I've got an '87 Ranger and my fuel gauge always reads full, regardless of how much fuel is in the tank. I'm going to be putting on a camper shell and lumber rack, and before I get all that on top of the bed I figured I'd get this fixed first since I know I might need to get into the fuel tank to fix it and don't want to take all extra that stuff off. I pulled bed and took out the fuel sending unit to see if the float was stuck - it's not stuck, and moves easily, but while I had it out I played around with it and noticed a couple curious things.

1. When out of the tank, I can articulate the float by hand and the gauge will move (albeit slowly), but it seems to be reversed from how it's supposed to be: float all the way UP shows empty, DOWN shows full.
2. When I put the fuel sending unit back in the tank it goes all the way back up to full, same as before, even though I've got about half a tank.
3. There are some small tears in the fuel filter on the bottom of the fuel pump.

I don't understand how it could read variably (if backwards) when out of the tank but constant in the tank - is it shorting to ground somehow when it's in the tank?

Also, if it's reading backwards, do I need to change a pin wiring somewhere, or do I have the wrong fuel sending unit in there?

Third, I've been looking around and trying to find a fuel filter for the pump and have had trouble finding parts, but LMC has the full fuel sending assmebly with a new pump - do I have to go that far, or can I get parts somewhere?

Any help welcome, I just got the truck a few months ago and am still getting a feel for it.

 

Welcome to the forum

Up thru 1988 Ford used these sender OHMs for all their vehicles
Empty= 73 ohms, float down
Full = 10 ohms, float up

1989 and up
Empty = 16 ohms
Full = 158 ohms

So they are opposite, if previous owner swapped out assembly he may have put in one for an 1989 and up



The delay is from the Anti-slosh module on the back of instrument cluster, and normal
Since float will swing up and down every time you go around a corner or stop quickly, as the gas in the tank "sloshes" around, this module delays instant changes, so what you see on the gauge is like an "average" of the fuel level

 

Very helpful, thank you. I also just found that the float fills with fuel, which with this information totally makes it click - the float fills with fuel, sinks to the bottom, which would read empty normally, but with a newer than "89 sending unit with reversed resistance readings it's showing full all the time. That makes me think I should just replace the sending unit altogether with one from the correct year, since I at least need a new float and resistor. Any idea if the ones from LMC come with a new fuel filter for the pump too, since that's also shot? I'll also need the O-ring/gasket for the sending unit, not clear from their website if it comes with that. I'll just give them a call tomorrow, thanks again!

 

Thinking more - does that also imply I need to replace the fuel pump? Will the one I have be compatible with the new sending unit?

 

It depend on what previous owner did
1986 to 1988 fuel injected Rangers had two fuel pumps
Lift pump(7psi) in the tank and High pressure pump(40psi) in the drivers side frame rail by the filter

1989 and up got the high pressure pump in the tank, so just the one fuel pump
IF..............previous owner did the high pressure one pump setup then switching back would mean you need to add back the 2nd pump in the frame rail
So have a look, can't miss it, looks like a tube with 2 hoses and wires

If that's the case then might be easier to just add a 16-158 ohm gauge under the dash

 

Thanks again for your help Ron. I did have the two pump setup, but both are working just fine, so I got a new fuel sending unit from LMC without a pump, installed it, and I've got a working fuel gauge!

Joe