STOP:The answers to some of the questions are located in the comments. Also, if you do not see the information you seek in the first post, be sure to use the "Archive Categories" list in the left column or the search bar above.

Saturday, December 20, 2008

1996 Ford F350 Fuel Gauge Reads Full Ar All Times

I have a 1996 Ford F350 Dually and the fuel gauge reads full for both tanks. How do I check this?

1 comment:

Sparky said...

Let's start with the basics and move on from there, have you checked the fuses? Check fuse #17 in the interior fuse block. Make sure the fuse is good and that there is power to it with the key on. Assuming fuse #17 is good you will need to go to the fuel tank selector valve under the truck about middle ways of the driver's side frame rail. You will need to locate the wiring connector that has a yellow w/white, a yellow w/light blue and a dark blue w/yellow wire. There may be other wires in the connector but these are the three you need to access for testing. For testing you will need an ohm meter and if possible you will need two resistors 14-25 ohms and 150-165 ohms or use of a decade resistance box. First disconnect the harness you have previously located and with the ohm meter check the resistance of the yellow w/ light blue wire and a good chassis ground. Record your finding and repeat the test between the dark blue w/yellow wire and a good chassis ground.You will be looking for readings between about 14 to 162 ohms on each test. A reading between these two figures means that your tank sending units are in the okay range. 14 ohms reflects and empty tank and 162 reflects a full tank. If you know about how much fuel you have in each tank, do simple math and figure if it is close. Half tank about 80 to 90 ohms. Quarter tank about 30 to 40 ohms. Three quarter tank 120 to 130 ohms. Here is where resistors or a decade resistance box would be handy, you could simply substitute the values and check the gauge reaction. If have have resistors you will need to connect one at a time between the Yellow w/white wire and a known good chassis ground. Turn the key on and wait about one full minute. 14 to 25 ohms should bring the gauge down to empty and 150 to 165 ohms should bring it to full. If the gauge does not respond accordingly try tapping on the dash at the gauge area. If it starts moving the cluster will need to be serviced. If there is no change you will need to repeat the test at the rear of the instrument cluster on the yellow w/white wire. Now if the tank sending units tested good and you do not have access to resistors or a decade resistance box then you can use a jumper wire connected between the yellow w/white wire and the yellow w/ light blue wire and or the dark blue w/yellow wire. Turn the key on and wait a full minute and see where the gauge moves. If it is close to where you believe the level of the tanks are then the gauge is good and there is a problem in the selector valve itself. The yellow w/light blue is connected to the rear tank and the dark blue w/yellow is connected to the front tank. If for some reason the gauge stays on full when the wires are jumped or when resistors are installed then tap on the dash and observe gauge movement. If the gauge moves after tapping on it then the cluster will need to be repaired.

Hope this helps and please let me know your results,

The Electric Connection