Fuel Tank Noise

FLZ_Boy

FLZ_Boy

Regular Member
American Zeds
Joined
Mar 19, 2025
Points
19
Location
Texas
Model of Z
Z3 1.9L
I have this noise like a snorkling sound coming from the fuel tank when I push in the clutch and let off the throttle when changing gears at 6,000+ RPMs. It last about less than a second and it makes me think it's a fuel return problem to the fuel tank.

I have replaced the fuel pump, fuel filter, and fuel regulator and the sound does not change whether the tank is near empty or full.

At this point, in thinking it's the sensor #19 on top of the fuel tank, but I would ask first if anyone had this sound. This is with a M44, 5 Speed Manual.
 
Don't think I have ever changed gears above 6,000 rpm. Is this not the intended fuel cut off to stop the engine over revving?
 
Odd. I dont know what item 19 is as my car doesnt have it and its greyed out in real oem.

The fuel return comes in at the pump housing so its submerged when the tank is full.
 
That part is the fuel tank pressure sensor. Part of the enhanced evaporative diagnostics that was required for the US Federal market and not used where not required - like in the UK.
Issues with that part ‘should’ be detected by the OBD system. Check for evap faults to ensure this system is working correctly.
I’ve never experienced the issue you’re describing, sorry.
 
Ianmc said:
Don't think I have ever changed gears above 6,000 rpm. Is this not the intended fuel cut off to stop the engine over revving?
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Maybe it's a US spec thing, but I have a hard fuel cut off at 6,600 RPMS. I purchased my car that had literally everything original, except an aftermarket turn signal on my mirrors. Doesn't appear if there was any reflashing of the ECU.
 
ChrisD said:
That part is the fuel tank pressure sensor. Part of the enhanced evaporative diagnostics that was required for the US Federal market and not used where not required - like in the UK.
Issues with that part ‘should’ be detected by the OBD system. Check for evap faults to ensure this system is working correctly.
I’ve never experienced the issue you’re describing, sorry.
Click to expand...

I have no fault codes on the car. I have pondered the idea that the last EVAP part I haven't inspected is the EVAP box at the driverside yet. I did change out the fuel breather, but no luck there.

I'll see what happens when I change out the box.
 
To add to the fuel tank sound, it sounds like it's coming from the fuel pump area. The old OEM and new fuel pump makes this noise.
 
My guess would be something in the fuel pressure control system such as the fuel pressure regulator or the 3/2 valve located on the supply line. My guess is that you are suddenly shutting down or pausing a high volume of fuel flowing under high load to the fuel rail, the excess fuel flow continues to flow but is diverted into the tank by the 3/2 (M52) valve for a second causing noise ?
Again, this is a "could be".
View: https://youtu.be/h4C0mmklDiU?si=9KoeRoKEPVcYuL1i
 
I did change the fuel regulator, but not the whole unit (a big white contraption a.k.a 3/2 valve). I probably should replace the entire mechanism instead a piece of it. I do recall the fuel was dirty when I was replacing the fuel filter.
 
Last edited:
Just an update, I replaced the 3/2 valve, but no change in the noise. Sounds like a bearing noise coming from the fuel pump, I thought it was snorkeling at first.
 
Have you had the opportunity to take a look at the pump itself and its associated accessories?
 
Rudyrov said:
Have you had the opportunity to take a look at the pump itself and its associated accessories?
Click to expand...

I looked at the old pump and did replace it with a new one. Nothing stood out unusual.
 
An update, I had an independent shop look at this issue. They determined it was a bad resonator after a series of tests and up the rack inspections. Now to look for a replacement...
 
i took my Z3 to an exhaust shop and they ran a few flow test. They said that the noise could not be coming from the exhaust system. They checked the mounting points and the flow test they peformed said it wasn't problem for my fuel tank noise. Now I'm back to square one.
 
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