Thanks again.
From: n61cm <jim@tazwade.com>
To: diesel_mercedes@yahoogroups.com
Sent: Sun, January 29, 2012 6:56:41 AM
Subject: [diesel_mercedes] Re: '81 240D wildly fluctuating fuel gauge
Since it started with the new cluster install, perhaps the new cluster is defective. In that case, I'd send it back, wouldn't try to fix it myself. Does the temp gauge fart at the same time as the fuel gauge or at different times? I don't know if they share a common ground but the timing of the problems might tell you something. You can unplug the connection on the fuel sensor and jumper it so it will send full fuel signal to the gauge. Then if the gauge stops jumping, you will know its inside the fuel sender, a common issue on 123s. I guess you could do a similar test with temp gauge wiring as well, though I don't know which way the voltage (or ground) works on that system. It would be odd, though, to have both temp and fuel gauge sensor circuits crap out simultaneously and coincident with the swap-out of the cluster.
Jim
--- In diesel_mercedes@yahoogroups.com, audiolaw@... wrote:
>
> Brian,
>
> The oil pressure gauge is mechanical, I believe, just a tube from the
> engine to the dash binnacle. So no electrical issues.
>
> The symptoms you describe are CLASSIC electrical connection issues.
> Since they appear to affect more than one gauge, the problem is likely to be
> the common ground connection for the binnacle, rather than the individual
> feeds to the gauges. (Although, a fault affecting all the power to the
> gauges MIGHT also explain the symptoms.)
>
> Check the binnacle ground connection. Check not only the wire
> connection, but the base of the pin to which ground connects. The binnacle has a
> printed circuit on the back, and the pin connects to this. Vibration or
> pulling wrong when removing the binnacle might disrupt the pin-printed
> circuit connection. Such a problem might appear only as a tiny crack in the
> circuit trace, and a crack that can be intermittent, thus causing your problem.
>
>
> This is not uncommon in any circuit that is subject to physical
> activity. Examining the circuit traces and connections in VERY GOOD light is
> important.
>
> IF you find a circuit discontinuity, it should be easy to handle with
> a dab of solder. If you don't feel up to that task yourself, you are more
> likely to get quality work at an electronics service shop than at a car
> repair shop.
>
> Tom
>
>
>
> In a message dated 1/28/2012 5:20:47 P.M. Pacific Standard Time,
> brianbarn@... writes:
>
>
>
>
>
> Since recently replacing the instrument cluster in my '81 240D so that I
> would have the amazing luxury of a working odometer, I have a bizarre fuel
> gauge. It flits around quite a bit, and sometimes flies back and forth from
> full to empty and back. Sometimes the movement is less pronounced, say
> from full to 3/4. This movement is not constant - sometimes the gauge is
> just fine. The temp gauge also fluctuates sometimes, but not nearly as much.
> The oil pressure gauge is rock steady all the time.
>
>
> Is this a common situation, and is there a fix? I can estimate fuel usage
> as long as the odometer is working, but it would be nice to have a steady
> fuel gauge.
>
>
> By the way, I got 28.5 mpg on the tank I filled today. Not bad for
> around-town driving.
>
>
> Thanks in advance for the feedback.
>
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