Fuel tank indicator unreliable in the last 1/4

[Coyote_ar]

Hi guys, so im having this problem. I've been measuring my fuel usage, and comparing it with the average mileage given by the OBC. And from 80 to 20 they match spot on.

But when i get to the last quarter ...oh boy. Its completely unreliable, prone to light the reserve light during acceleration, and completely off.
When i filled my last tank, the indicator was almost at the reserve, yet i filled it up and it loaded only 62lts. The time before that, the indicator was at the 20lt mark, and i put in 60lts.

So basically it doesnt matter where im on the last 1/4, i end up loading about 60lts. I cant use that last 20lts in fear of running out of fuel.

Is this normal for the E34? or something is really bad with my fuel tank float/indicator?

[myles]

That's how both of my E34s have been. I put a new sensor in one and it was then only a problem from about 1/8 of a tank, but still a problem. I've read somewhere that the resistance in the wiring connections between the instrument cluster and the fuel sender increase with age and contribute to this problem. I'm not sure if this is the case, but its about the only other thing that I've seen on the topic.

[genphreak]

Never seen it here. Perhaps it's corrosion in a connector?

[632 Regal]

When I replaced the tank on the past E34 it had that problem. The wiring to the float contraption was bad/worn and messing up resistance values when less than 1/4 tank. I ran out of gas due to that, swapped the old pump/float back in and problem solved. PS the original good working one had 270K miles and was still fine. The low mileage one was problematic.

[shogun]

Clean the sender
http://bmwe32.masscom.net/maxf_website/gauge.htm

[Coyote_ar]

ill try that and see if that fixes this readout issue. thx

[Jazz_89]

I have experienced a similar problem. The sensor doesn't seem to have a linear, proportional behaviour. Maybe, the ambient temperature and the tank pressure also contribute to htis issue.