Brinella

DUB

I am having a hard time trying to understand what you are saying. So when you 'run out of GAS'....you can only put in 9 gallons and that is it???

When the tank is full and it gets to 1/2 tank the engine dies???

Do not get in the habit of adding more fuel when the nozzle clicks OFF. if you do.... you are asking for trouble in possibly and more than likely damaging your vapor return system due to it is now sucking in raw fuel. Which siu it now supposed to do....BUT do as you wish.

DUB

Brinella

DUB

Something may be wrong with your sending unit or the fuel pick up on it.

I know if your were in my shop for this problem would have to siphon out all of your gas when the tank is FULL and then see what the gage shows. Then slowly begin to add fuel back into the tank now knowing ACTUALLY how much fuel your tank holds. Regardless of what any book may say.

I would have already removed the sending unit to make sure I have all the gas out and nothing is floating around inside the fuel tank. and manually test it by moving the float and see if the gauge matches where I position the float. Obviously I have it connected to the cars wiring at this time.

IF that checks out OK. I put the sending unit back in and put a few screws back in to hold it.

I connect a hose to the large 3/8" tube on the sending unit and this is where I will connect and use my hand vacuum pump later with the bottle provision that can be used to bleed brakes. NOW I also have CLEAR tubing that I can attach so when I use the vacuum pump in the later step I can actually see fuel in the hose BEFORE it makes contact with my hand vacuum pump. Just make sure the hose is long enough to do this.

While adding the fuel, I will put in ONE gallon. Keeping in mind I want the car LEVEL. Then use my hand vacuum pump and pump it and see if it draws up any fuel If it does not....then add HALF A GALLON of fuel and repeat this step. I keep doing this until I know how much fuel MUST be in the tank for it to flow fuel. While doing so,...I am also watching the fuel gauge so see if it corresponds to what I am adding back in. So if you had 20 gallons in the tank then 5 gallons should make the gauge read about 1/4 of a tank...then add another 5 gallons and so on.

IF I am not mistaken the 'LOW FUEL' light up on the right side of you gauge cluster should come on (if it is working ) when you have about 3 gallons of fuel in the car.

It is possible that there is a hole in the tube of your sending unit that will draw in air much like how a soda straw will do if the hole in the straw is above the soda you are trying to drink.

if you get your sending unit back out I would measure the depth of the fuel tank to where the sending unit seals and then measure the length of the tube that the filter sock is attached to and see if they correspond or not. I m NOT concerned about how long the filter sock is. I want to know where the end of the steel tube that the filer sock attaches to is.

This goes without saying but when you are messing with fuel. COMMON SENSE and SAFETY are paramount. So you are on your own on how you do it if you do any of this at all.

DUB

mark79,80

if you are saying it only takes about 9 gallons to fill the tank to the top, then the rubber liner in the tank may have collapsed. You could try siphoning out all the gas and see how many gallons you can remove. If it is only around 9 gallons. Then look in the tank with a mirror and flash light to see if the liner has collapsed.

bmotojoe

I know 1975-1977 had the rubber bladder, but didn't they go to a hard plastic liner after 1977?
It could have collapsed but removing it through that smaller sending unit hole would be almost impossible.

mark79,80

DUB

The fuel tank does not have a serviceable bladder like some of the 1975-1977's do.

Why it is only allowing 9 gallons is an unknown until the OP gets back with us on this.

There is one possibility and that is that the plastic molded liner that is in the fuel tank got sucked in due to vacuum due to the fuel cap not being correct and the actual liner pulled inwards and is now not going back to the shape it was originally thus allowing more fuel to be put in the tank. This would only occur if the adhesion of the plastic liner gave way from the tank and the fuel tank vapor line connection got plugged going to the top of the fuel tank BUT yet the vapor line that is on the sending unit was still functional...and the fuel cap would NOT allow air to be drawn into the fuel tank..

DUB

The13Bats

While many times this type issue is a gauge or sender in this case we have a major clue the tank will only hold 9 gals so it wouldnt be much reach to wonder why the tank can not be fully filled,
I too thought from first reading his post it has to do with the liner,


Hah, i used the search feature,
I do believe we have a winner,
Check out pauls reply,

tank bladder

L-46man

yup.....symptoms follow this!

DUB

I have not cut apart a 1978-1982 fuel tank BUT I have on a C4 and I can say the liner in it is about 3/16" to 1/4" thick plastic. I have a 1978-1982 fuel tank for testing and fitting purposes and I am not cutting it to prove a point here. So unless there was something really wrong or it was made differently in earlier years. It is possible like I mentioned where it can get sucked in.

This type of liner is no where near as flexible as the other link provided where it is for an earlier car as we know. And knowing that the rubber bladders for a 1975-1977 are an actually service part due to not beign made into a part. They can be replaced if they were still being made. But the plastic liner in the 1978-1982's is a part of the fuel tank so it can not be serviced. You have to buy a new gas tank. Which those that are made today DO NOT have this plastic liner in them.

DUB

The13Bats

Going with info the op provided,

Physics apply if a tank should hold 20 some odd gals and only holds 9 something is preventing it from filling as in something else taking up that tank space.

Bladder, liner, the remains of j hoffa i have no clue.

sambrand

just put a camera there, after all it might be full of gold dubloons hidden away by blackbeards great great grandchildren, or it might just be a collapsed bladder/liner

https://www.walmart.com/ip/Whistler-...RoCwiQQAvD_BwE

sambrand

heh I poked fun at dub, sry pal, couldn't resist!

The13Bats

Yeah, nice follow up to mine

DUB

No offense taken,

The 'ball' is in 'Brinella's' court so it is up to him to do some investigating on this.

Hopefully he comes back with some feedback on what he has found.

Other than that..I have said all I can say on this. A unique scenario that has been mentioned is possible but I feel he would have seen them when he replaced the fuel sending unit initially.. Waiting for his response.

DUB

The13Bats

I see no way to argue if a tank holds over 20 gals runs empty where engine dies and then at pump only holds 9 gals
something is taking up tank space even if some weird anomaly of gas itself taking up that space which isn't very plausible with info given,
While i get the whole what type tank should be in the car who knows what is in there, lots of things can and do happen to a car in decades, hah perhaps it has a 9 gal tank, we just dont know yet,
In front of me i could tell you in 5 mins whats up just like lots of gear heads could,
So im with you i cant wait to hear what an inspection of the tank uncovers, the suspense is killing me, i hope it lasts.

Brinella

Doug1

Glad it's fixed!!

If it was just the sending unit arm being bent, then why was the car running out of gas and sputtering etc.?

Brinella