New fuel tank and sending unit weirdness (Questions)

[Rembrant]

Gentlemen,

I installed a new fuel tank this past winter (Spectra Premium # F14A 16.5 Gallon), and a brand new sending unit (Spectra Premium FG75A). I tested the sending unit before I installed it in the tank, and it stroked the fuel gauge with no issue. So now for the past few weeks driving the truck, the gas pump cuts off and the fuel gauge only shows 1/2 tank. I don't know how much fuel is in there...I drive it until I hits Empty, and then refill it...today it took 8 gallons.

Previously, the old rusty tank and sending unit both worked fine. I could fill the tank until full, and the gauge worked perfectly.

So today I got wondering if I tried to gently force some more fuel in there, if it would actually take it. I got another half gallon in there maybe, without trying any further, and the gauge went a bit above 1/2 way on flat ground, but when I was going downhill or coming to a stop, the gauge would read almost full. Back on level ground it would go back to the mid-tank level or so.

Anybody know what's going on here? Should I try to force feed it a little more fuel again and test?

That leads me to my next question...if that does work, then what is wrong?

I reinstalled the plastic tube in the fuel filler hose (reused original hose). I just checked and it is still intact on the upper end. When you look down the hole, all you can see is that plastic tube.

The reason I am asking all this is, I'll be pulling the box off on Tuesday before sending the cab/chassis to the body shop, and if I need to do something with the tank and/or sender, etc that would be the opportune time.

Does that plastic tube really need to be in there?

What would stop the tank from filling higher (if indeed that is the problem)?

Or, is there just something wonky going on with my new aftermarket tank and sender?..

[ArdWrknTrk]

You might consider going with a later (Bricknose) fill assembly.

They reverse the vent and fill tube.

As for your sender... Idkwts.

It's a shame it won't read right when mounted in the tank.

Is it Motorcraft, or Chinese?

[Steve83]

I'm not a fan of Spectra or Airtex, but I don't think the tank or sender is causing this problem. Generally, filling problems are caused by the neck vent collapsing, or being kinked or out-of-place. There should have been a steel support in the tank's fill nipple to keep the bottom of the vent tube up where it belongs. Did you insert the tube into that support?

In any case, my first instinct is always to upgrade with newer (generally-better) parts. The '87-96 filler neck is a direct replacement, with better venting (both in the neck & the cap), and better caps (tethered, if the grommet survives; and more ergonomic).

https://supermotors.net/getfile/285175/thumbnail/fillernecks.jpg

https://supermotors.net/getfile/1147366/thumbnail/captthr.jpg

[Rembrant]

There should have been a steel support in the tank's fill nipple to keep the bottom of the vent tube up where it belongs. Did you insert the tube into that support?

There was a little loop there for it yes, and yes I did insert the plastic tube in there.

It never occurred to me to check the later trucks for a filler hose...I never see them in the junkyards or being parted out. I'll check around and see what I can find. With my truck being a Flareside, the styleside fuel filler is not a direct fit...they are different. Maybe the 92-up Flareside filler will work if I can find one.

In any case, I'll check the vent tube and make sure it is all OK.

 

[ArdWrknTrk]

I'm not a fan of Spectra or Airtex, but I don't think the tank or sender is causing this problem. Generally, filling problems are caused by the neck vent collapsing, or being kinked or out-of-place. There should have been a steel support in the tank's fill nipple to keep the bottom of the vent tube up where it belongs. Did you insert the tube into that support?

In any case, my first instinct is always to upgrade with newer (generally-better) parts. The '87-96 filler neck is a direct replacement, with better venting (both in the neck & the cap), and better caps (tethered, if the grommet survives; and more ergonomic).

https://supermotors.net/getfile/285175/thumbnail/fillernecks.jpg

https://supermotors.net/getfile/1147366/thumbnail/captthr.jpg

Steve, my '87 came with the gray strap tether.

I 'upgraded' to the black caps with grommet retainer, from Amazon.

Motorcraft number FC 920 and MY Amazon price is $9.80.

The biggest difference is that the later fillers fuel goes down the tube and pressure vents annually.

With the bullnose fillers gasoline goes around the vent and the tube inside vents up the middle.

[FuzzFace2]

There should have been a steel support in the tank's fill nipple to keep the bottom of the vent tube up where it belongs. Did you insert the tube into that support?

There was a little loop there for it yes, and yes I did insert the plastic tube in there.

It never occurred to me to check the later trucks for a filler hose...I never see them in the junkyards or being parted out. I'll check around and see what I can find. With my truck being a Flareside, the styleside fuel filler is not a direct fit...they are different. Maybe the 92-up Flareside filler will work if I can find one.

In any case, I'll check the vent tube and make sure it is all OK.

Cory, you are right on the style side & flare side fillers being different.

The front tank on mine was a miss match of parts when I go it I just used parts to make it look nicer.

For the rear tank I can remember what all I used but again I used what I had and to make it look nice.

On the front 16 gal tank are you sure you got the right sender?

I ask because most list the same sender for both the 16 & 19 gal tanks and this is not right.

I have yet to test mine, well put 5 gal. of gas in the rear tank and it did move the needle hope to do the same on the front tank today.

Dave ----

[Steve83]

...the styleside fuel filler is not a direct fit...they are different. Maybe the 92-up Flareside filler will work if I can find one.

Yes, I should have said for the same body shape & tank position. I can't remember if dually filler necks are interchangeable with stepsides, but it's worth checking.

[grumpin]

...the styleside fuel filler is not a direct fit...they are different. Maybe the 92-up Flareside filler will work if I can find one.

Yes, I should have said for the same body shape & tank position. I can't remember if dually filler necks are interchangeable with stepsides, but it's worth checking.

If it’s not the vent, take a couple of gallons with you and run it till it’s empty, then see how much it takes to fill it.

[Rembrant]

If it’s not the vent, take a couple of gallons with you and run it till it’s empty, then see how much it takes to fill it.

Hey Grumpin good idea. I will give that a try as well.

[85lebaront2]

...the styleside fuel filler is not a direct fit...they are different. Maybe the 92-up Flareside filler will work if I can find one.

Yes, I should have said for the same body shape & tank position. I can't remember if dually filler necks are interchangeable with stepsides, but it's worth checking.

Steve, the dually filler necks are actually very stubby so you may be correct, the bulk of my filler system is molded rubber hoses.