Strange Fuel Level Issue

[DavidBMW320i]

Hey, So I replaced my left hand side fuel level unit due to the old one leaking fuel when full. The strange thing is when I fill my tank right up it doesnt go to 65Litres. It only shows full at 60Litres when with the old sender unit it went to 65Litres

[Spyke]

Mine did the same exact thing, haven't figure it out yet... For sure it is not the gauges. First things first, double-check your connectors, make sure they are clean and getting good contact.

I'm replacing the pump as well just for kicks, to see if that solves it.

Anyone know why?

Skip to PAGE 3 for the solution to this issue.

[DavidBMW320i]

Yeah it wont be the guages as they were working before I replaced the fuel level unit. The connections are all good. The guage seems to work, just wont show the full 65Litres

[lasmariaspr]

Did you align the fuel level with the tank?

[DavidBMW320i]

Did you align the fuel level with the tank?

Im pretty sure I aligned the top with the line. Ill double check

[fun2drive]

I had to order a new VDO fuel sender for the left side since my sender was leaking as well. I have not put the new unit in place since the part is not in but I did research this and noted something related to correcting an incorrect level. I will research that again to see what it was but since there are two fuel senders one for each side it would seem reasonable they would agree within some spec. If not there must be an adjustment to the sender. I recall that it mentioned a certain ohm rate when up vs down.
I think that might be the deal. I just hope mine doesn't need messed with but who knows.

[DavidBMW320i]

I had to order a new VDO fuel sender for the left side since my sender was leaking as well. I have not put the new unit in place since the part is not in but I did research this and noted something related to correcting an incorrect level. I will research that again to see what it was but since there are two fuel senders one for each side it would seem reasonable they would agree within some spec. If not there must be an adjustment to the sender. I recall that it mentioned a certain ohm rate when up vs down.
I think that might be the deal. I just hope mine doesn't need messed with but who knows.

Interesting. I read in another thread that yes there is a resistance for full and empty in the bentley manual. Very strange since it is a brand new genuine fuel level sensor

[Jdmdro]

swap the pumps like the left to the right and see if it does the same thing and i had a leaky pump to but it ended up being the rubber gasket under the lid

[Spyke]

Found this, and a terrible photo:


Group 62: Instructions
Bulletin Number: 62 12 91 (3421) Woodcliff Lake, NJ
June 1992
Subject:
Fuel Gauge Displays Inaccurate Fuel Tank Level
Models:
3 Series (E36)
Situation:
Two separate, but related complaints may be encountered:

1. The fuel gauge displays an incorrect level; for example, the gauge appears to stick at approximately 1/2.
2. The fuel gauge does not show maximum level when the tank is filled.

Causes:
Two causes may exist for these complaints:

1. Left-hand side fuel level sender (P/N 16 14 1 180 517) sticking (causes gauge to appear to stick at approximately ½).
2. Pump nozzle shuts off prematurely when filling fuel tank, creating the incorrect impression that the fuel tank is full, and the fuel gauge does not show the maximum level.

Correction:
E36 vehicles produced exhibiting complaint "A" as described above should have an improved left-hand side fuel level sender (P/N 16 14 1 180 517) installed. The improved fuel level sender bears a blue date code stamp of "9.91" or later.
Any vehicle exhibiting complaint "A" should be checked for proper alignment of the fuel level senders (refer to sections 16/12-3 and 16/12-4 of the repair manual).
E36 vehicles exhibiting complaint "B" as described above should have the breather line inspected for restriction and position. Refer to Service Information Bulletin 16 01 92 (3553) for this procedure.
Additional Information provided courtesy of ALLDATA



Sounds like the exact problem we are both having. Highlighted in Red. I'm digging some more...

***Can anyone help in finding BMW Technical Service Bulletin 16 01 92 (3553) please? I can't find that one for some reason.

[DavidBMW320i]

Nice Find. Yesterday I checked my Left Sensor Level that I installed recently. I didnt have it lined up 100%. It was about 10mm off centre (about half an inch). I havnt yet filled up my tank to check if this fixes the problem. If it doesnt fix the problem then I guess its the problem as above.

[Spyke]

Nice Find. Yesterday I checked my Left Sensor Level that I installed recently. I didnt have it lined up 100%. It was about 10mm off centre (about half an inch). I havnt yet filled up my tank to check if this fixes the problem. If it doesnt fix the problem then I guess its the problem as above.

Keep us posted David.

[DavidBMW320i]

Ok Spyke. I filled up my tank. Still showed only 60litres instead of 65litres.
I then removed my back seat and covers above the fuel level sensors. According to the Bentley service manual the resistance for both sensors should be 250ohms +- 5 ohms when full. Both sensors should also read the same.

My results
Left sensor (OEM Brand New) 223ohms
Right sensor (intergrated with fuel pump) 250 ohms

The problem is that the left sensor is reading incorrectly. The tank is full as the right sensor is showing full at 250 ohms

I still have my original left sender. I measured the resistance when it was full (all the way up) and empty (all the way down)

My results
Empty 10ohms (Bentley Manual specs 10 ohms +-2ohms)
Full 245ohms (Bentley Manual specs 250 ohms +-5ohms)

This proves that the left sender is reading wrong. My next step would be to remove the sender when the tank is nearly empty and check the resistance manual when its all the way up and all the way down. I also am concerned by that if I keep removing and installing this fuel sender I might break something as its all plastic

My Plan is to measure the resistance when the tank is half full and see if the resistance match the left and right. Then Ill measure it when its near empty

[Spyke]

My Plan is to measure the resistance when the tank is half full and see if the resistance match the left and right. Then Ill measure it when its near empty

Sounds like a good plan. I have my pump still en-route (2 weeks and counting now ), and I will be doing the same. Our identical problems happened after replacing the stock sender, so I'm pretty sure that's going to be the culprit. So for now, this is the only thing that makes sense.

[DavidBMW320i]

Sounds like a good plan. I have my pump still en-route (2 weeks and counting now ), and I will be doing the same. Our identical problems happened after replacing the stock sender, so I'm pretty sure that's going to be the culprit. As I have read, the driver side/sender controls 1/2 to Full readings on the gauges, and the passenger side/pump controls Empty to 1/2 readings. So for now, this is the only thing that makes sense.

Where did you read that the left side control half to full and the right side empty to half ? I believe that, as when I replaced the left fuel sender, the tank looked empty when I had half a tank on my gauge.
Altough in the Bentley Manual it says that if you measure both the fuel senders they should read the same i.e they should be the same fuel level

[Spyke]

It was something I had stumbled upon when I first started trying to narrow the problem down. Since I've read more, it's got to be incorrect. The level is an average taken from both floats/sensors, measured by resistance. (Updated my post so there's no mis-info in this thread.)

Also found this is a somewhat common issue: (See disconnected wire)

[DavidBMW320i]

Yeah that would make more sense being the average. The Bentley manual also says the fuel senders are wired in Series. This would mean if a wire came off like that picture it should show nothing on the gauge.

It would be a good idea to remove the left sender and measure the resistance when its full (all the way to the top) and when its empty (all the way at the bottom).

Also Im wondering if this BMW Part is now a universal part replacement for another model so they just used the same part, in our case its the wrong resistance, as full is 223 ohms

[Spyke]

Right, although a wire getting partial contact may do something different? Not sure on that.

I also had a feeling that one of the part numbers was superceeded by a new part #... you might be onto something there. Wondering if a resistor could be added to compensate if that's the issue.

[fun2drive]

What sender did you buy? I bought VDO from Autohauz because thisis something that you stay with the OEM. My old unit was VDO. I pulled my sender wire harness and the guage read fine which leads me to believe Bentley is wrong and these are in parallel giving you an "average"...

[DavidBMW320i]

I imagine if the wire was partly connected it would make the fuel gauge very erratic when driving, like over bumps etc.

What sender did you buy? I bought VDO from Autohauz because thisis something that you stay with the OEM. My old unit was VDO. I pulled my sender wire harness and the guage read fine which leads me to believe Bentley is wrong and these are in parallel giving you an "average"...

I bought the OEM sender from DDMtuning Part #16141180517. It also has a BMW logo on the top of the sender. Fun2drive do you also have this problem ?

Do you mean you pulled the sensor wire harness from one side and the gauge read fine ?

[Spyke]

What sender did you buy? I bought VDO from Autohauz because thisis something that you stay with the OEM. My old unit was VDO. I pulled my sender wire harness and the guage read fine which leads me to believe Bentley is wrong and these are in parallel giving you an "average"...

VDO all the way, I only do OEM parts for anything other than cosmetics or lighting. If you pulled 1 of the connectors, it should still be fairly accurate, because instead of averaging from 2 inputs, you're getting an average from 1 input. This is of course if you are not driving, sloshing gas from side to side, or parked on a slant.

[DavidBMW320i]

Right, although a wire getting partial contact may do something different? Not sure on that.

I also had a feeling that one of the part numbers was superceeded by a new part #... you might be onto something there. Wondering if a resistor could be added to compensate if that's the issue.

I dont think you can add a resistor to add resistance. The reason is when full my left sender reads 223 ohms. So it needs 27 ohms. But when its down low the low reads 10 ohms. Adding 27 ohms will mess up the low side.

[Spyke]

Thought about that right after I posted... So, since I bought mine from Pelican Parts, I've copied and pasted this whole thread to see if they have an answer. Everything is pointing to the sender being faulty, since it is short-reading the fuel level, and transmitting that bad info to the gauge.

[DavidBMW320i]

Thought about that right after I posted... So, since I bought mine from Pelican Parts, I've copied and pasted this whole thread to see if they have an answer. Everything is pointing to the sender being faulty, since it is short-reading the fuel level, and transmitting that bad info to the gauge.

That would be interesting. I purchased mine from DDMTuning.
The best way to test the sender is if you removed your new left sender unit and measure the resistance when you move it all the way up and all the way down.

It should be 10 ohms on the low and 250 ohms on the high. At least this way you can isolate the sender

And there wouldnt be a USA version or Euro version related problem, as your car is a US version and mine is a Euro version

[Spyke]

*Update: Everything points to the sender feeding the fuel gauge incorrect info. This is due to an incorrect amount of resistance reading at the top swing of the level float/sensor. The correct amount of resistance when the level float/sensor is at it's highest point (full tank) should be 250 (+/- 5) ohms.

Pelican Parts has issued an RMA for me to return the faulty VDO sender. We will see if a new one rectifies the issue. I'll keep this posted with the result.

[DavidBMW320i]

*Update: Everything points to the sender feeding the fuel gauge incorrect info. This is due to an incorrect amount of resistance reading at the top swing of the level float/sensor. The correct amount of resistance when the level float/sensor is at it's highest point (full tank) should be 250 (+/- 5) ohms.

Pelican Parts has issued an RMA for me to return the faulty VDO sender. We will see if a new one rectifies the issue. I'll keep this posted with the result.

Interested to see the outcome. Did you measure your resistance at the high and low point of the suspect sender ? What was the readings ?