Article by: Johan
Article applies to: all e32 and e34 models.
Problem: The fuel gauge on my car was erratic in the last 40 liters. The last 20 where the worst. The needle would fall from 20 liters to 0 and go back up to 20 in 2 to 3 seconds. I figured cleaning the fuel sender could cure the problem.
Removing the fuel sender: First get all the junk out of your car’s boot 🙂 Then remove the floor carpet.
Time to remove the access plate:
Clean the uncovered area properly. You don’t want that crud to go into your tank now do you?
Remove the electrical connector:
Some fuel will help you clean the area better 🙂 So get some rags to catch the fuel spillage that’s about to occur.
Remove the fuel lines and keep an eye on them so the right hose comes back to the right fitting.
The second time I took out the sender I first entered a code in the OBC, cranked the engine for about two to three seconds.
This will run the engine but not the fuel pump so the pressure will be off the fuel lines causing less fuel to be spilled.
Remove the nuts holding the top of the sender unit to the tank:
Use some tape or wire to hold the electrical connector and fuel hoses out of the way:
From now on you’ll need both hands. Pull the sender plate upwards and turn it to allow the hoses in the tank to come up:
Allow the fuel to drain from the sender:
Just my luck: the sender is cracked at the bottom. Maybe this happened when the previous owner got the dent into MY fuel tank or maybe someone over tightened the collar nut.
The dent in my fuel tank:
Update: I thought the crack in the level sender and the dent had something to do with the erratic behavior. This was not at all the case.
Cleaning the sender:
After Sean replaced his fuel pumps he had an extra fuel sender…lucky me! When I got it I decided to clean the sender before installing it.
Of course while opening it I broke all the wires. This happened because the pin that guides the float is somehow better attached to the top then the bottom.
Luckily the wiring snapped near the top so I could resolder the wires to the sender.
When I tried to install the sender I noticed it was slightly longer then the one in my car. And you guessed it, it wouldn’t fit.
So I opened my sender as well and you guessed it I broke the wiring AGAIN. In this case somewhere in the middle.
So I soldered the wiring from the 100l sender into my 90l sender. To my surprise this actually worked!!!
To open the sender remove the small nut at the bottom. Be very careful when doing this and make sure the floater guide doesn’t turn along.
When you have the nut off you can carefully pull the plastic cover off.
There are three wires running from the top to the bottom inside the sender. The two thin ones are resistance wires.
These are used by the level float. The float’s guides will short the wiring. By doing this the loop will be smaller thus giving a lower resistance value.
So as the loop gets bigger the resistance values will rise. The proper resistance is between 3.2 Ohm (full) and 88.7 Ohm (empty) for the 90l sender and 3.2 Ohm to 95.7 Ohm for the 100l sender.
The third wire, which is a lot thicker then the other two, will trigger the yellow light which indicates you are running out of petrol.
When the float reaches the bottom of the tank the “empty light” contacts will connect and active the light in the instrument cluster.
I cleaned the wiring with some toilet paper soaked in electrical contact cleaner. As you can see the wiring was quite dirty.
After you reinstall the level sender back into your car your girlfriend will be able to use your car again.
Of course with a working gauge she will run it completely empty giving you a heart attack when you fill up the car and have to pay for the 89.5 liters of fuel (over here at 1.10 euro/liter!!).
Now ask yourself…wasn’t that worth it?
“Oops” update:
I somehow forgot to mention that after the careful dis-assembly, re-soldering and re-assembly of my old fuel sender I well uh…I…uh…I kind of dropped it OK! 🙂
The fuel sender worked OK but the last 20 liters the warning light would go on and off every turn. So when I came across another sender I adopted it and took it home.
The sender which came from a 1991 e32 seems to have an updated design. The outer cover is now a two part piece of plastic where the outer part can easily be clicked off.
And the lower part that broke on my old sender is now reinforced:
