New Sending Unit and No Fuel

Quick question for one of you out there...I'm not all that great with these things, so I apologize for sounding idiotic...

I recently replaced my fuel sending unit on my 73 cj5 becuase I narrowed it down to an electrical issue there...after buying a unit from quadratec, I noticed that there are two fuel lines going out of the top of the sending unit...one that dips into the fuel, and one for ?. I connected the new fuel line to the one outlet that is deep in the fuel tank and left the one in question open. After I thought that it was being fed properly and I reattached the tank, the engine ran out of fuel. I pulled my fuel line next to the tank off and it was dry as a bone. Ive tried getting fuel to the carb with no luck...Did I miss something? When installing the sending unit, I attached the filter in a snug fashion and carefully put it into the fuel. Im trying to avoid pulling the tank off again and Ive exhausted my efforts...any advice? Thanks for all your help...

Chris

 

Is the pump electric? Is the pump working?

 

The fuel pump is working and has been...the CJ ran fine before I pulled the original sending unit...the only problem was that it was not sending an electrical signal to my speedo...hence the need for an all new sender. The sending unit doesnt seem to be "sucking" the fuel into the fuel line...it ran for a few minutes, but just on the remainder of fuel in the lines after the sending unit change. It seems that the lines are totally dry now (nothing in the engine fuel filter or fuel hoses) and no fuel is being brought from the tank into the lines...did I put the sending unit filter on too tightly? Im at a loss...

Thanks,
Chris

 

You have done one of two things,
You ether have the fuel supply line (Suction) hooked up to the tank return fitting,
In which case you are sucking air out of the tank instead of fuel,

Or you have cracked the fuel supply line neck where it goes into the tank, and you are sucking air!

If you take a close look, you will find the two fittings are slightly different sizes, and you should use fuel lines accordingly.

You should PLUG the vent line if you don't have a vent/roll over valve to the tank... (Vented Gas Cap Models),

And you should MAKE SURE you haven't pinched the fuel lines on top the tank and have your fuel (Suction) line connected to the correct fitting.

The easy way to tell is,
Simply use some CLEAN fuel line, and blow into each of the nipples on the tank.
Where you blow bubbles will be the Fuel Suction Supply fitting,
Where you DO NOT blow bubbles is the vent/return line connection.

Just a silly quesion,
Did you put the 'Sock' on the end of the suction tube that went inside the tank?

That filter 'Sock' is also what reaches the bottom of the tank,
Otherwise you will 'Run Out' of gas at the suction line inside the tank when you still have about 1/3 a tank of fuel.

If you didn't put the 'Sock' on the end of the suction line,
You will need about 1/2 tank of fuel to get things working, and somewhere around 1/3 tank, you are going to 'Run Out' of fuel...

The 'Correct' way to do that 'Sock' filter is to install it on the hard line that goes to the bottom of the tank,
Leave it kind of pushed down on the line.
Then see GENTLY if the filter reaches the bottom of the tank before you get the fitting seated on the top of the tank...

You want the 'Sock' to reach the bottom of the tank about the same time the tank fitting seats at the top.

If you slide the sock too far down, it will be bent in the tank, and won't last as long,
If it's too far up the tube, it won't reach the bottom of the tank and you will run out of fuel before the gauge reaches 'Empty'...

Help clear things up?

 

First, the second connection on the sending unit is for fuel return if needed, can be capped if not used. The pickup tube filter only slides on about a half inch, if you slide it all the way on and it has a flat end it could block the pickup tube. Other causes of fuel starvation would be air leaks in the connections, this will make fuel pickup difficult for the pump.

 

Thanks,

I did slide the pickup tube filter as far as it would go, so ill back it off a bunch. Im getting power to the unit (circuit tester revealed good connection), but the lines are still dry. Ill check for air leaks in the line, but everything seems to be dry. Does the engine have to run to "suck" the fuel into the lines? Im trying to figure out how to introduce the fuel back into the entire line since it ran completely dry.

again thanks for all your help.

Chris

 

If your fuel pump is good, and there are no obstructions in the line between the tank and the carburetor, and there are no air leaks in the line between the pump and the tank, the pump will prime the lines on its own.

Usually it takes a lot of cranking to prime the line if it is dry. The usual strategy is to put a little fuel down the carb and start the engine on that. With the engine running, the line will prime much faster. It may take 2 or 3 tries to fill the lines and the crb float bowl so the engine will run on its own.

If you have the air cleaner off and pour gas down the carb, the engine may backfire and light the gas on fire. If this happens, don't panic. Keep a big towel or other rag nearby and smother the fire. Typically you can beat the fire out with a swipe or two of the towel. If you worry about this, put the air cleaner back after you pour gas in the carb. The air cleaner will smother a fire if you have a backfire.