[Synchronixity]

Hi, I just bought this car and the gas gauge is reading weird. Before I tear it apart I was looking for any insight.

When the tank is full, it will always read half a tank.

It will then decrease with driving as normal, but does not seem to correlate to being "half scale" (divided by 2) of what is supposed to be there as if a float arm is bent incorrectly.

Additionally when you turn it off and on the reading will go up to a higher reading.

At this point I am usually starting each drive with no gas warning, to triggering the gas light every drive shortly into it, despite not filling the tank at any point between this. Up, down, up, down.

The previous owner mentioned he replaced the fuel pump and then this issue started.

So is it possible he installed the wrong sending unit, or am I looking at more of some type of sensor?

I am a long time mechanic but a BMW newbie so all the sensors and things are new to me.

Thanks
Synchronixity

[Synchronixity]

I have also noticed a slight smell of gas outside of the car sometimes, if it's related. I have yet to smell it inside of the cabin, and no leakage is apparent.

[gbalthrop]

Originally Posted by Synchronixity

Hi, I just bought this car and the gas gauge is reading weird... When the tank is full, it will always read half a tank... Additionally when you turn it off and on the reading will go up to a higher reading...The previous owner mentioned he replaced the fuel pump and then this issue started...

There are TWO (2) Fuel Level Sensors, one on EITHER side of "Saddle-shaped tank". The two sensors are wired to the JBE Module. The Gauge shows the TOTAL of the values from EACH of the 2 sensors. Proper Scan Tool, or Diagnostic Software such as INPA or ISTA will show you, ON Screen, the Value reported by EACH of the two Level Sensors. So you can determine Which Sensor has a bogus value reported, WITHOUT dismantling anything.

Actually, "Hidden Menu 6.00" will display that information on your Instrument Cluster:
https://www.carsaddiction.com/articl...er-hidden-menu

You need a Tool that can "Connect" to the JBE Module to see each Sensor Value, as received by the JBE Module. The fuel pump is on RIGHT side of tank (US Passenger side), and "Jet Pump" pumps fuel from Vehicle LEFT /US driver side of tank to Right Side where Pump is located. So when Fuel Gauge reads 1/4 Tank, Left Side is virtually empty & Right Side is ~ 50% Full.

Prior Owner or Mek-Nik could have messed up wiring or plumbing, but diagnose FIRST & let us know what you find, BEFORE opening tank or ordering parts.
George