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Volvo fuel gauge sending unit 700

posted by  740man on  Thu Jan 15 16:23 CST 2004
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Hello,

I had the pleasure of fixing the sending unit on my '86 740 GLE
I didn't want to buy a new one as $125.
This is assuming you have the float and lever type sender on some of your cars.
Your tank should be less than half full for these tests. First thing to do is disconnect the sending unit in the trunk and connect a jumper wire between the terminals on the harness connector (green and white?) wires that runs back to the guage. Turn the ingnition on. The needle on the guage should go to full. If you substitute a 68K resistor for the jumper wire (10 cents at raidio shack) the guage should read appx 3/4 full (Haynes). If these tests fail, the fault lies in the guage. (Haynes)
If not it is the sender. Remove the unit. There is a plastic connector on the top metal plate of the sending unit. The wires run through this and into the tank.
If the wires short inside this "cup of hardended goo" well....
I had to cut the wires, drill out the goo, resolder the wires, and fill the now empty cup with silicone and snap it back into the top plate. You can visually inspect and use a multimeter to check all the wire connections once you have the sending unit out.
The unit in my 86 740 is the lever and float type. Easy to check. There is a little metal 'spring tang' thing that runs along a little square resistor plate that sends the tank level signal. Check this over good. Mine somehow was forced past the normal travel and this little tang with the tip that rides on the strip got mangled. Since I didn't have another I had to bend the old one back in shape and make sure it was contacting the resistor strip again. You can then use a multimeter on the Ohms setting and check the values as you move the float arm up and down through it's travels. You can also put one probe right on the strip and the other at the solder connection near the strip and move the probe around on the strip instead of moving the float arm up and down.

APPX. OHMS
Empty 296 ohms
196 ohms
145 ohms
98 ohms
68 ohms
Full 36 ohms

You should be able to find where the problem lies. Recheck all the connections and grounds. This is a good time to refurb the intank pump and screen too.


Hope this helps

740man





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