Incorrect Fuel Gage Reading?

[ChiefRider]

So things have been pretty quiet with my E53 lately. Not sure yet if this qualifies as a change.....

I filled the tank 125 miles ago. My 3.0 6MT reliably gets 20 mpg. I noted the fuel gage was at 3/4 full while driving. Reached my destination, parked for 20 minutes, and made 1 more stop 10 miles away, parked for 20 minutes.

On leaving, I noticed my fuel gage was now at 1/4 full, and stayed there, 10 miles home. Turned ignition off and on a few times, gage stayed at 1/4.

Car was locked while parked, so no access to fuel filler. I do not smell any fuel anywhere around the car, and it seems to be running fine.

I will go to fill it up tomorrow to see just what I actually do have in the tank, but in effect I went from 3/4 full to 1/4 after being parked.

Any thoughts?

thanks

[scourtaud23]

I'm going to bet the fuel is still there but you have an issue with your sending units (one or the other). Google "BMW OBD Test No 6" and report the results.

My guess is one of the sending units reports empty.

[andrewwynn]

When below about 1/3 tank the right sender doesn't change. If you got a change of 1/2 tank it has to be the left sender (right side doesn't hold 1/2 tank).

You can measure Ω on the sender unit. (And use test six to confirm).

People have success with cleaning the resistor pad on sending unit to repair a bad sender also occasionally a wire breaks.

You can force the wiper to swipe up and down with some firm g-forces (sharp turns and stop/start).

BMW revised the design of the sending units to have more pressure on the wiper of the resistor so it's a known issue they eventually wont register.


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[ChiefRider]

Thanks guys, with all the snow today, it could be a good day to slosh the fuel around and give the errant sending unit a workout.

[andrewwynn]

Think back to the olde days when a radio would have a scratchy volume knob. You can turn it up and down quick to clean the potentiometer.


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[scourtaud23]

Just so you know, taking out the sender is quite easy and will take less than half an hour.

[andrewwynn]

Especially the left side. No tools for back seat, 10mm socket for 4 nuts, a hammer and punch to turn the big ring. The hardest part is removing the hose clamp. I use finger tight hose clamps when replacing for extreme ease of the next time.


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[scourtaud23]

Originally Posted by andrewwynn

Especially the left side. No tools for back seat, 10mm socket for 4 nuts, a hammer and punch to turn the big ring. The hardest part is removing the hose clamp. I use finger tight hose clamps when replacing for extreme ease of the next time.


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Exactly that and you can replace the punch with a big flathead screwdriver if you don't have one.

[andrewwynn]

Update: I filled up yesterday and measured exactly 82L total. That gives me over 1/1 on the gauge. That only is 21.66 gallons which I've added more than that. I think the official capacity is 92 or something so it is curious why the OBC reports 10 less. I thought maybe was that "zero" was when the light comes on but the light comes on at 8L or 10L in OBC.

[scourtaud23]

The bentley manual says 93L for all with 8L reserve for L6s and 10L for V8s.