Gas Tank Vent line (and other) questions
01-26-2009, 04:34 PM
#1
Staging Lane
Thread Starter
iTrader: (1)
Join Date: Nov 2005
Location: Huntsville, Alabama
Posts: 62
Likes: 0
Received 0 Likes
on
0 Posts
Gas Tank Vent line (and other) questions First, my setup:
1979 Malibu
1987 Monte Carlo EFI tank
1987 Monte Carlo EFI sending unit and pump hanger
High pressure in-tank fuel pump
Picture of setup how I have plumbed:
Top is output line
Middle is return line
Bottom is vent line
OK, I have a few questions:
First, is there anything special about a EFI gas cap? In other words do I need a gas cap for a EFI setup or, can I just the run the stock '79 gas cap?
Can you just plug (close off) the vent line on the sending unit or does it need to be allowed to "breathe"?
The reason I ask is that I tested the in-tank pump this weekend. Right now, I just have a piece of hose hanging down (temporary) for the vent line. When I turned on the pump, it started shooting fuel out of the vent hose. I'm 99% sure I have everything connected properly. The output (feed) line already had a special fitting on it to distinguish it from the return or vent lines. Any ideas why it would have shot fuel out of the vent line?
1979 Malibu
1987 Monte Carlo EFI tank
1987 Monte Carlo EFI sending unit and pump hanger
High pressure in-tank fuel pump
Picture of setup how I have plumbed:
Top is output line
Middle is return line
Bottom is vent line
OK, I have a few questions:
First, is there anything special about a EFI gas cap? In other words do I need a gas cap for a EFI setup or, can I just the run the stock '79 gas cap?
Can you just plug (close off) the vent line on the sending unit or does it need to be allowed to "breathe"?
The reason I ask is that I tested the in-tank pump this weekend. Right now, I just have a piece of hose hanging down (temporary) for the vent line. When I turned on the pump, it started shooting fuel out of the vent hose. I'm 99% sure I have everything connected properly. The output (feed) line already had a special fitting on it to distinguish it from the return or vent lines. Any ideas why it would have shot fuel out of the vent line?
01-26-2009, 04:45 PM
#2
Are you sure you that the vent line isn't acually a second feed line? Or did any even come with dual feed lines?
Anyways, I am not sure exactly how well those "breathable"/vent gas caps are, and the tank definately needs to breathe, so I just vented it out to behind the rear bumper.
In order to prevent gas from having any chance of flowing up into it and out the vent filter, directly after the vent tubing leaves the sender, I bent it up almost vertically, up into the hump for the rear axle about 10", then bent it back down and around the tank to behind the bumper, through a valve cover filter.
Anyways, I am not sure exactly how well those "breathable"/vent gas caps are, and the tank definately needs to breathe, so I just vented it out to behind the rear bumper.
In order to prevent gas from having any chance of flowing up into it and out the vent filter, directly after the vent tubing leaves the sender, I bent it up almost vertically, up into the hump for the rear axle about 10", then bent it back down and around the tank to behind the bumper, through a valve cover filter.
01-27-2009, 06:22 PM
#4
I think in order for the hanging hose to flow gas out, if would 1) have to have the inlet for the breather in contact with gas (tank filled up way to high??) and 2) would have to have some initial gas flowing thru the hose in order to develop the "momentum" of the fluid flowing out.
Just think of a gas syphon, the tube inlet has to be submerged and you have to start the flow some how (pump or mouth if desperate!).
I would get yourself a decent-sized container, stick the vent hose end into the container but make sure it is above the top of the tank, then turn on fuel pump. It will spurt or something if it is just a pressure inequality issue, but if it keeps flowing a lot of gas out the vent tube, I'd say it'd have to be hooked up to the pump output line.
Just think of a gas syphon, the tube inlet has to be submerged and you have to start the flow some how (pump or mouth if desperate!).
I would get yourself a decent-sized container, stick the vent hose end into the container but make sure it is above the top of the tank, then turn on fuel pump. It will spurt or something if it is just a pressure inequality issue, but if it keeps flowing a lot of gas out the vent tube, I'd say it'd have to be hooked up to the pump output line.
01-28-2009, 04:38 PM
#5
TECH Enthusiast
iTrader: (4)
Join Date: May 2004
Location: council bluffs Iowa
Posts: 565
Likes: 0
Received 0 Likes
on
0 Posts
You need to run it up to the highest point with a good length of fuel rated line, as you already have, and you need to put a small k&n filter on the end of it, in case of back flow.You dont want to contaminate your fuel. Some people run tip over valves here but I tried this and had it perfectly vertical but when I tried to fill up It would not accept gas no matter what. I had it in correctly I checked it 7 ways to Sunday. So I had to remove it, and just run the filter.
