fuel guage meter goes crazy on W124
 

Alright, on the 500E, anytime my fuel guage meter shows lower than half full, it starts to jitter and jump. And i'm not talking about like, fluxuating...not gradually changing.

When it hits below half, it will go from half, completely drop to empty, go to 3/4 full, then jump to empty, then back to half.

Something isn't right...anything I can check?

The fuel sending units are a frequent failure item on this chassis. I often read posts that they are still failing on ML's and W210 chassis cars, too.

George Murphy, the technical editor of the Mercedes Benz Club of America, wrote an article about fixing the fuel sending units. The following is quoted from the article:

DISCONNECT THE GROUND CABLE FROM THE BATTERY. A spark around the fuel level
sensor opening could cause a nasty surprise...! (This warning mostly for
gasoline cars, but it is also wise for diesels...)

I have removed several of these units and fixed them - I use a large pair
of channel-lock pliers to unscrew the unit from the tank - they are never
very tight. Access thru the first aid kit opening in the rear window shelf.
Make sure you have less than 1/2 tank of fuel (or less.)

For station wagons, lift the cover out in
the cargo area that covers the recess for the 3rd seat (if you don't have the
third seat.) Gently pull up the "fuzzy" material that lines this recess.
Underneath you'll find the top of the fuel gauge assembly. Carefully remove the
electrical connector. I used a real big Crescent wrench to remove the sender, as
this is something like a 30 or 40mm sized "nut."

Once you get the unit loosened - DON"T PULL IT OUT OF THE TANK TOO FAST! It
will be filled to some level with fuel that will squirt out the the tiny
holes in the bottom. Hold the unit above the fuel level until it is
drained, then using a rag to catch drips, remove it to your work bench.

If it's not all glommed up by algae or other such crud, gently unscrew
the nut on the bottom. Once you remove the tube that surrounds the sender,
(float) you'll find two fine wires running down each side. As you see this
you'll notice the disc on the bottom of the float that contacts the wires on the
points they're soldered to. Check this circuit for continuity when the sender is
touching the contacts. I found that one of the wires on mine was broken. I
carefully soldered it back in place, allowing my little red warning light in the
fuel gauge to work again.

Screw the sender back in place, being careful not to damage the gasket.
Reconnect the electrical connector.


Below from:

Clive Liddell
PMBurg, South Africa
1991 W124 230E (2.3 litre 4cyl)
156kkm
==============================================
Mercedes W123

Test values immersion tube transmitter in ohms
MODEL RESISTANCE: FULL RESISTANCE: RESERVE
Sedan 1.6 ± 0.7 56.9 ± 1.9
T-Sedan 3.2 ± 0.8 52.2 ± 2.1

Testing immersion tube transmitter (removal).
Connect ohmmeter to terminal G (4) and terminal 31 (3) and measure
resistance.
a. In installation position (read out reserve, float below).
b. Rotate by 180° (read out full, float at top).

Testing reserve warning contact.
Connect ohmmeter to terminal W (2) and terminal 31 (3) and measure
resistance.
a. Nominal value 0 ohm in installation position.
b. Nominal value inf. ohm turned by 180°.

Testing harness.
1. Pull coupler from immersion tube transmitter and measure resistance on
jack 3 and vehicle ground. Nominal value 0 ohms (at test value inf. ohm the
grounding line is interrupted).

2. Measure resistance on terminal G (4) and terminal 31 (3) on installed
immersion tube transmitter. Value depends on amount of fuel in the tank.
Plug coupler back on the immersion tube transmitter.

3. Pull coupler from instrument cluster and measure resistance between jack
3 and jack 15.

Nominal value Sedan and Coupe: The value measured under 2. If the value is
attained, the harness is in order (slight deviation caused by length of line
possible).


Nominal value T-Sedan and special vehicles: The value measured under 2
plus 4.7 ohms. If the value is attained the harness is in order (slight
deviation caused by length of line possible)

4. If the measured value is higher or at inf. ohm, the harness couplers (on
instrument cluster, on main harness/tail harness or on immersion tube
transmitter) are having poor contact, a dry joint, or a line is interrupted.

5. If no fault is found during test exchange indicating instrument.

thanks guys :)

anyone have a part # on it? Or exact part name to find it in fastlane?

You are welcome.

Some parts are hard to find or not listed on Fastlane, so I'd either e-mail phil or try the 1-800 number.

I would not suggest a 'pre-emptive' replacement of the sender, since that is what I did, and it made no difference.

My symptoms are very similar to yours, and I now think it is on the gauge end, though I have not yet torn the dash apart to figure it out...

A number of other folks have also reported this problem where it has not been on the sender end, but no clear solution has been presented. I suspect they are all just 'living with it', like myself...

Sender may be a waste of $80, or so...
Better to put an ohmeter on it first to be sure.

ok i took the car to the dealership but they want $250 to do the job. They said its the fuel sender unit, they ran whatever tests they run and came up with that as the solution.

This seems like a job I could do myself though. Heres my main concern, in a W124, 500E, how do you reach the fuel sender? From the pervious post it sounds like you unscrew something from the gas tank through the first aid kit. But in the 500E the first aid kit you'd have to drill through to get to the tank. In the 500E, or W124 in general, is the sender unit near the trunk? If so I have ALOT of audio stuff that needs to be removed to reach it.

Ok...update...I own the W126 cd-manuals because I work on my dads car a lot. So I checked it for where exactly the fuel sender unit is located, and hey what do you know, in the info page they have the W124, W201, and W126 models ;) Sweet. BUT...still a problem....from the diagram it looks like its by the first aid kit...which again is closed off! :(

Anyone know for sure how I can get to it?

http://users.adelphia.net/~nychis/fuelsender.jpg

thats what the cd-manual shows (if i'm copy-write infringementing by posting this picture tell me and i'll edit it off)

If i can get to this i'll take some pictures and post a DIY for it.

awesome, the only thing i can't get the page to load. I'll try again later...if it's down could you e-mail me it? :)

Thanks!

that was an AWESOME DIY, loved it, very detailed

did the new o-ring come with it? Or did you have to get it seperate?

where is everyone finding the fuel sender for $80? The cheapest I could find it was like $110.

By now you have probably figured out it is accessed through the trunk. Once you remove the trim, it is easy to get at.

An easy job. The o-ring is another part.

Best of luck

through the trunk??

ok i'm getting mixed responses here...

I have some people telling me you access it through the cabin by taking the rear seat down
and some people by the trunk??

which is it?

I know you can do it through the trunk, not sure about the cabin and rear seats deal.

I have pulled me ICE enough times to know the tank is right behind that carpet panel in the trunk.

Trunk.