Access to top of fuel tank, 420SEL - PeachParts Mercedes-Benz Forum

William · #1 11-06-2002, 09:21 PM

The car is a 1986, 420 SEL and the gas guage won't stop dancing. I'd like to gain access to the top of the gas tank for removal of the "gas level sender".

From a "search" on the "shopforum", I understood that there is a removable floor panel in the trunk. I couldn't find a floor panel inside the trunk, except for the spare tire, and assume I'm missing part of the instructions.

I would greatly appreciate hearing from anyone who has "been there". Also, any tips on how to correct a "dancing fuel gauge" would be welcome.

Thank you in advance...........William

Q · #2 11-06-2002, 09:48 PM

The fuel level sending unit is accessed from the top of the tank. You have to remove the lower seat cushion to access the bolts that hold the seat back in place. It then slides up and out and you can get to sender. Granted, I don't have the elaborate adjustable rear seat. If you do, it is sure to be a different proposition.

96C220 · #3 11-06-2002, 10:04 PM

Take the bottom of the rear seat out. Look about a foot in from the edge of the seat, at the seam where it meets the floor. You will see a small lever, pull it towards the door of the car, and the seat catch will release. You can then lift out the rear seat bottom.

Carefully remove it and set it aside.

Next, look along the bottom of the rear seat back. You will see three bolts (8mm socket here), with big locknuts on them. One will be on each edge, and will bolt into the side of the car, the third one in in the center of the seat bottom, but may be concealed by a black plastic piece designed to retain tension on the seat belt buckles.

That piece just clips on to the two metal brackets, that extend up to the seat belt buckles. You can easily remove it (you will understand once you take a look at it.

Once the third screw is out. Push the seat up from the bottom. It has to come up around an inch and a half to clear the clips. Once its up, pull it out toward you. You will have to slide the seat belts off the edge of the seat, but after that it will come out easily.

The fuel sender / fuel tank may be accessible there, but I doubt it...

Personally I would go in via the trunk.

When you look at the trunk you will see what looks like a carpeted back wall.

Look closely at where it meets the floor and the rear deck. You may have to pull the floor carpet back slightly, but you will see six 8mm nuts, brass in color. Three across the top, and another three across the bottom.

Remove those, and that back "wall" of the trunk is free to be removed from the car.

This will give you full access to the fuel tank....

That wall is basically designed so you dont have things rolling around and banging into the fuel tank.

As far as the fuel sender - take a VOM meter and measure the ohms it is giving off. It should be steady for any given level of fuel in the tank. You may be able to change the reading slightly by parking the car on an incline, to confirm proper operation.

If its giving a random reading i.e. resistance jumping all over the place then the sender is in fact bad.

Other things that come to mind are possibly a loose ground - does the gas guage dance in motion? Or when the car is stopped as well?

Or possibly a faulty gauge..... This will confirm if the actual sender unit is bad or not.

Hope this helps,

George

Ziad · #4 11-06-2002, 10:13 PM

some 126 chassis (which you have) you can access the sending unit once you have removed the first aid box (plastic compartment next to drivers rear speaker)..if its not clearly visible once you have removed this first aid box....rear seats are next,..the sending unit is hidden by a large rubber grommet at shoulderblade height.

goldstone · #5 11-06-2002, 11:10 PM

About a year ago, the reserve tank warning indicator light on my '89 420SEL's dash stopped working. I've basically just put up with the problem, since on the list of priorities in my life, it has been pretty insignificant. However this thread has caught my attention.

Would fixing my problem be as simple as replacing the sensor on the fuel tank also? (If yes, I would hop right on it.)

Note: The bulb is definitely good (it illuminates every time I crank the ignition.)

Thanks in advance for any insights!

OOPS

I should have done a more careful search before writing. This question has been answered in prior posts regarding MB fuel sender units. SORRY...

William · #6 11-07-2002, 05:33 PM

I greatly appreciate the responses. I don't know what I'd do without your help.

George, as for the questions you asked, up to this point, the fuel gauge dances only when the car is in motion. It is typically erratic when turning corners or hitting bumps.......but sometimes dances during steady driving on a smooth roadway. I have wondered about a loose connection, and I hope that's the cause of the problem. In researching the problem on the "ShopForum", I read where a bad batch of gas can cause deposits on the wires within the "sender"........and careful and delicate cleaning can solve the problem. I'm just not quite sure what solvent to use for the cleaning.

Thanks, William

96C220 · #7 11-07-2002, 11:33 PM

I.e. the wiring in the gas tank....The problem would be constant, and just not when the car is in motion.
Also I think the problem would be of a different nature, moreso the sender reading either constant empty (no output), or being stuck at a fixed reading, regardless of the level of gas in the tank.

Chances are you have a bad ground somewhere. I would check the sender, using the VOM meter....

Now the connection could be loose anywhere between the sender and the gauge, inlcuding the acutal gauge.... To see if the sender is faulty or having the wiring problem, have someone drive the car, while you have the VOM connected to the sender, and see if the reading of resistance jumps around. If the sender output remains steady (with slight variation from incline and gas moving around in the tank) then the problem is on the gauge side. - The gauge could be failing, or have a loose connection at the cluster.

I'm thinking something is loose and causing an intermittent connection, most likely a ground screw that has somehow vibrated its way loose.