Jumping Guages

[bbeardb]

My fuel and temperature guage will jump/twitch, sometimes independently of each other and sometime together. The fuel guage will jump less than 1/4 a tank (maybe more like an 1/8). The temp guage about 15 degrees. Do you think this is a problem with the guage, or with the sending units? I'm trying to solve a slight temperature issue, and I'm trying to troubleshoot this, as it might be the cause for my high readings, I don't know.

I actually don't know where my temperature sending unit it, as what I thought it was is probably the grounding switch for my blower fan (see post 42: Name these parts, to help new members.). There is nothing on my valve cover that could be it.

[Diesel Giant]

Temp sending unit should be in the head on the drivers side near the IP pump. Check your ground connections.

[tenknots]

Whack your dashboard when they do that - if it changes, you may have a connection problem on or behind the gauge cluster.

[Hatterasguy]

Sounds like a classic ground problem. I'd remove the grounds and clean them. Maybe even crimp on new ends.

[t walgamuth]

ground

most likely

tom w

[Ken300D]

A poor ground connection is certainly a likelihood, especially if the two gauges jump together like a pair of dancers, at the exact same instant.

On the other hand, you may have two unrelated problems:

1) Fuel level wires dirty on the sensor in the tank.

2) Temperature sending unit going bad.

Ken300D

[jwhughes3]

I've had the exact problem after removing the gauge cluster for speedo repair - going back in and reverifying all connections cured the problem.

John

[SD Blue]

Check your engine-to-chassis ground especially. If loose, it will give the same symptoms.

[andrewtexas123]

What's the best way to clean grounds and fuse connections?

I fixed the jumpy gauge problem on my 240D by adding a separate ground wire from the metal part of the instrument cluster to a ground point under the dash.

[tobybul]

Originally Posted by Craig

I fixed the jumpy gauge problem on my 240D by adding a separate ground wire from the metal part of the instrument cluster to a ground point under the dash.

Thanks, Craig. I guess I was more curious as to what caused the jumpy gages. After looking closely at the ckt board, I found that the ground ckt broke. Its the ckt that goes to pin #15 of the 15-pin connector. #15 is the ground.

Lesson learned: Whenever messing with anything electrical with the car - always disconnect the battery first. I remember way back shorting the terminal going to the clock as I was connecting or disconnecting the cluster. After that, the gages were jumpy. Only now did I notice the ground ckt of the board burned.

The board ckts do not have high ampacity so I can see how this would happen. Obviously less than the smallest fuse so the board ckt acted like a fuse.

So, I am doing the same thing you did - running a separate gound which should accomplish the same thing. I was going to resolder the ckt but its difficult to get to where it broke.

[ImBroke]

Mine was a burnt solder trace on the back of the gauge cluster. How's your cluster look?

[tobybul]

I did run a separate ground wire from the cluster ground to the chassis and that resolved the issue.

The reason the gages got jumpy or bouncy is that they lost their ground. From a suggestion from another member, I closely examined the ckt board where the fuel gage is and traced the problem to an open ground ckt. Mine was on the ground ckt that connects to pin #15.

I wanted to jump it with solder but it was tricky to reach. Running a separate ground does the job.