tube is in the front area of the tank. On the side is the fill nozzle, the 3/4" overfill nozzle and 2 1/4" ports. One of these is the return line(when I was EFI), and the other is plumbed to the plastic vent box on th DS rear fender. This in turn is plumbed into the charcoal canister behind the front DS wheel I very rarely have fuel smells, and never have tank pressure/vacuum issues.