replaced fuel level sender, needle still jumps - PeachParts Mercedes-Benz Forum

JHZR2 · #1 03-18-2004, 04:18 PM

Hi,

I found that many places have the VDO fuel level sender unit for $60 or so. I purchased one last week, and put it in.

My gauge seems to be just as much off as it ever was. I have gone 290mi, and at startup, the needle sits at halfway on the gauge. OK, thats about right... But then I start driving and it jumps to halfway between 3/4 and 1/2 tank. I dont understand this.

Isnt the fuel sender replacement supposed to cure a jumpy gauge? Thats what I gathered from searching...

Sure seems odd that both would be identically 'defective'.

Is there an easy way to see if the rubber breathing hoses for the tank are clear?

Thanks,

JMH

vahe · #2 03-18-2004, 11:18 PM

I had the very same problem with my 240D, assumed that the sending unit was the problem I asked the mechanic to replace it, he pulled one from another old car and replaced with mine to see what happens, well the needle on the gauge kept acting, he then pulled an old gauge from a dead 240D and replaced with my gage, that took care of it, I had a bad gauge.

Thanks,
Vahe

1977 240D +/-350K

JHZR2 · #3 03-18-2004, 11:25 PM

Is the fuel gauge itself a replacable part, or must I replace that whole portion of the cluster?

Thanks,

JMH

vahe · #4 03-18-2004, 11:34 PM

I believe that the visible portion of the gauge remained in place, the back portion, the electronics were replaced. The entire affair took about an hour to complete.

Thanks,
Vahe

240D 77

JHZR2 · #5 03-29-2004, 12:50 AM

Any reccomendations of a good person who rebuilds these clusters at reasonable rates? Ive noted that a new cluster on fastlane is $318.

Where is a good place to get a replacement? I dont know that I trust used ones from ebay, etc.

Thanks,

JMH

TomJ · #6 03-29-2004, 01:41 AM

You can do the change out yourself.

I just did this same thing with a cluster I pulled at the yard last week. Tested it in my car and the needle jumped all over, sometimes would just go to empty and stay.

You'll have to unbolt the two gauges and unscrew the two screws that hold the oil press gauge to get the back housing off. To get the fuel gauge coil out, you'll have to pull the needle off (not easy), but it's doable at home. Might as well paint the needles while it's out and fix the clock too.

LMK if you just don't want to do it yourself. I'm out of work and looking for anything I can do right now.

Beagle · #7 03-29-2004, 02:20 AM

JMH

Before you spend any money, try this...

A poor earth connection to the instrument cluster casing is a common cause of needles - fuel and temp - jumping randomly on these 123 series. If a sharp thump on top of the cluster causes the needle to jump back then the earth is certainly your problem.

The fix is to pull out the cluster and connect a separate wire from the cluster casing to a good earth point somewhere behind the dash. Two out of my six 123's had this problem.

wolf_walker · #8 03-29-2004, 03:40 AM

Quote:

Originally posted by TomJ
You can do the change out yourself.

I just did this same thing with a cluster I pulled at the yard last week. Tested it in my car and the needle jumped all over, sometimes would just go to empty and stay.

You'll have to unbolt the two gauges and unscrew the two screws that hold the oil press gauge to get the back housing off. To get the fuel gauge coil out, you'll have to pull the needle off (not easy), but it's doable at home. Might as well paint the needles while it's out and fix the clock too.

LMK if you just don't want to do it yourself. I'm out of work and looking for anything I can do right now.

I was going to post almost the exact same thing..

I have given up on relatice accuracy with these fuel gauges, but they should not "jump" around, mild movement up and down with turns is normal though. It's the fact that with a perfectly in spec sending unit, good grounds and as near as I can tell a good gauge, when the reserve light comes on, meaning the float is bottomed out it's range of travel, the most I can put in the car is 16 gallons. I see no evidence of tank disforming, I gave up. I just fill up at 16 gallons-400-500 miles.

The ground idea is a good one, I have an add on ground strap on my cluster, habbit from VDO VW clusters, they do that too.

TomJ · #9 03-29-2004, 11:22 AM

Yes, I should've added that. The ground became a problem a long time ago and I did the jumper to ground thing and even soldered a new ground term to the sender board. Had a burned ground trace on it and had to jumper that.

As many grounds as possible is good. Resolder ALL the conns while it's out.

JHZR2 · #10 03-29-2004, 03:22 PM

Tom: I dont have any experience soldering, etc.
I might just take you up on fixing up my cluster, getting it in shape, re-soldering stuff, adding a few grounds, whatever you've done to yours.

Send me an email regarding what you can/will do, how much you would want, how long you think it would take, etc. My clock is OK, btw.

I was in your shoes not too long ago, but now Im going back to school, so are making a meager stipend, and so have a couple dimes to rub together. Not many, but a couple at least and next to no time. No time + no confidence soldering expensive parts = get someone else to do it.

JMH

JHZR2 · #11 03-29-2004, 09:12 PM

Tom,

If youre on here, check your email, I wrote you a little while ago.

Thanks!

JMH

BoostnBenz · #12 03-30-2004, 04:25 PM

Hopefully I'll have something to add here eventually. My gauge is doing the same thing, so I tried cleaning the sender but it didn't help and I noticed the tabs for the reserve light is gone so I bought a new one, just need to install it now.

FrankM · #13 03-30-2004, 06:09 PM

there are usually complete clusters for sale on ebay. There is a good fuel, temp, oil gauge assembly up for auction right no for cheap money..

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2470463705&category=40017

Stevo · #14 03-30-2004, 08:03 PM

Only one thing I would add to the ground issue. Taking the ground strap off (engine to body, left side) and cleaning the contact area wouldn't hurt. I once forgot to hook it up before starting to wire up the radio, All kinks of strange things happen when the ignition switch is turned on. Anyway I would make sure there is a good connection there. (13mm bolt I think)

Didnt he say that the needle stayed in one place for some time?.. but wouldnt a lose or bad ground make the needle jump? Doesn't seem it would stay still...Or would it

wolf_walker · #15 03-30-2004, 09:27 PM

Quote:

Originally posted by Stevo
Only one thing I would add to the ground issue. Taking the ground strap off (engine to body, left side) and cleaning the contact area wouldn't hurt. I once forgot to hook it up before starting to wire up the radio, All kinks of strange things happen when the ignition switch is turned on. Anyway I would make sure there is a good connection there. (13mm bolt I think)

Didnt he say that the needle stayed in one place for some time?.. but wouldnt a lose or bad ground make the needle jump? Doesn't seem it would stay still...Or would it

The fuel tank needs to be well grounded as well, obviously.

One should pull the sender and the gauge and check the wireing itself per the FSM, it's pretty simple.