Hi everyone. I wanted to share what seems to be a solution to a badly flickering fuel gauge that got worse as the fuel level drops. It was driving me insane. I took out the sender unit in the tank and it was as clean as a whistle. I then saw a video posted by MMWA on Youtube (many of his are excellent) in which he shows the fuel gauge in the dash out of the car and a potentiometer that gets used to calibrate different tanks for the various W124 models. I've known very similar devices getting noisy (e.g. volume controls on amplifiers) so I hooked up 3 wires to the circular plug on the back of the gauges (about 15 pins). One wire is a 12V supply, another (#1) is a Ground and there's a wire for the sender which earths the connection through a variable resistor (effectively the fuel tank sender is a variable resistor).
I just used a single value resistor simulating about 1/4 tank. When I powered it up ---- the gauge flickered just as it does whilst driving! So I then decided to take out the 3 legged potentiometer which is close to the fuel gauge. I used a solder sucker which is NOT the best way of doing it. You can never get every bit of solder out meaning you have to almost lever out the device which in my case succeeded in lifting the solder pad from the PCB. The right way to do it is to used copper desoldering braid as this DOES get it all off.
So I used super glue to stick down the pad and then measured the resistance between each of the two legs of the potentiometer - they were roughly 70 ohms but weren't exactly equal - it will depend on where the calibration point was set. I then used two small fixed value resistors matching the potentiometer values and with plenty of flux (!!!) soldered them in place. The flux makes the solder run beautifully. I also cleaned very carefully the wires of the resistors - cleanliness in soldering is paramount and makes a massive difference.
I then reconnected the 3 wires - and NO FLICKER!!!!
I put the dash back in to the car and still the gauge is steady.
This issue has slowly driven me crazy over the past few years and I know that I'm not alone.
Next, I am going to use the device from "spiyda" to calibrate the tank and gauge accurately (so I'm not bothered that the resistors I used were a few ohms different from my measurements of the potentiometer) and then hopefully we can go on long drives without getting into an argument over the fuel gauge.
Can you imagine what a dealer would have done?? Gone on a parts replacement bonanza I suspect. It cost me a few pennies (and a lot of time over the years I have to admit).
Key message if you attempt this is BUY SOME DESOLDERING BRAID FIRST!
ATB
Neil
I just used a single value resistor simulating about 1/4 tank. When I powered it up ---- the gauge flickered just as it does whilst driving! So I then decided to take out the 3 legged potentiometer which is close to the fuel gauge. I used a solder sucker which is NOT the best way of doing it. You can never get every bit of solder out meaning you have to almost lever out the device which in my case succeeded in lifting the solder pad from the PCB. The right way to do it is to used copper desoldering braid as this DOES get it all off.
So I used super glue to stick down the pad and then measured the resistance between each of the two legs of the potentiometer - they were roughly 70 ohms but weren't exactly equal - it will depend on where the calibration point was set. I then used two small fixed value resistors matching the potentiometer values and with plenty of flux (!!!) soldered them in place. The flux makes the solder run beautifully. I also cleaned very carefully the wires of the resistors - cleanliness in soldering is paramount and makes a massive difference.
I then reconnected the 3 wires - and NO FLICKER!!!!
I put the dash back in to the car and still the gauge is steady.
This issue has slowly driven me crazy over the past few years and I know that I'm not alone.
Next, I am going to use the device from "spiyda" to calibrate the tank and gauge accurately (so I'm not bothered that the resistors I used were a few ohms different from my measurements of the potentiometer) and then hopefully we can go on long drives without getting into an argument over the fuel gauge.
Can you imagine what a dealer would have done?? Gone on a parts replacement bonanza I suspect. It cost me a few pennies (and a lot of time over the years I have to admit).
Key message if you attempt this is BUY SOME DESOLDERING BRAID FIRST!
ATB
Neil
