Fuel Sending Unit Defective 1959

[Cadillac Nut]

I got my '59 flat top up and running after years of being off the road.   Carb and fuel pump rebuilt, lines cleaned, new hoses, new gas tank, new fuel sending unit (from Auto City Classic)   Car runs great off a gas can. But it will not pull gas from the tank.  I have narrowed it down to the fuel sending unit.  When I disconnect the fuel line at the tank and put it in a can of gas, it runs fine.  It's an A/C car and the vapor return line is working. Yet will not pull from tank.    The new fuel sending unit must be defective.  Has anyone else ever run into this?  Yes, there is plenty of gas in the tank.    How I hate having to do the same job over again.......

Garrett

[55 cadi]

Doesn't the fuel sending unit only send voltage to the gauge on how full it is, it doesn't actually send fuel, there is a wire attached to it that goes to the dash gauge.

[Coupe Deville]

I have been here before. If you disconnect the line from the tank and pull a vacuum on it, and only air comes out, then the problem is the sending unit pickup tube. A dirty way of doing this is disconnecting the line from the tank, put piece of fuel hose on the sending unit line, and suck on it with your mouth.. If your getting gas, you can rule it out and know for sure the sending unit is not at fault. Also, make sure that you have not switched the fuel supply, and fuel return hoses to the sending unit. If they are backwards the fuel pump will be sucking air.

55 cadi, not sure what years were different but 1959/1960 the sending unit had the fuel supply/return lines built into the sending unit itself, to make everything one unit. Here is a example. Not my picture.

-Gavin

[55 cadi]

Ok  my mistake, I have sen a few years and they didn't have that on them, must not have seen those years.

54,55,56 and others I have seen don't have those tubes on them.

Jason

[Coupe Deville]

Yeah, I guess they figured that making the fuel pick up/sending unit one singe piece, it would be easier to service as a unit. My 57' Cadillac didn't have the tubes on it ether. Neither does my dads 41' Dodge. Sending unit is its own piece.

[Cadillac Nut]

Yep, that is the fuel sending unit I have in your photo.  I double checked the lines are connected correctly.  Something is wrong in the pick up tube.   It runs fine when I put the fuel line in a gas can.  Very strange...

[gary griffin]

Time to disconnect the supply and return tubes and clean out the tubes in the pick up unit I think.

[savemy67]

Hello Garrett,

In the photo provided by Gavin, there is a strainer (aka sock) attached to the bottom of the fuel sending unit.  Did your replacement fuel sending unit come with a new strainer?  Check that the strainer allows fuel to flow.

My '67 has a vented fuel tank.  In addition to the line to the pump, and the vapor return line, there is a third line at the front of my gas tank that is the vent (see attached photo - vent line is in middle of photo, fuel and vapor return lines are in upper left corner).  I don't recall if a '59 has a vented tank.  If so, check the vent hose for blockage.  If not, check if your gas cap is vented.  Good luck.

Christopher Winter

[59-in-pieces]

Garrett,
As you likely know, if you dropped the gas tank or saw the front of it while you were under the car, there is a vent for the tank, and therefore a vented gas cap or not, the tank can not develop a vacuum to stop fuel flow - see pics.

Two thoughts came to mind - but before doing either, check to see the level of fuel registering at the dash board if empty = sketchy for tests, 1/2 full or better give the tests a try.:

1. Are you sure that the sending unit you bought (assume you bought one) was correct as to the length of the pick-up tube, on which goes the sock.  If too short (like one size fits all parts, not specifically 59 Cad) - not OEM length, the fuel level would need to be higher in order for the pick-up line to work.  This may explain why the line does not pick-up from the tank, and why on the other hand if the line is submerged in a can of gas, it does work.

2. Have you removed the tank to determine if the tank had been previously coated from the inside because of rust.  Often the pick-up screen - sock - gets clogged by rust or floating pieces of coating material - so fuel pump pulls a vacuum and no gas flows to the engine.  These floaters don't necessarily cause a full blockage, but could cause reduced flow or intermittent blockages - concurrent with the splashing of the moving fuel.  If rusty or floaters, replace the tank (re coating the inside = likely chasing your tail later).

Gavin's 'dirty approach" is a good one if you try to suck on each line, separately - one line being the supply to the motor with gas in your mouth (= pick-up line low enough) & (no gas in your mouth, gas pick-up too high), or with the other line with air in your mouth (= the vapor return line).
Good luck - don't swallow - have fun,
Steve B.

[Cadillac Nut]

Hi  Guys,
Thanks for the ideas.  The fuel tank is clean, it is brand new, from Auto City classic.  So is the sending unit.  It's just like the one shown in Coupe Deville's photo.  I am assuming these have the correct length pick up tube?  Anyone else bought one of them from Auto City Classic? 
The vent tube in the back is clear.  I was getting a reading on the fuel guage, about 1/4 or so.   Auto City send me a new sending unit after I talked to them.   So I will be installing that.   Is it normal for the vapor return line to return gas to the tank?

Thanks again,
Garrett

[390 man]

It could possibly be a fuel pump issue. I had a problem with a 61 Cadillac. It also had a rebuilt fuel pump, but the valves were installed incorrectly from the rebuilder. Both valves were facing the same way into the fuel chamber of the pump. I don't know how but somehow it ran. This could explain why its runs off from a can. It would be easy to check. Just pull the top cover off from the fuel pump and look inside. 1 valve will be face down, other will be faced up.

[76eldo]

Tri Power and AC cars have the return line back to the tank.

I have a new tank and sender sitting here for a 60 I am working on.  I won't be installing this for at least a month or two.  Hope it works.

Brian

[Cadillac Nut]

Thanks.  Fuel pump looks ok, here's a pic of it (when it was dry, before I first started the car).  Tomorrow going to change the sending unit....

Garrett

[Scot Minesinger]

Remember Washburn's wall of shame reference when this happened to him, it was a section of crushed fuel line on the wall.  Just to be sure, and I know you may have, visually examine the fuel lines from carb, thru pump back to tank.  Make sure that in no place are they kinked or crushed - double check this.  The pick up is likely a little more restrictive than the rubber hose in a can of gas and may make the difference to allow for a kink or rushed section.  I agree it is probably the pick up or sock.

To test for the sock, remove gas cap and blow compressed air in careful short bursts from pick-up side out side of tank so air passes thru sock and dislodges any particles that may be clogging it.  Then reconnect and start car.  If it runs, that is it.

[Cadillac Nut]

Well I removed the tank and changed out the fuel sending unit.   About 5 hours later I now have a '59 that runs great, no issues.  The fuel sending unit was defective, the sock had come off too.    Another case of, "just because the part is new doesn't mean it's any good"

Garrett

[Scot Minesinger]

These new parts all mostly terrible.