Troubleshooting the fuel sender on a Grand Wagoneer

Contributed By: Chris Medlicott

Symptom: The fuel gauge always reads full with the ignition on and is jammed against the top pin.

Problem: The circuit to the tank sender unit is open due to a wire break, worn sender unit or corrosion.

Neither I nor any member of IFSJA or other person takes any responsibility for any loss of any kind including injury or death as the result of attempted repairs to the fuel sender unit or its associated wiring whether by any negligence on my/our part or otherwise howsoever including any negligent advice given in the following. The following is a record of my successful amateur repair and is written so that others may get an idea of how to fix their own fuel sender. You must make you own assessments of risk of fire and explosion and act accordingly. If you are in any doubt as to your ability (including any law that may prevent you from carrying out fuel system repairs) to safely carry out the following do not attempt it and refer the repair to an authorised repair centre. This document has been written in New Zealand and is governed by the law of New Zealand. By refering to this document you agree to be governed by that law. This document must not be referred to in any jurisdiction where limitation of liability is not allowed to the same extent as the law of New Zealand. Any such repairs made or attempted are entirely at your own risk. Keep a fire extinguisher handy at all times!!!!!

Where to look:

• First tilt the rear seat fully forward and fold back the carpet under the seat.
• Remove the round cover plate just forward of the left rear wheel arch. You may have to drill out the rivets.
• Clean away the accumulated dirt and debris around the fuel sender and hoses.
• Pull off the pink wire and its rubber plug from the center pole of the unit. Take a wire to a known reliable ground and connect it to the pink wire. With the ignition on the gauge should go to zero. If not the break is somewhere in the pink wire and you can start tracing this back without getting into the tank first.
• If the gauge goes to zero when the pink wire is grounded then check the ground from the sender unit. As the tank is plastic the ground needs to be by wire. There is a tab to the side of the sender onto which a black wire connects by way of a black spade connector. This may be corroded with no obvious external damage. (mine was) An easy check is to sand back one of the fuel tubes to shiny metal and take this to a known reliable ground. If the gauge reads correctly with the ignition on and pink wire connected you have found your fault. A simple fix is to solder a wire to a fuel tube (I disclaim all responsibility for any resultant fires. You be the judge whether you do this in situ or not. Safety may dictate removal of the sender unit to do this. I however got away with soldering in situ with a soldering iron) and soldering this in turn to the bodywork. An alternative approach would be to use a clamp eg a hose clamp but this may be prone to corrosion so use of dielectric grease would be indicated.
• If there is still no improvement it is time to delve deeper.
• This is a good time to read that disclaimer again. Think carefully about whether you can do this safely!!!!!
• First clean all around the large nut to remove all traces of dirt. Then make a suitable tool to undo the nut. A piece of mild steel 3/16" x 1 1/2" 8 -10" long is ideal. Bend this in a U so that there is an 85mm gap between the ends. Remove the hoses from the sender (mark these for correct reconnection). Take the tool and carefully unscrew the sender unit nut and remove the sender unit.
• The sender unit can be replaced with a new part or if you are feeling adventurous or poor like me (take your pick!) you can attempt to fix the sender.
• The sender is held together with steel tabs. Carefully bend these back and carefully pull the unit apart. Inside you will see an arm connected to the float arm. Check the end of this for excessive wear. A serviceable repair can be made by soldering a small piece of brass to the end. I cut 1/16" or so off the end of a 3/32 brass bolt, filed it smooth and round and soldered it to the arm to fix the excessive wear.
• Check the state of the ni-chrome resistor wire wrapped around the insulator material. If this is broken you might get away with soldering it or attempting to rewire it (and accept a loss in accuracy). Check the insulator material for straightness. If bent gently pry until it is straight.
• Reassemble. Check that the end of the arm is in contact with the resistor wire throughout its range of travel. You can put it to your ear to check this.
• Check that it now works by connecting the pink wire to the centre pole of the sender unit and earthing it to a known reliable ground and turning on the ignition. Safety may dictate that you first run a long wire from the pink wire and an earth to the sender and to check that the sender does not generate sparks. Fumes from the tank may ignite in the presence of a spark! Make your own safety decisions!

  BE AWARE THAT YOU ARE DEALING WITH FUEL VAPOUR AND ELECTRICITY AND THERE IS CONSIDERABLE POTENTIAL FOR FIRE AND EXPLOSION POSSIBLY CAUSING PROPERTY DAMAGE, SERIOUS INJURY OR DEATH!!!!!!!!

• Turn the ignition off and reassemble making sure the rubber O ring is correctly seated.
• Hopefully everything will now work. Good luck!

©Chris Medlicott, Dunedin, New Zealand. 7 July1998

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