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  #1  
Old 05-14-2019, 11:07 AM
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AWR-fix: Fuel Gauge Sender Repair (fix errant fuel gauge)

Preface: the car ran out of gas with about 4/10 of a tank on the dash. That is waaay to much to be a siphon jet issue. I have a Chinese fuel pump so I actually just assumed that was the problem and bought a new pump before I even looked in the tank.

I was quite surprised when I opened the tank to discover less than 3oz of fuel in the right lobe of the tank. I was even more surprised when I opened the left tank and saw likewise only a couple oz. of fuel!

I dove into hidden menu test 6 and it reported 33L left and 0.0 right.

While I had the senders out I hooked them up and watched the dash and they swept through the full ranges 0-55 and 0-27. I put them back in and did a full tank fill up.

Conveniently just before the gas station entrance is where my car broke down: I did have to use my OTHER X5 to tow it 100' or so into a parking space.

I filmed the fill up live and noticed the left tank stopped climbing at 28L. Right went to 27 as expected.

Even stranger, as I drove away from the gas station, I noticed the left side pop up to 55 as it should.

The dash showed only 3/4 of a tank even when the test 6 was reporting 55+27+82 (full tank) do to averaging. When I reset the fuel system with test 21, it popped right up to 1/1 full tank.

I drove with test six up for much of my driving over the next few weeks to determine what was going on and I saw some erratic behavior on the left sender, namely that it would change value radically. Example, I could tell when the tank was at flood stage where the two sides are just barely flooding over the saddle becuase the right side will settle in at a stable value.

The problem was; that when the left tank had 28L or so it would report at much as 40L.

That's implausible: you can not have more than 29L left unless right is more than 1.5L.

I had a bonus problem that my right sender was only reporting 0.2 vs 1.4L at flood stage, so even with test 6 running it was very scary driving around with only 2/10 of a litter of warning that the left side went dry. Basically I would have to add fuel to keep the right side above flood stage.

Over the next few weeks I saw a few very specific erratic things, specifically that I would see the value jump from 28L to 38L

So I determined without a doubt that the left side sender was sending errant values but always sending something. I could tell based on the flood stage that it was accurate at times.

I couldn't find it but there is a BMW bulletin on repairing the float resistance wiper vs replace the whole sending unit so I set off to do that repair from memory.

Success! Here is what I did:


I put the sending unit in a vice and clamped a quick clamp to stop the float in an exact position.


Measured the Ω value.


Lifted the arm fully


Measured the value. Max reading was 500 Ω. I think that it never gets that high in the tank maybe 450 Ω is full. I'll have to wait until I fill the tank to confirm.


Dropped float arm back to the hard stop


In the exact same position the reading is 20% different! I lifted and dropped a dozen times and it would usually report close to the same value (155) but about 20% of the time some very different value.

Problem confirmed: unreliable resistance sweep.

Now to disassemble:


Unclip the wires.


Release tab on the resistance unit


Remove resistance unit

(Pull off the wire clips. Don't try to unplug the wire just pull the clips off the resistance pads)


Clamp in a vice.


Carefully release the first clip holding the float arm. I used a diagonal cutter to reduce the odds of snapping plastic.
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Old 05-14-2019, 11:09 AM
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AWR-fix: Fuel Gauge Sender Repair (fix errant fuel gauge)


Use a screwdriver to release the second clip holding the float arm.



Remove the arm.


Carefully START to remove the resistance sweeper. Note how it has to lift up on the near side to clear the end stop. Also notice that underneath the actual contacts will get caught so don't force it!


Use the likes of a small screwdriver or awl to lift the contacts to clear the obstruction.


Now continue turning.


And remove the wiper arm.


Bottom view

Now for the fix:


Here's the starting point of the wiper contact springs


I didn't have my contact burnishing tool (don't use sandpaper unless you have 1000+ grit and wet with oil). I used some oiled emery stone but oiled fine knife stone would have been better


Burnishing them using best guess alignment.


After: all roughness removed


Bend the contacts similar to this, it's a bit excessive in that it will cause faster wear but it's made it 18 years it will last a good while with the higher spring pressure.


Clean the contact bars with just some oil and a rag and pressure from thumbnail. Don't use any abrasive they are like 0.0004" thick you could easily wear through.


Reinstall the wiper arm
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Last edited by andrewwynn; 05-14-2019 at 11:39 AM.
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Old 05-14-2019, 11:20 AM
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AWR-fix: Fuel Gauge Sender Repair (fix errant fuel gauge)


Press in the first clip

(Tapatallk wouldn't let me upload that image until I cropped In close, it thought my thumb was private part: if you ever get a random "sorry error" message, and you have flesh colored "stick" in your image do a report error and see if the report says adult image)


Use a thin pliers to press in the other clip. Be careful I'm sure nobody sells just the resistance component


Clip the wires back on! I forgot that step had to do the next step twice.


Push the resistance module back in


Now to test. Note the quick clamp to get repeatable position


165.1 Ω


Maximum position


500 Ω still


Back to the quick clamp stop


Hot dawg! To the decimal same value!



Read 25L before repair, 15L after repair.

Piece of cake*

So one more multiple hundreds of $$ repair for free!

* I always say this after spending months solving a problem.
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Last edited by andrewwynn; 05-14-2019 at 11:58 AM.
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Old 05-14-2019, 02:40 PM
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be happy we can get to both senders

My Z4, the one side is non serviceable, as in you cant replace it, you replace the whole tank

I got a pull last fall and still need to replace that as only 1 sender works, lucky its the fuel pump side so it always reads 1/2 of what actually I have.
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Old 05-14-2019, 09:49 PM
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You could do some clever wiring to convince the car its reading both. Could be as simple as connecting the non working sensor in parallel so you get double the right sender reading.


Sent from my iPhone using Tapatalk Pro
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Old 05-14-2019, 10:42 PM
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true but I was able to get a complete tank and pump for $150 so other than a bunch of labor not bad to have it fixed right
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