So bought the truck in December, been doing some minor repairs; and had everything working (except the delayed oil gauge).

But I noticed once in a while the fuel gauge would be off, like I'd park at night with 1/2 tank, go to work in the morning with nearly full tank (I know I ain't lucky enough to get a visit from a gas fairy!) I blamed the temp changes; and it seemed to go away.

Now the last few weeks the gauge is way off. Fill up it's over Full, and stays there for ~100 mi. At about 200mi & 3/8-just short of /2 tank I filled up, took 16.5gal (so ~3gal left).

I connected my ScanGuage (An odbii reader) set to read fuel level, and it's just blank; so I'm guess ing this truck doesn't send that info on ODBii, or I need to tweak the settings.

So I start searching here, and all the posts say to pull a yellow/white wire near the tank, under the drivers door. When I crawl under there, all I see is a pair of connectors, in a Y shape, behind a plastic bracket. Some kind of wires going to what ever is in front of the fuel filter (little old master cylinder looking thing).

I also took the cluster out, pulled the anti-slosh unit out.

I obviously didn't find the right things to short because it never went to empty. with the anti-slosh unit out it read ~1/2 tank. I put an ohm meter on the R's in the unit, I think they read 1k, 3k, 500 (R1, R2, R3).

I think I have all the tools necessary to test everything outside the tank; I just don't know where to stick them!

Does anyone have pics/youtube of how I need to test? Was the big block of wires under neath the correct set to try to ground the yellow/white (top left wire)

Thanks for any help

Just found a video for a 90 SHO, says to cover the 3 terminals & short the 2 on the slosh unit, Did that and it dropped to 1/4 tank. Still covering the 3, un shorted, read just under 1/2.
Key on/run Over full (pegged?), Key off, ~1/8 under full.

 

If you want to try testing the system, stop by radio shack and buy a 50, 100, and a 150 ohm ¼ watt resistors (about $2.00). Pull the connector next to the tank. Turn the ignition to run, and find the Yellow with White stripe wire and insert in turn each resistor between the Yellow with White stripe wire and chassis ground while watching the fuel gauge. If the gauge reads near empty (50 ohm), half (100 ohm) and full (150 ohm), the gauge and associated wiring back to the dash are working properly.

Next, using a voltmeter set to ohms, back probe the Black with Orange stripe wire to ground. If you read less than .2 ohms the ground circuit is good. If not, you’ll need to find the open circuit and or repair the bad ground point.

If both tests indicate the gauge is working properly and the ground point is good, you’ll need to replace the sending unit.

 

Before you go through the hassle of dropping the tank or lifting the bed of the truck to replace the sending unit, suspect the circuit board module (a.k.a "anti slosh module). When facing the front of the guage cluster, there is a plug in module on the upper right hand backside of the cluster. It is a known culprit for causing the gas guage to read inaccurate.

The resister test is a good one to do to rule out the wiring from the sending unit/fuel pump and guage itself.

Only way to change this module is to pull the cluster back enough to pull out the old module and plug in the replacement. Search on this site to locate a step by step procedure with pictures on how to remove the cluster.

My 2000 Ranger fuel guage never read full when I bought it used; I would fill the tank, and the needle would register half a tank. I went to Ebay, bought a refurbished module for 30 bucks shipped (prices range from 25 to about 40 bucks), plugged it in, and fuel guage was perfect after that.

For me, it was either the sending unit in the tank, or this module. The cluster was an easier removal process, so that's why I went that route first. Plus, reading and searching on this fuel guage issue steered me towards the anti slosh module as being the most likely cause.