which fuel sending unit do I need???

[rscustomrods]

So I have a total of six gas tanks now, which have all come out of 1978 chevys. However, some have three tubes coming out of the top of the tank and some have two. I really dont see the need for the third tube, but wanted to find out if anyone knows the purpose of the third tube and if i need it. I plan to purchase new sending units, even though these seem to work. I have the cab off right now and do not want to have to drop the tanks when the truck is complete if these sending units do not work correctly.

Can anyone offer any advice on what to buy? Rock auto has both the two tubes and the three tube styles. Thanks for the help.

Rich

 

[crazy4offroad]

3 tubes = 1 for tbi feed, 1 for return line, 1 for vent.
2 tubes = 1 for carb feed and 1 for vent.
Hope this helps!

 

[rscustomrods]

thank you! that makes total sense. I am running a carb so i will go with the two tube. Thanks again!

 

[Jims86]

3 tubes = 1 for tbi feed, 1 for return line, 1 for vent.
2 tubes = 1 for carb feed and 1 for vent.
Hope this helps!

3 tube is not necessarily TBI only...alot of trucks came with return lines from the pump, like mine did. the 3/8 is the main feed line.

 

[T-ROD]

3 tube is not necessarily TBI only...alot of trucks came with return lines from the pump, like mine did. the 3/8 is the main feed line.

just like jim said there is alot of them that have 3 tubes, the 3/8in. Line is main fuel, and return line, then the third line is for the vapor canister as a vent tube.

 

[89Suburban]

I pulled the pump out of my TBI Burb last weekend. It has four tubes.

Fuel feed
Fuel return
Canister line
Vent hose to filler line

 

[T-ROD]

Yea, that is true, some do have 4, most are three, but yea I almost forgot, they had a few, Im pretty sure the four is for tbi but im not 100% sure.