Any idea why the fuel gauge may be stuck on "full"

 

Welcome to the forum

What year Ranger, fuel gauge changed in 1988?

1989 and up used 16 OHMS(Empty)-158 OHMS(Full)

Disconnected wire will have very high OHMS so would show above full all the time

There is also an "anti-slosh" module on the back of the instrument cluster(dash board), and these are a known issue in Fords.

Google: ford anti-slosh module

Although this usually causes Empty reading

There is a Yellow wire that runs from the gauge back to the gas tank, the SENDER/Float inside the tank has a Variable Resistor(like a volume control) attached, as the float goes up and down the resistance changes, from 16 ohms if float is at the bottom(empty), to 158 ohms if float is at the top(full).

Anti-slosh module holds resistance level for 10-20 seconds or so, so when you go around a corner the gas gauge doesn't swing up and down as the float moves with gasoline sloshing around.

You can test yellow wire back by the tank using a OHM meter, to Ground, should read between 16-158 and if you rock the truck the float/ohms should change as gasoline sloshes around.
If ohms are out of that range then sender in the tank is bad, or wires at the top of the tank are

 

Thank you!

 

I'm going to hijack this thread, my 99 3 liter suddenly developed the exact same issue.
Plus I am also getting a P0453 code _ "Fuel tank pressure sensor circuit, high input"
CEL pretty much comes on right away even after disconnecting the battery over night.

Is that sensor located in the tank, I'm thinking that if there is a bad connection for the fuel sender, it's affecting the sensor ?
Probably sharing the same plug, but different connection ?

 

I think the fuel pump/sender wires are separate connection that the pressure sensor/EVAP wiring

Picture here but not sure its a 1999: http://www.explorerforum.com/photopo...own_sensor.jpg

But it is possible that both share the same Ground point

 

Thanks Ron
I'm hoping it's just a bad ground.
The two going out at the same time is quite the coincidence.

I'll pull the box and check things out.
I know the mechanic who put the new fuel pump in forgot to connect up the EVAP line on the tank, so who knows what else I'm going to find.

 

Looked at the 1999 Instrument cluster diagram and the Temp sender and fuel pump sender share a ground, so dash temp gauge working should mean fuel send ground is OK.

Disconnect wire will send fuel gauge to above full

 

Found the sensor, it's integrated into the fuel pump cover, at least it was on this B4000 at the junk yard today.
Tried getting it out too, didn't want to budge, so hopefully it isn't an integral part of the fuel pump assembly.
Shouldn't be though, the sensor is sold separately.

I'll keep this updated when I fond what's wrong.

 

Good news, so far...
Checked the cab/rear wiring harness connections and they were full of what looked like this white lithium grease.

Cleaned that all off with lacquer thinner and applied some dielectric grease.

Fuel gauge works now (so far), and no "Fuel tank pressure sensor circuit, high input" code.

The code would show up right away after a disconnected/reconnected the battery, so there was nothing after start up.

Scan tool shows no stored codes either.