Dancing gas gauge fix... MUST READ. - Mercedes-Benz Forum
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post #1 of 11 (permalink) Old 02-29-2008, 11:05 AM Thread Starter
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Dancing gas gauge fix... MUST READ.

So I think I solved the mystery of the 1/2 tank dancing gas gauge dilemma that plagues many Mercedes owners.

Here is what I found.

1. Initially I suspected a bad fuel sender unit so I pulled the sender from the tank and did a ohmmeter and continuity check on it. No problems.

2. It was mentioned before that the cold solder joints on the actual gauge itself may be suspect. I removed the fuel gauge from the instrument cluster and checked that module.

3. After pulling the multi-pin connector from the gauge and reviewing how these fuel gauge mechanisms work I began to suspect that the heater coil component of the fuel gauge might also be heating up the pin connection on socket 3. After 17 years of these heat cycles maybe some oxidation has built up which causes the erratic behavior at higher resistance (ie lower current) values beyond the 1/2 tank mark.

4. I purchased a product from RadioShack called DeoxIt N/ DeoxIt G which is an electrical contact deoxidizer and applied the DeoxIt N to the pins and sockets... soaked them overnight... then applied some horrendously expensive (thankfully there was some @ work) Stabilant 22 (think of it as "aqueous solder") to the pins to improve continuity across the socket/pin bridges.

5. Problem solved. It now appears that enough oxidation was probably built up across the pin/socket to add an appreciable amount of resistance so the gauge was "seeing" that resistance beyond 1/2 tank. Intermittent contact from normal vibrations when driving probably caused the gauge to dance.

So lesson hear is... after ruling out the fuel level sender the next thing to look at is the condition of pin 3 which connects the sender positive to the gauge. Don't underestimate what all those heat/cool cycles can do to the integrity of this pin. Probably explains why the fuel gauge is usually the only thing that goes wonky since it may be the only mechanism that relies on a heating coil to expand and contract the bimetallic strip used for the gauge function (I know that the economy gauge works off vacuum but not sure how the oil pressure or temp gauges work).

Comments welcome.
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post #2 of 11 (permalink) Old 02-29-2008, 11:40 AM
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Good work and thanks for write up! On my 400E I have a similar problem so that's good to know for an easy fix.
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post #3 of 11 (permalink) Old 11-17-2011, 06:02 AM
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bringing this thread up to the top for some clarification.

So, you applied the DeoxIt and Stabilant22 to pins #1 & #3 on both sockets (male and female) in order to cure the issue? Dumb question alert: if oxidation was built up on the pins, couldn't I simply clean the pins with a find sandpaper?

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post #4 of 11 (permalink) Old 11-17-2011, 02:14 PM
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The adjustment on the back of the gage cluster for calibration can also do the same thing with the same fix as first posted. All connections in the system are suspect.
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post #5 of 11 (permalink) Old 11-17-2011, 02:27 PM
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Originally Posted by macdrone View Post
The adjustment on the back of the gage cluster for calibration can also do the same thing with the same fix as first posted. All connections in the system are suspect.
Hmm, that's interesting. I was wondering if I can use that POT to bring the calibration back in line in the "less than 1/2 tank" area of the gauge. Thanks for letting me know that tid bit. I'll play with it tonight.

edit: I tried tweaking the POT to see if the needle would move and it did not. The POT is functioning properly with an approx resistance value of 9 ohm to 149 ohm.

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3.0L/chassis 103.983/ engine 124.030/ DOB 11/1989
1996 FZJ80
2003 4Runner V8
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Last edited by alia176; 11-17-2011 at 05:53 PM.
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post #6 of 11 (permalink) Old 11-17-2011, 08:31 PM
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Now it's funny that someone mentions this.
Recently I removed the back panel to route some speaker wires better than the shop fitters had done and whilst I was there I noticed that my fuel sender wiring was slightly out of the socket. Not much but enough so that you would notice.
I have had a dancing gauge since day 1 and with the price of a sender being what it is, I haven't really concerned myself much about it unless it worsened.

So I pulled the sender plug out completely and gave it a quick puff-blow-shake (technical terminology guys don't try to pretend you know what it is) both ends (wiring and plug in tank) and pushed it back in.

Now it hasn't totally resolved my issuie BUT it doesn't dance as bad as it used to. It's sort of in the quarter tank left department before it does the "Gas Tank Cha Cha". I actually thought nothing much of it (except to remember it), but now someone has pointed the finger at wiring being subject to oxidation I just wonder whether this build up of gunk may also be my problem.

Anyway I will keep an eye on that and if I ever get around to pulling the trunk apart and clean the connectors etc I will report back !

Good Pickup Mate !


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post #7 of 11 (permalink) Old 05-03-2019, 12:49 AM
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i have the same issue.... will follow instructions and return with feedback
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post #8 of 11 (permalink) Old 05-03-2019, 12:52 AM
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i also have a faulty tacho ,any suggestions? this started when i moved a few wires around in the engine bay...
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post #9 of 11 (permalink) Old 05-03-2019, 04:34 AM
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i also have a faulty tacho ,any suggestions? this started when i moved a few wires around in the engine bay...
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post #10 of 11 (permalink) Old 05-03-2019, 07:34 AM
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i also have a faulty tacho ,any suggestions? this started when i moved a few wires around in the engine bay...
Check your fuse connections in the fusebox first.

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