E31 fuel gauge issue

[8erBN]

Hey guys need some advise. I have a RHD car 850i (driver on the right side)
Been having fuel gauge issue on the cluster and i did the OBC code test (no. 6 and 7) which stands for “probable fuel left in tank” and “fuel left in tank”


I’ve been getting consistent reading on the LHS and erratic on the RHS. At the moment it sits at roughly 74,0 respectively (refer photo). Tried wiggling the wires didnt work nothing. I realised that I might need to replace the RHS fuel pump w level sending unit.

Question is, is it possible to just buy part number 16141180487 (LHS unit) take the white piece part (sensor) and replace it on my current RHS fuel pump assembly 16147159310?

What wires could possibly be broken on the RHS unit and have you guys encountered similar issues before (if yes, what was the fix)?

Thanks
zie

[Timm]

Although you may well have level-sensor problems the MID test won't help - it reads the sum of both level sensors as they are wired in series. The E38 could read each side separately but the E31 doesn't!

[8erBN]

Although you may well have level-sensor problems the MID test won't help - it reads the sum of both level sensors as they are wired in series. The E38 could read each side separately but the E31 doesn't!

Thanks Timm, whats your advise on the way forward to investigate or fix this?

[Timm]

It is worth saying that if ANY of the fuel-level sensor wires were actually broken then you would get no reading at all - so we can assume everything is connected still. But, most likely the wiper is not successfully making contact with the track. I did this job on the 740i which is wired differently and you can measure each side - at the end of the job I actually repaired the original sender by bending the wiper - all explained here:

https://www.meeknet.co.uk/e38/Sender/Index.htm

....as the sensors are in series you will not know which sender is the problem though without sticking a meter on each one....

[8erBN]

As always, thanks Timm.

Im surprised with how the MID test was designed in the first place now knowing that it is a series circuit. Having reading like 70,0 doesnt help at all in this case and never at all i guess? seems pointless

In the worse case event i have a bad sender on the RHS (often usually expensive), do you think it is possible to just buy part number 16141180487 (LHS unit) take the white piece part (sender sensor) and replace it on my current RHS fuel pump assembly 16147159310?

[Timm]

Take a look at it first - could well be a non-floating float or something just as simple...

[Ldd028]

Hi Timm,


I have an issue on my E31 840ci 1996 RHD where the fuel guage randomly changes e.g from half to full and visa versa. Any thoughts on what could be causing this?

[dragon850]

No, the level sensor is not interchangeable between the sender unit and the pump. Different design.
I would suggest removing and sending it in for a rebuild.

[mostly amazing]

Restarting this thread because I am having issues with my fuel gauge sensor.

I recently purchased and replaced my dual fuel pump unit in the rear passenger side of my 1993 850i due to fuel delivery issues and a dead car. Prior to replacement of the unit, which was purchased from dragon850 (thanks dude), the fuel guage was working fine. After replacement and installation of the new fuel pump unit, my fuel gauge sensor was reading at a half way level, which is correct for the amount of gas that was left in the tank. I refueled the e31 (full tank) but noticed that the level did not increase or read the new fuel amount. The dash reading has since dropped to warning indicator light levels, meaning the tank is empty. However, there is a full tank of gas in the car. My question are:

1. The rear passenger side and driver side units work in tandem, and "chain". What's the best approach to figure out which unit fuel level sensor is failing? Which sensor gives the first reading and which sensor gives the 2nd? Im leaning towards the new unit being the issue, likely with install, since the sensor reading was still set to the prior fuel levels before the passenger side unit was replaced.
2. Would changing the fuel pressure regulators trigger issues with the in tank sensors?

[Timm]

The fuel sensors are in series - one out - both out. The one I would suspect is the one you fiddled with last. The gauge is heavily filtered to sompensate for the fuel sloshing sround which is why you got a reading to start with.

[mostly amazing]

Thanks Timm. I think I will pull out the new unit and make sure the arm with the sensor isn't caught on anything. Is there a position that it should generally be in besides straight down during install?

[Timm]

Check that the wiper is actually touching the resistive arc - that will most likely be the fault