Fuel level sender - Mercedes-Benz Forum
 
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post #1 of 3 (permalink) Old 12-09-2007, 07:19 PM Thread Starter
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Fuel level sender

I am having trouble with my fuel level gage. On the dash, the needle is burried to the right when ignition key is on. When off, the gage is all the way to the left. I am assuming the gage is working.

At the sending unit I measure just over 8.2VDC on the two wires. One wire goes to the sending unit, the otehr is grounded to the case through a screw. I measured M ohms (almost no connection) accross the two terminals. So, I ordered a new sending unit.

Went to put the sending unit in tonight, and measured the impedance. Still has a few Meg ohms of resistance accross it. I hook up the wires, and the needle is still burried to the right... Do I have another bad sending unit?

My 404 manual doesn't have any schematics or description on the sending units. I am used to 90 ohm variable resistive units (American stuff).

Any help??

-Kyle
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post #2 of 3 (permalink) Old 12-09-2007, 08:21 PM
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troubleshooting 404 fuel level gauge

Kyle,

I think you should be getting more than 8.2V at the sending unit.

As far as I know the power (24V+) to regulate the fuel level gauge in a 404 comes from the hot side of the switch that controls the instrument lights, to the fuel level gauge, through the gauge to the sending unit, to ground. The sending unit acts as a variable resistor.
Check the voltage at the instrument light switch. If you’re not getting 24V check to see if one of the bulbs is partially grounded or remove the line to the gauge and isolate it. Then get 24V some where and by pass the switch right to the fuel level gauge.

You can check the sending unit by putting some additional resistance in series with the sending unit to see if that changes the reading on your gauge. If you don’t have anything else a headlight bulb should make a difference.


Good luck,
Jeff
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post #3 of 3 (permalink) Old 12-10-2007, 07:45 AM Thread Starter
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Do you measure 24V accross your fuel level sender?

If I take the GND and touch it to the other wire, I read empty on the dash. Through chassis GND connection, the gage reads Full. I am in the M ohm impedance which does not seem right to me.

-Kyle
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