Fuel Gauge issues
 

I recently picked up an E55 and the gas gauge has always read between a full tank and 3/4 of a tank. Never less or accurate.Sometime will read full tank sometimes 3/4... The previous owner told me that after they installed the tank update that the gauge never worked properly afterwards.

So I've been told this could be due to them installing the tank wrong and possible the floats sticking.

Does this sound likely or am i looking at a sending unit replacement? I plan on taking it apart tomorrow. Anything specific i should look for while im in there?


SO UPDATE

I took the tank apart and everything looked okay. Installed the pump and everything back in. Now it will only show between 1/2 and 1/4 of a tank..When i first put it back in it was showing my my fuel light was on and that it needed gas. So went to the pump and put 10 gallons in and it put it right at half a tank. Got out and pumped again until it stopped pumping and when i went back in still showing half a tank??? Any ideas??


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Sounds like the float arm is getting held up by a hose or wire. I'd check the driver side tank float arm (on the filter) first. Be sure to post the fix when your done:)

I know a few techs that work at MB and they all said they think its a float stuck from someone not installing correctly. I'll post pics and info on what i find tomorrow.

Updated

You did verify the sending units for the fuel level on both sides, correct?

No i didn't. How exactly would i go about that? Sorry If that's a stupid question

Not silly at all. You have to open both sides of the tank; both the filter/regulator and the fuel pumps' side. One float is for the driver's side, the other float is for the passenger side of the tank. The fuel pump float is connected via a two-wire connector to the filter/regulator on the driver's side where the signal is routed out of the tank and to the electrical harness. You can see the socket with the blue wires on the fuel pumps in the photo below and you can see the plug in the lower right corner of the shipping box containing the filter/regulator.
https://cimg6.ibsrv.net/gimg/www.mbw...4aa9ccfe70.jpg
https://cimg9.ibsrv.net/gimg/www.mbw...7e176111ee.jpg

Sorry thought you were aware of what Barry posted.It's much easier to work on the fuel tank with minimal fuel in it. You're not going to be able to see much unless you siphon (or pump) out the gas first. It's a little easier to siphon with the car's airmatic fully raised;) It's a stinky and somewhat dangerous job (especially performed in a closed space). Gasoline vapors are quite explosive, please be careful.

Alternatively, pull the panel on the passenger side of the trunk, jumper the fuel pump relay while you have a bleed line attached to the Schraeder valve on the front of the fuel rail in the engine compartment. This post has a pdf showing which two connectors to jumper (pins 30 and 87): https://mbworld.org/forums/w211-amg/...ml#post7284235

FWIW, last time I was lazy and drove my car til I had three bars on the fuel gauge and I still had way too much fuel in the tank when I pulled off the covers. Like pmarino says, drain that tank.

That is brilliant!!:y I'm definitely doing it that way, next time:cool:. Much less fuss and muss, compaired to comming out of the tank port hole:)