My 87 iroc has busted a couple fuel lines ( suspected to be something with the pump putting out excess pressure, but thats just a guess) as my charcoal canister is filling with gas and overflowing. Can someone help me with which fuel lines go where as they leave the tank? I have accessed my fuel pump from the top of the trunk area, but i think the lines may be mixed up, possibly causing me to hook up the lines wrong. How can i determine which fuel lines are which and how they hook up to the pump. I need to have the lines replaced this summer. Thanks

My first post - project in progress for almost 2 years...

After engine upgrade and TBI to Carb conversion, I also have a problem that may be related to fuel lines. I understand there are three lines - a supply line (which should be fed by the fuel pump), a return line and a vent line (which goes to canister)

Mine is '88 IROC Z 406 SBC with Rochester Quadrajet. I disconnected power to tank fuel pump (cut wire) & installed low pressure pump in-line under car - so I'm pulling fuel through the old fuel pump. I plugged the return line, and simply put a fuel filter on the end of the vent line to keep debris out.

Problem is - car runs out of gas after using about 10 gallons. I thought vaccuum might be building up in tank - removed cap - no vacuum present. I changed fuel filter - no help - still runs out of gas.

When I installed engine I researched and THOUGHT I'd chosen the "right" line, but now wondering if I have plumbed the carb to the "return" line? Help !?!!?

10 gallons of fuel weighs about 60 lbs which is helping the inline pump overcome the pressure drop across the intank fuel pump.
The supply line is 3/8", the return is 5/16".
Temporarily swap lines; use the return for the supply and ensure the stock filter is before the inline pump, it would also be wise to install a finer filter (10 micron) before the stock filter (40 micron,) because the return line in the tank has no filter sock on it.

If it can now use more than 10 gallons then you know it's the intank pump that's adding restriction that the inline pump can't overcome without the additional pressure of the weight of the fuel. Inline pump must be level with or below the bottom of the tank.
Also the efficiency of the inline pump is reduced with increase in temperature because it's not surrounded with fuel to keep it cool, especially if it's in the engine bay.

Reconnect the TBI intank pump and add an adjustable fuel pressure regulator to lower the pressure to 4-6psi and connected the outlet of the reg to the return line.

Thanks "R" - you might be on to something with your thought about the 10 gals helping pump to lift fuel "up-and-over the top". It seems I have the proper lines - I disconnected main line and attached a hand pump to all three lines. I was only able to draw fuel from the line I thought was main. The measurements you provide seem to match up.

I connected 12VDC directly to the main pump wire under back seat carpet but hear no noise / no fuel - therefore I fear the tank pump is shot. I'm sure I've got the right wire since I'd previously cut the gas gauge wire by mistake. Ground wire has continuity to body. From prior work underneath I don't recall seeing any kind of fuse where wiring exits body to tank.

I'm about to bite the bullet and cut a hole in the body to get at the pump unit so I can see what's going on. I realize this is a short cut, but this car is a "driver" (with many problems) - not a "show car" - so hold the emotions please on this approach.

Car ran out of gas again the other day, gas guage still showed 1/4 full, yet car took only 8.9 gallons at the gas pump - other ideas anyone?

Mark