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  #1  
Old 07-08-2009, 06:38 PM
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fuel gauge problems

Im having some problems on my old 96 and trying to get a few loose ends fixed before i take it to the new owner. Awhile back the fuel gauge got to the point where it only reads on E no matter how much fuel is in the tank. The sending unit is only a year or maybe 2 old, is it possible that it could fail this quick. how does one trouble shoot and test the sensor?
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  #2  
Old 07-08-2009, 07:59 PM
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Re: fuel gauge problems

luke ill trade ya mine with key off reads full, key on engine off the needle for the fuel gauge and speedo will point at each other. ive heard that means a bad ground somewhere of the sending unit is bad. only place i have found the sending unit locally is at the stealership, prices start at like $250 and go up depending on size of tank.
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Old 07-08-2009, 08:02 PM
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Re: fuel gauge problems

Always on E means the sensor wire to the dash could be shorted to ground.
If you disconnect the sensor wire at the dash and the gauge swings all the way over to past F, then you've got a short in the wire, or the sensor. If it stays on E, new dash or live with it.
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Old 07-08-2009, 08:04 PM
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Re: fuel gauge problems

so since mine stays at full then once key on engine off it swings past full i have a short? sorry for the highjack luke.
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Old 07-08-2009, 09:25 PM
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Re: fuel gauge problems

My fuel gauge (99 truck) has been past F for about a month. I'd like to know why as well. I assumed something had lost connection, but I haven't had time to even research how the gauge works or try to test anything.
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Old 07-08-2009, 09:47 PM
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Re: fuel gauge problems

im doing the wire chasing after finding what wires go to what on the obs, so far have found any breaks for the selector on the frame rail to the gauge. so tomorrow chase more wires.
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Old 07-08-2009, 10:38 PM
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Re: fuel gauge problems

Luke, Rob, Chuckles ,

Here is a few tests and descriptions from the ford manual for the 96:

Fuel Sending Unit

The fuel tank sending unit consists of a variable screened resistor made up of a ceramic substrate. It is controlled by the action of an attached float in the fuel tank. When the fuel level is low, resistance in the fuel tank sending unit is low. When the fuel level is high, the resistance in the fuel tank sending unit is high. As the float moves from empty to full, the resistance will gradually and continuously increase.
The electric fuel delivery system is used on the 4.9L SFI, 5.0L, 5.8L, and 7.5L multiport fuel injection (MFI) engines and utilizes a fuel delivery module (FDM) assembly. The FDM unit includes a high-pressure fuel pump, venturi jet pump, supply check valve, and a shuttle selector valve all located internally in the module, which acts as a reservoir mounted from the fuel tank sending unit flange. The fuel tank sending unit attached to the reservoir body is a separately serviceable component.
In addition, the FDM system achieves a significant reduction in fuel system complexity and simplifies fuel line routing. The in-line fuel filter is located on the left-hand frame rail to provide service access.
The fuel level sensor (9275) for the 7.3L diesel engine operates the same as that described for the MFI engines, except for the following differences:
  • The sender electrical connector has two pins instead of four.
  • The venturi filter screen is replaced by an inverted flexible cone-like member.
  • The flexible cone ensures fuel is always being taken from the bottom of the fuel tank.
  • The cone has as part of its assembly a relief-bypass valve.
  • If the intake becomes obstructed at low temperatures the relief valve opens, allowing fuel to bypass the filter.
The fuel tank sending units used with all engines have a fuel return port that allows excess fuel delivered to the engine to be returned to the fuel tank.

Fuel Level Sensor, Diesel Engine





ItemPart NumberDescription1Fuel Line Assembly (Part of 9275)29275Fuel Level Sensor3Variable Resistor (Part of 9275)4Nipple (Part of 9275)5Float (Part of 9275)6Filter Assembly (Part of 9275)7Surface B (Part of 9275)


Component Tests

CAUTION: During in-vehicle tests, do not let tester terminal studs designated by arrows come in contact with vehicle ground. The gauge will be shorted to the ground, preventing an accurate test and possibly damaging the gauge.
  1. Disconnect connector from the appropriate sender and hook onto the matching terminals on the tester.
  1. Turn the vehicle ignition switch lock cylinder (11582) to ON position.
Fuel Gauge, F-150, F-250, F-350

If only the fuel gauge is inoperative or appears to be out of calibration, a calibration test can be conducted on the vehicle fuel gauge system.
Fuel Tank Sending Unit

With the sending unit float arm in the empty stop position, resistance should be 15 ohms (below E). With the sending unit float arm in the full stop position, resistance should be 160 ohms (above F). The fuel gauge should read empty at 22.5 ohms and full at 145 ohms.
Fuel Tank Second Sending Unit Test, F-Series Dual Tanks

On F-Series aft/axle (standard) fuel tank (9002), the fuel sender electrical connector can be disconnected and attached to a second test sender outside the fuel tank. The float can then be manually operated (up and down) while the fuel gauge operation is observed. Proper gauge function indicates a problem with the fuel tank sending unit located in the fuel tank. Improper operation indicates a problem with the fuel tank gauge or wiring. Refer to Pinpoint Test A in this section.
Fuel Tank Damage
If fuel indicating system components are functioning properly and inaccurate indications continue, check the fuel tank for damage which may have changed the fuel tank sending unit mounting angle and/or damaged the fuel tank sending unit. Make sure the fuel delivery module (FDM) is the correct model for the vehicle and that the FDM is not contacting the bottom of the fuel tank. Also inspect the vent hoses for kinks or obstructions.




Pinpoint Tests


PINPOINT TEST A: FUEL LEVEL READS INACCURATELY


A1 VERIFY POWER AT LOAD SIDE OF FUSE PANEL
  • Key to RUN.
  • Using Rotunda 88 Digital Multimeter 105-00053 or equivalent, verify system voltage at the load side of fuse.
Is the voltage greater than 10 volts?
YesNoGO to A3.GO to A2.
A2 VERIFY POWER AT FEED SIDE OF FUSE PANEL
  • Key to RUN.
  • Using Rotunda 88 Digital Multimeter 105-00053 or equivalent, verify system voltage at the feed side of the fuse.
Is the voltage greater than 10 volts?
YesNoREPLACE the fuse.REPAIR the wiring to the fuse panel.
A3 VERIFY POWER AT INSTRUMENT CLUSTER
  • Have cluster connector(s) remain intact.
  • Partially remove the instrument cluster from the instrument panel.
  • Key to RUN.
  • Using Rotunda 88 Digital Multimeter 105-00053 or equivalent, measure the voltage on the ignition wire at the instrument cluster connector to ground.
Is the voltage greater than 10 volts?
YesNoGO to A4.REPAIR the ignition wire.
A4 VERIFY GROUND CIRCUITRY AT CLUSTER
  • CAUTION: Before checking the continuity of any circuit, make sure there is no voltage present in the circuit prior to switching the test equipment to the resistance function, to avoid damage to equipment. Refer to the test equipment user's manual for additional information.
  • Using Rotunda 88 Digital Multimeter 105-00053 or equivalent, check the continuity of the ground wire at the instrument cluster connector to ground.
Is the resistance less than 1 ohm?
YesNoGO to A5.REPAIR the wire to ground.
A5 CHECK FUEL GAUGE (EMPTY)
  • Key off.
  • Disconnect the fuel gauge sending unit.
  • Connect one lead of the Rotunda Instrument Gauge System Tester 014-R1063 or equivalent to the fuel level sensor input wire at the fuel tank sending unit connector and the other lead to ground.
  • Set the tester to 22 ohms.
  • Key to RUN.
  • Read the fuel gauge.
Does the fuel gauge read E (empty)?
YesNoGO to A9.GO to A6.
A6 RECHECK FUEL GAUGE (EMPTY)
  • Key off.
  • Key to RUN.
  • Tap on the instrument panel.
  • Read the fuel gauge.
Does the fuel gauge read E (empty)?
YesNoF-Series, Bronco, F-Super Duty: REPLACE instrument cluster . F-Super Duty Motorhome: GO to A7.GO to A9.
A7 CHECK PRINTED CIRCUIT BOARD
  • Key off.
  • Disconnect the instrument cluster.
  • Measure the resistance of the circuit between the SIG terminal of the fuel gauge and connector Pins C1-05 and C2-06.
Is the resistance less than 1 ohm?
YesNoGO to A8.REPLACE instrument cluster.
A8 CHECK FUEL GAUGE SENDING UNIT WIRE
  • Key off.
  • Disconnect the instrument cluster and the fuel tank sending unit.
  • Measure the resistance of the Y/W wire (F-Series front) or Y/LB wire (F-Series and Bronco rear) between the instrument cluster and the fuel level sensor.
Is the resistance less than 5 ohms?
YesNoGO to A9.SERVICE the DB/Y wire (F-Series front) or Y/LB (F-Series and Bronco rear) wire between the instrument cluster and the fuel level sensor.
A9 CHECK CHASSIS GROUND
  • Key off.
  • Leave instrument cluster and fuel level sensor disconnected.
  • Measure the resistance of wire to chassis ground.
Is the resistance less than 5 ohms?
YesNoSERVICE short to chassis ground.GO to A10.
A10 CHECK FUEL TANK SENDING UNIT GROUND
  • Key off.
  • Measure the resistance of the BK wire at the fuel level sensor connector to ground at battery.
Is the resistance less than 1 ohm?
YesNoGO to A11.SERVICE the BK wire from the fuel level sensor to ground.
A11 FUEL TANK INSPECTION
  • Inspect fuel tank for distortion or damage.
Is the fuel tank damaged?
YesNoREPLACE fuel tank. REFER to Section 10-01A.GO to A12.
A12 TEST BOX CHECK EMPTY STOP
  • Connect one lead of Rotunda 88 Digital Multimeter 105-00053 or equivalent to the fuel sender signal lead and the other lead to fuel level sensor ground.
  • When the float rod is against the empty stop (closest to fuel filter).
Does the multimeter read 14-18 ohms?
YesNoGO to A13.REPLACE fuel level sensor. REFER to Section 10-01A.
A13 TEST BOX CHECK FULL STOP
  • Connect one lead of Rotunda 88 Digital Multimeter 105-00053 or equivalent to the fuel sender signal lead and the other lead to fuel level sensor ground.
  • When the float rod is against the full stop.
Does the multimeter read 154-162 ohms?
YesNoGO to A14.REPLACE fuel level sensor. REFER to Section 10-01A.
A14 TEST BOX CHECK FLOAT ROD TRAVEL
  • Connect one lead of a Rotunda 88 Digital Multimeter 105-00053 or equivalent, to the fuel sending signal lead and the other lead to fuel level sensor ground.
  • Move float rod slowly from FULL to EMPTY stop position.
Does multimeter reading decrease slowly?
YesNoGO to A15.REPLACE fuel level sensor. REFER to Section 10-01A.
A15 HARNESS CONNECTOR CHECK EMPTY STOP
  • Reattach all fuel indication connectors.
  • Move float rod to empty stop position.
  • Key to RUN.
  • Read fuel gauge.
Does gauge read E (empty)?
YesNoGO to A16.GO to A7.
A16 HARNESS CONNECTOR CHECK FULL STOP
  • Reattach all fuel indication connectors.
  • Move float rod to full stop position.
  • Key to RUN.
  • Read fuel gauge.
Does gauge read F (full)?
YesNoGO to A17.GO to A7.
A17 INSPECT FUEL SENDER
  • Inspect float and float rod.
Is float rod distorted, hitting filter, filled with fuel or loose on float rod?
YesNoREPLACE fuel level sensor. REFER to Section 10-01A.System OK.
PINPOINT TEST B: NO FUEL LEVEL INDICATION, VEHICLES WITH DUAL TANKS (6 PORT FUEL SELECTOR VALVE 7.3L DIESEL)


B1 BYPASS TANK SELECTOR VALVE
  • Disconnect electrical connector from fuel tank selector valve.
  • Key to RUN.
  • Jumper connector terminals No. 4 and No. 5 for rear fuel tank.
  • Fuel gauge should indicate fuel level in rear fuel tank.
  • Move selector switch to front tank.
  • Jumper connector terminals No. 3 and No. 4 for front fuel tank.
  • Fuel gauge should indicate fuel level in front fuel tank.
Does fuel gauge indicate fuel level in front and rear fuel tanks?
YesNoREPLACE fuel tank selector valve. REFER to Section 10-01B.CHECK for faulty fuel gauge, fuel level sensor and/or wiring. REPAIR or REPLACE as necessary.
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Old 07-08-2009, 10:47 PM
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Re: fuel gauge problems

wow is all i gotta say.
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Old 07-08-2009, 10:52 PM
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Re: fuel gauge problems

Quote:
Originally Posted by 3-StarJ.R. View Post
Luke, Rob, Chuckles ,

Here is a few tests and descriptions from the ford manual for the 96:

Fuel Sending Unit

The fuel tank sending unit consists of a variable screened resistor made up of a ceramic substrate. It is controlled by the action of an attached float in the fuel tank. When the fuel level is low, resistance in the fuel tank sending unit is low. When the fuel level is high, the resistance in the fuel tank sending unit is high. As the float moves from empty to full, the resistance will gradually and continuously increase.

...

REPAIR or REPLACE as necessary.
That's what I said, though with many more words.
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Old 07-08-2009, 11:42 PM
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Re: fuel gauge problems

so im gonna go out on a limb and say since mine is way past full its got too much resistance? how do i lower it since i dont want buy a new sending unit since i cant afford one lol
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