81 FI runs out of gas but 3/4 tank full

[whiterabbit]

Ok, here's one for you. Fill up and drive around till needle is above the half tank mark and it starts sputtering and dieing. Fill up only takes 4 gallons but it then runs fine. I'm scratching my head on this one. Any ideas??
Thanks all.

[So Cal Mark]

I'd remove the sending unit and look inside. the pickup tube may be damaged. Have you tried loosening the cap to see if there is a vacuum in the tank?

[124cso]

Without knowing history of your car, You will (should) not be able to see the pickup in a FI tank. FI car tanks are different from carby car tanks.
The carbed cars seem to have no baffles but the FI tank in mine was well baffled into 5 sections. I had to pull mine out and use a remote video camera (on a metal snake) to actually see the pick-up. A bit like they use for looking down drains etc. or up your u-know !
Have you had the car long, always done it or just developed ? Is bottom of tank damaged ? A crash down on something may have cracked pick-up tube part way up and allow it to suck air ?.

A FI car has the pick-up coming out at the middle seam front right corner (as it sits in the car), return is next to it. Carby car has both going thru sender unit bolted to top of tank, as FI pump is designed to push not suck and so is primed by tank pressure/gravity.

You should not get a vacuum lock as the tank is vented thru to charcoal filter on front left side of engine bay, next to washer bottle.

[whiterabbit]

Had the car for about 6 months. First week it ran out of gas with a quarter tank remaining. Now acts like it runs out at about 1/2 tank. Yea the tank still vents through the charcoal filter. I replaced the 3 legged vapor check valve with a new one from the new parts box that came with the car today. Found loose hose clamp between pump and filter. Tightened it. Pulled the tank cover and the fuel level sender is new and working. Pulled the hose from pickup and ran a wire down it. Clear.
Could the tank be half full of water?

[narfire]

Could the tank be half full of water?

Nope, water is heavier than gas so the car would not start if there was any amount of water in the tank.

I'd try and syphon the fuel out of the tank into a 5 gal. container and then loosen the filler hose at the bottom and drain remaining fuel into a tray. The tank is 10 imperial gallons/ 11.8 us gal or about 45 liters. See what the fuel looks like...rust flakes ? pull the sender see that it moves easily.
When mucking about , do remember to have a fire extinguisher real handy. That way you won't need it
Chris

[124cso]

Could the tank be half full of water?

I'd try and syphon the fuel out of the tank into a 5 gal. container and then loosen the filler hose at the bottom and drain remaining fuel into a tray.

Been there, You should not be able to syphon petrol out thru filler neck as there is a grating at the bottom ( to stop others!).
Use say 12" length of 1/4"pipe/ copper tube fitted to end of say 5 foot of 1/4" plastic hose, pull out sender unit and you should be able to syphon off all but about 1/2 a cup from the tank to container/s on floor behind car.

DON'T FORGET TO DISCONNECT BATTERY FIRST !!!!!!!!!!!!

Not sure what your problem may be. Pickup is ( I figured) fitted to tank BEFORE the 2 halves are welded together. Either that or Fiat used trained mice to work from inside the tank !
Could be a build up of crud around the pickup filter and the fuel needing more and more "head" pressure to get thru ?

You cannot use a slushing compound in a FI tank as it will gum up the filter completely. I had to convert a clean carby tank into a FI tank.

[whiterabbit]

Yea, as soon as I posted about water I realized it would be in the bottom of the tank.(DUHH!)
Thought about it and thought about it. I'm stumped. Pulled the sender and it''s fine. Took a blast proof flashlight and looked in the tank. Clean as a whistle. The large filter looks old so I'm off to Napa today for a new one. The fuel pump is new. PO must have replaced it not too long ago. The rubber bushings are missing on the pump mount and filter mount. Grrrr!
Pressure regulator?

[124cso]

. Pulled the sender and it''s fine.....The large filter looks old so I'm off to Napa today for a new one. Pressure regulator?

If you have a Fuel Injected car, the pickup should NOT be on the gauge sender unit !!!!!!!!!!!!! If it is, THAT is probably part of your problem. You certainly cannot get your hand to the filter to replace it !!!

I can probably put money on it that when you tried the car out, before buying, it had a full tank ???
Pick that's why he sold it ?? Replaced a rusty tank with the wrong one and now the pump loses it's prime ??

As I said before THE TANKS ARE A DIFFERENT PART # on an injected spider.

http://www.flickr.com/photos/67434740@N00/6057842140/

[whiterabbit]

Well then you owe me $$$$$. The car had less than a 1/4 tank when I got it. Had to fill it up to drive home.
It's a FI car with a FI fuel tank and a FI sending unit. The filter is the one mounted inline with the electric fuel pump under the car in front of the rear axle.
Picked up a Napa Gold fuel filter (Wic) today, didn't get a chance to replace it today.

[So Cal Mark]

it could be that a vacuum is being pulled in the tank. When the sputtering starts, loosen the fuel cap and see what happens

[124cso]

Well then you owe me $$$$$. The car had less than a 1/4 tank when I got it. Had to fill it up to drive home.
It's a FI car with a FI fuel tank and a FI sending unit. The filter is the one mounted inline with the electric fuel pump under the car in front of the rear axle.

No I was meaning the gause filter which is mounted on the end of the pick-up inside the tank. It is there as a primary to keep any crap out of your fuel pump. It is superfine (brass i think) mesh sock crimped onto pipe and as I said, you cannot get to it. Been there, done that. Any inline filter problem would not likely to be affected by fullness of tank.

Are all the vacuum lines in o.k condition ? Vacuum from plenum box clears charcoal/carbon cannister and gas tank fumes from all those tank vents and controls fuel pressure relief & flow back into tank.

[124cso]

Just had a thought.
If someone has swapped the feed and return hoses at the tank, it would still run o.k. on a full tank. But as the return line is just a short pipe stub soldered into tank, car would stop as soon as the fuel level dropped to the base of the return stub.

Syphon fuel to say 1/4 full & try swapping them ? If currently on correct lines, it will not run for more than a few minutes.

If it keeps going....................

[danaspider]

I would agree with Mark on this one. I had a similar issue on a Mazda RX7 where in the summer it would loose fuel pressure at about a half tank. Fill it up and it ran fine. Was part of the venting that was clogged and vacume build up prevented the pump from being able to pull gas out. Open the filler when it happens and see.

[whiterabbit]

Hmmm. Feed & return lines swaped? They are diffrent dia. fittings soldered to the tank the larger line is approx. 1/2 dia. and it's attached to the pump. The smaller line I'm assuming is the return and it's attached to the smaller fitting. I did notice the lines had phillip head clamps on the ends while all the other lines from the vents had the crimped factory clamps. I'll investigate into that further.
Don't think it has a vac lock on the tank. My gas cap is kind'a loose. The brass threads on the filler are chewed and the cap is lightly screwed on. ( I sooo gotta' fix that one day) I was guessing that too, that's why I replaced the 3 legged one way vent in the trunk and checked the vapor canister under the hood.
Gonna' put a gas can in the trunk and run her and see if the problem is still there.
Ahha. DUH! That charcoal filter vapor system is only oneway! Pulls vapor from tank ONEWAY! DUHHH!
I'm gonna' look at that gas cap. It's new and I dont see a vent hole in it!

[124cso]

Cannot recall what those hoses are like. It's the middle of the night as I type this so will have a look at mine tomorrow, no it's actually later today I see !
I am sure my gas cap has no vent hole and is probably the original. looks it anyway.

I'm a bit stumped as to what your problem might be !!!

Goodnight