how to fix the fuel level sender in a w114 - Page 2 - Mercedes-Benz Forum

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post #11 of 25 (permalink) Old 09-18-2013, 09:41 PM
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Have you checked for a resistor by the fuel gauge? That particular circuit may not be working at 12-14V operating voltage.

The three contacts on the sender are ground, reserve light (switch that closes a connection to ground for the light to illuminate) and the float contact, which essentially provides the gauge with a variable resistance in its ground circuit.

The other side (the dash side) of the gauge sees the (switched) positive, and the sender side gets a variable resistance to ground. The reserve light has positive applied to it, and its circuit is completed when the sender level drops and completes the ground.

Hope that helps you figure it out. Not sure how you're going about it, but you might just be in the wrong range to detect the resistance of the wire.

Good luck!
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post #12 of 25 (permalink) Old 09-19-2013, 08:00 AM
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[QUOTE=Palolo;6166457]
The three contacts on the sender are ground, reserve light (switch that closes a connection to ground for the light to illuminate) and the float contact, which essentially provides the gauge with a variable resistance in its ground circuit.

Grounding the sender wires ignition on- one will light up the reserve light. The second one will send the fuel gauge to full and the third is itself ground.

the sending unit resistance wire has a resistance difference of only a few ohms from min to max .forgotten figures now but can check if required .
Adler
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post #13 of 25 (permalink) Old 09-19-2013, 09:06 AM Thread Starter
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Thanks for the info. I got some more resistance wire on the way to try a 2nd time. We will see what happens.
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post #14 of 25 (permalink) Old 09-19-2013, 09:42 PM
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I do hope you have success.it will be a breakthrough in the repair of these very expensive senders .
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post #15 of 25 (permalink) Old 09-19-2013, 10:54 PM
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If you can determine the ohm range that the gauge expects to see, it would be fairly simple to hack the sender to deliver particular ohm readings bck to the gauge for key levels, ie Full, 7/8, 3/4, 5/8, 1/2, 3/8, 1/4, 1/8 or Reserve.

You'd just use bands or strips of copper along the sender, with external resistors, and as the level drops, the needle would move. It would be a stepped motion, not a gradual indication, but it would tell you something...it would "click" from say 3/4 down to 5/8 then stay there until it then clicks down to 1/2, etc.

Not an ideal solution, but something for anoraks who enjoy messing with stuff.

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post #16 of 25 (permalink) Old 09-19-2013, 11:19 PM
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Call me crazy, but couldn't one just go to pick n pull and grab a sender from a newer model gasser and use the wire from that sender? Seems much easier....and heck, you could just pay the cover charge....snip the wire and pocket it....
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post #17 of 25 (permalink) Old 09-19-2013, 11:24 PM
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You're crazy... Where's the fun in that...

Messing about with electrical wires in the fuel tank...
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post #18 of 25 (permalink) Old 09-20-2013, 02:23 AM Thread Starter
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Quote:
Originally Posted by cooljjay View Post
Call me crazy, but couldn't one just go to pick n pull and grab a sender from a newer model gasser and use the wire from that sender? Seems much easier....and heck, you could just pay the cover charge....snip the wire and pocket it....
there are none in the yards here
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post #19 of 25 (permalink) Old 09-21-2013, 03:46 PM Thread Starter
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42 gauge nichrome did the trick. Works perfectly full to empty. Saved $320
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post #20 of 25 (permalink) Old 09-21-2013, 04:34 PM
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Awesome!

Did you take a pic of the repaired sender?
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