Trying to buy the fuel sending units(both) for my '89...
 

So I've got an 89 F150 reg cab long bed... I've had it for a few weeks now and the front tank has always read empty even when full... the rear tank WAS working until I filled up today:-X05 Now it's doing the same thing.

Trying to order a couple sending units for my truck, is it possibly to figure out which of the tanks I have? It appears I will need the rear "after axle" tank regardless, but the front can be either a 19 or a 16-17 gallon tank(looking at www.rockauto.com).

Is it possible to tell by VIN which size my front tank is? Or is the "mid ship" tank size dependent on if it's dual or single tanks?

I'm going to just pull the bed to change both, that won't be too hard with the help of a few friends. I am considering just replacing the fuel pumps themselves at the same time(because I have some stupid luck with stuff like this)... it appears there is a low pressure pump/sending unit/float/strainer in EACH tank, and then an addition inline high pressure pump after the tanks.

I've replaced a bunch of fuel pumps and sending units in other vehicles, but never anything w/ a dual tank setup... is there a diagram somewhere of how this thing works? I know there's some ridiculous mechanical tank selector valve doohickey, just trying to figure out how everything really works in relation to each other.

Its really easy to change. Also, its cheaper to get the pump/sending unit assembly. Ive done this a few times on these trucks. They are also set up with a lock ring holding the sending unit into the tank. All you have to do is disconnect the fuel lines and harness connector, release the lock ring and pull out the sending unit assembly. There are no special tools needed to remove the ring. I use a flat head screwdriver and tap it around but most guys go with a brass drift or the like to avoiding sparking. Ive never had any problems with it. There is nothing complicated with the dual tank setup.

The tanks are really just set up individually and the lines run into a selector valve in the frame rail. Im not really sure what you were asking for when you said a diagram for the setup but it functions just like having one tank but with the selector valve you can switch voltage between sending units and change the fuel flow through the valve (front or rear tank source)

Thanks!

I was mainly wondering about what P/Ns or whatever I may need for the front tank... There are a couple options at the parts store.