DrivenJanuary 25, 2011
#367238Tech: 2003-2004 M45 (Y34) Fuel Sending Unit
Disclaimer: This is only a partial fix to a fuel gauge that is incorrectly reading actual fuel level. This will NOT fix any gauge cluster issue you may have.I initially had a perfectly working fuel level gauge, until one day I drove the car rather hard. The fuel gauge then started to read full ALL THE TIME. thinking that the fuel may have sloshed around and got the sender stuck, I decided to take it apart and figure it out. Here's what I found:
Tools:
- common screwdriver
- 8mm socket wrench or normal wrench OR a stubby phillips screwdriver
- two small bags with twist ties
- O-ring for fuel sender unit (~$7)
BEFORE BEGINNING: Work in a well vented area, and make sure you haven't started the engine or turned the key to the On position for at least an hour. this will relieve the fuel pressure.
1. Open trunk
2. Remove carpet, spare wheel cover, and the foam bits surrounding the wheel
3. Remove the push clips that hold the rear trim. There's about 6-8 clips. just pop the centre out towards you, then remove.
4. The top part of the trim is clipped to the trunk. Pull it towards the rear of the car, and the rest of the trim will come out
5. You'll see this:
- Remove the electrical connection
- Grabbing both sides of the fuel line, as indicated by the arrows, pull the fuel line away. WARNING: FUEL MAY SQUIRT OUT... ESPECIALLY if you didn't listen to the "before beginning" bit.
6. Wrap both the fuel line to the engine, and the fuel pump line, in bags using the twist ties to tie them off. This will collect any fuel that leaks out.
7. Remove the six 8mm bolts (8mm socket or phillips screwdriver)
8. Slowly remove the fuel pump/sender assembly. I had to turn it 180 degrees counter-clockwise in order to full remove it. BE VERY GENTLE pulling it out.
9. Here's the fuel pump / sender assembly:
Here is the sender unit components:
In the first picture, the arrow points to a plastic clip that holds the sender unit's arm to the rest of the assembly. This arm is spring-loaded, which is soldered to the lower section in the photo. The picture shows what it would be if the gas tank was empty. Notice the lines behind the arm... the higher the arm goes, the more fuel is in the tank, the higher your gauge should read.
In the second picture, the arrow points to the metal tab that slides on the lines that completes the circuit and ultimately determines where your fuel gauge should read. This metal tab is what is soldered to the spring, and ultimately to the lower section of the first photo. This metal tab is made of some very very thin metal, and is highly prone to being twisted, bent, or otherwise altered from it's normal shape. More on this later...
The third picture shows the arm actually off the unit, only being held on by the wire that makes up the spring and metal tab.
From here, you'll need to do some problem-solving on your own... But, for mine there were two problems:
First, the arm of the sender had popped off, which caused no reading whatsoever.
Second, the metal tab that slides up and down was bent, so when it was reading, it was reading HIGHER than normal... because the metal tab was bent slightly up.
What I did was fixed the metal tab so it was much straighter, without any kinks/bends in it. This allowed for it to read properly.
To test to see if your fuel sender is toast, or to see if what you're doing is making any difference, disconnect the fuel pump from the assembly, by disconnected the electrical connection. This is the black plug near the rubber hose. This will prevent the fuel pump from running without any fuel in it (BAD, as fuel pumps use fuel as a lubricant).
Then, plug the whole assembly back into the chassis harness, turn the ignition to the on position, and adjust the fuel sender unit to go through it's range.
If it still doesn't work, check the wiring on the assembly to make sure there are no broken wires or bad soldering connections. You can also check resistance with a multimeter across the entire range of the sender, but I don't have any details regarding those tests.
So, if you got everything fixed... or unable to fix it, reassembly time!
10. Looking at the gaping hole for the tank, you'll notice a groove around the edge. You should have a gasket there that looks like this:
This will sit perfectly in the groove...
No o-ring
O-ring!
If your old o-ring doesn't fit perfectly, replace it with a new one (About $7). Otherwise, you'll pop a SES (Service Engine Soon) light, explaining there's a small emissions leak :)
11. Replace o-ring!
12. Reinstall fuel sender unit, being very gentle when putting back into tank. You do not want to knock the sender arm off the post...
13. Bolt back down, connect the electrical connection and the fuel line.
14. Start the car to make sure everything is working as it should (hopefully better if you fixed it to start reading fuel levels!).
15. Shut car off and replace the trunk trim.
Viola. Should take 15-30mins from start to finish.
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Disclaimer: This is only a partial fix to a fuel gauge that is incorrectly reading actual fuel level. This will NOT fix any gauge cluster issue you may have. I initially had a perfectly working fuel level gauge, until one day I drove the car rather hard. The fuel gauge then started to read full ALL THE TIME. thinking that the fuel may have sloshed around and got the sender stuck, I decided to take it apart and figure it out. Here's what I found: Tools: - common screwdriver - 8mm socket wrench or normal wrench OR a stubby phillips screwdriver - two small bags with twist ties - O-ring for fuel sender unit (~$7) BEFORE BEGINNING: Work in a well vented area, and make sure you haven't started the engine or turned the key to the On position for at least an hour. this will relieve the fuel pressure. 1. Open trunk 2. Remove carpet, spare wheel cover, and the foam bits surrounding the wheel 3. Remove the push clips that hold the rear trim. There's about 6-8 clips. just pop the centre out towards you, then remove. 4. The top part of the trim is clipped to the trunk. Pull it towards the rear of the car, and the rest of the trim will come out 5. You'll see this: [img]http://thekam.com/images/cars/m45/tech/gastank.jpg[/img] - Remove the electrical connection - Grabbing both sides of the fuel line, as indicated by the arrows, pull the fuel line away. WARNING: FUEL MAY SQUIRT OUT... ESPECIALLY if you didn't listen to the "before beginning" bit. 6. Wrap both the fuel line to the engine, and the fuel pump line, in bags using the twist ties to tie them off. This will collect any fuel that leaks out. 7. Remove the six 8mm bolts (8mm socket or phillips screwdriver) 8. Slowly remove the fuel pump/sender assembly. I had to turn it 180 degrees counter-clockwise in order to full remove it. BE VERY GENTLE pulling it out. 9. Here's the fuel pump / sender assembly: [img]http://thekam.com/images/cars/m45/tech/fuelpump.jpg[/img] Here is the sender unit components: [img]http://thekam.com/images/cars/m45/tech/fuelsender1.jpg[/img] [img]http://thekam.com/images/cars/m45/tech/fuelsender2.jpg[/img] [img]http://thekam.com/images/cars/m45/tech/fuelsender3_off.jpg[/img] In the first picture, the arrow points to a plastic clip that holds the sender unit's arm to the rest of the assembly. This arm is spring-loaded, which is soldered to the lower section in the photo. The picture shows what it would be if the gas tank was empty. Notice the lines behind the arm... the higher the arm goes, the more fuel is in the tank, the higher your gauge should read. In the second picture, the arrow points to the metal tab that slides on the lines that completes the circuit and ultimately determines where your fuel gauge should read. This metal tab is what is soldered to the spring, and ultimately to the lower section of the first photo. This metal tab is made of some very very thin metal, and is highly prone to being twisted, bent, or otherwise altered from it's normal shape. More on this later... The third picture shows the arm actually off the unit, only being held on by the wire that makes up the spring and metal tab. From here, you'll need to do some problem-solving on your own... But, for mine there were two problems: First, the arm of the sender had popped off, which caused no reading whatsoever. Second, the metal tab that slides up and down was bent, so when it was reading, it was reading HIGHER than normal... because the metal tab was bent slightly up. What I did was fixed the metal tab so it was much straighter, without any kinks/bends in it. This allowed for it to read properly. To test to see if your fuel sender is toast, or to see if what you're doing is making any difference, disconnect the fuel pump from the assembly, by disconnected the electrical connection. This is the black plug near the rubber hose. This will prevent the fuel pump from running without any fuel in it (BAD, as fuel pumps use fuel as a lubricant). Then, plug the whole assembly back into the chassis harness, turn the ignition to the on position, and adjust the fuel sender unit to go through it's range. If it still doesn't work, check the wiring on the assembly to make sure there are no broken wires or bad soldering connections. You can also check resistance with a multimeter across the entire range of the sender, but I don't have any details regarding those tests. So, if you got everything fixed... or unable to fix it, reassembly time! 10. Looking at the gaping hole for the tank, you'll notice a groove around the edge. You should have a gasket there that looks like this: [img]http://thekam.com/images/cars/m45/tech/fuelsender_oring.jpg[/img] This will sit perfectly in the groove... [img]http://thekam.com/images/cars/m45/tech/gastank_no_oring.jpg[/img] No o-ring [img]http://thekam.com/images/cars/m45/tech/gastank_oring.jpg[/img] O-ring! If your old o-ring doesn't fit perfectly, replace it with a new one (About $7). Otherwise, you'll pop a SES (Service Engine Soon) light, explaining there's a small emissions leak :) 11. Replace o-ring! 12. Reinstall fuel sender unit, being very gentle when putting back into tank. You do not want to knock the sender arm off the post... 13. Bolt back down, connect the electrical connection and the fuel line. 14. Start the car to make sure everything is working as it should (hopefully better if you fixed it to start reading fuel levels!). 15. Shut car off and replace the trunk trim. Viola. Should take 15-30mins from start to finish.
