temp/fuel gages bounce, as speed increases - PeachParts Mercedes-Benz Forum

JDmills · #1 07-10-2007, 09:11 PM

I just replaced my dash last week, and have not driven the car much (300TD) until today... and after a couple of miles the tempature gage started to bounce, and ended up pointing to hot (high resistance) The fuel gage did the same, so it seems as if I must have tweeked something?

How is it that the instrument cluster is grounded? May be that is my problem, as even when it is misbehaving, it will flicker to the 'correct' setting about once every time the wheels turn, the faster I go, the more it bounces...

any suggestions? or thoughts as to where to start?

Stevo · #2 07-10-2007, 09:25 PM

In back of the instrument cluster are two grounding nuts with several ground wires to each, check that. All the little screws between the three parts of the cluster transfer the ground so they need too be good and tight. I have attached a new ground to the back of a cluster and that has stopped the "jumps" when all else had failed.

#3 07-10-2007, 09:29 PM

That does sound like a ground problem. The ground is one of the connections on the round connector (brown wire). I had a similar problem on my 240D and solved it by running a separate ground wire from the cluster (metal frame) to the ground point under the dash (bolt with lots of brown wires connected to it).

JDmills · #4 07-10-2007, 10:44 PM

Ok, that makes sense, why didnt I think of that? will have at it tomorow.

Thanks fellas.
Jason

funola · #5 07-11-2007, 12:13 AM

Yeah what they said: ground problems. The fuel and coolant temp gauge share the same ground. If after tightening the grounds behind the cluster and you still have problems, take a look at the 2 related threads below:

http://www.peachparts.com/shopforum/showthread.php?t=189016

http://www.peachparts.com/shopforum/showthread.php?t=189069&highlight=stranded

The problems I had happened over a 2 day period. Everything was fine before that. Basically I had loose and missing starter motor and engine bell housing bolts, which led to a no start, then weird problems with the fuel and coolant temp gauges followed (see post #17 onward in second thread)

plutonian · #6 07-17-2007, 07:35 PM

I probably should'nt be asking questions like this, but how do you access the back of the instrument cluster to check those ground leads!?

plutonian · #7 07-17-2007, 07:42 PM

OK, think I got it here: http://dieselgiant.com/repairyourodometer.htm

JDmills · #8 07-17-2007, 09:41 PM

Hey! I found a nice big short in the ground circut board tracer, er what do you call those lines in the circut board.... anyway, I soddered it to the best of my ability and it fixed the bouncing gage trouble.. Thanks for your help fellas, I am usually leary of electricity, but this was not so bad after all...
jason

#9 07-17-2007, 10:40 PM

Good job.

funola · #10 07-17-2007, 10:45 PM

You found a short or an open? I'd think it's an open, unless you are calling an open a short. Did you take a pic? I wonder if its the same trace that burned on mine which had similar symptoms as yours (jumpy fuel and coolant temp needle). When I take my cluster out next time, I will trace out the circuit and take a pic.

Quote:

Originally Posted by JDmills

Hey! I found a nice big short in the ground circut board tracer, er what do you call those lines in the circut board.... anyway, I soddered it to the best of my ability and it fixed the bouncing gage trouble.. Thanks for your help fellas, I am usually leary of electricity, but this was not so bad after all...
jason

isc62 · #11 07-19-2007, 02:50 PM

it started as a short then it was an open now it's a fixed

vstech · #12 07-19-2007, 02:57 PM

heh, an open short, or a short open? maybe follow the trace and see where it goes and see what would draw current and pop it.

JDmills · #13 07-19-2007, 06:07 PM

you fellas know more about what was going on than I do.... and I just learned what 'open' means.. Thanks for the education

Rashakor · #14 12-13-2007, 10:08 PM

Now,

I have been having the same problem with my gage cluster except that the bouncing only ocurrs when the headlight are on?

I already checked the grounding nuts and the cluster bolts and everything is tight. I am puzzled

JDmills · #15 12-13-2007, 10:53 PM

Bad ground somewhere?? (realize that i dont know much about electricity)...

Or is it the dashboard light circut that is causing the ground problems.. what if you turn your rheostat down until the instrument lights go off, does that change anything???