Imploding fuel tank - the sequel (pics included!!) - need another tank

[Dave M]

For the second time in a year, my fuel tank has 'imploded' due to vacuum pressure. I have ~50L capacity remaining, but the sending unit was again smashed to bity bits. I thought, after replacing the last one, that I had solved the problem. I made sure all the hoses were clear and swapped the filler cap. Oh well, better luck next time.

Anyhow, two questions:

1) How is the system kept at a reasonable pressure? Is it the filler cap or something else?

2) Anyone have a line on a good tank or sending unit? I would need it shipped to 55605.

Thanks for reading,

Dave

http://img.photobucket.com/albums/v11/dave_macisaac/May_7_2015%20065_zpscel2o4in.jpg (http://smg.photobucket.com/user/dave_macisaac/media/May_7_2015%20065_zpscel2o4in.jpg.html)

http://img.photobucket.com/albums/v11/dave_macisaac/May_7_2015%20066_zps1lm7eilj.jpg (http://smg.photobucket.com/user/dave_macisaac/media/May_7_2015%20066_zps1lm7eilj.jpg.html)

[shogun]

There is a breather valve in the engine bay http://2009.bmwfans.info/parts/catalog/E34/Sedan/USA/535i-M30/LHD/A/1992/june/browse/fuel_preparation_system/fuel_tank_breath_valve_disturb_air_valve/
close to the charcoal filter.
For a quick test: the air breather valve should have a resistance of 45 ± 20 Ohm, without power it is closed.
Also check the drain pipe of the charcoal filter. When engine is running, the active carbon filter should be flushed with air automatically, this will re-renerate the active carbon filter and the fuel mist is led into the intake system of the engine.
There is also an expansion tank, on my E32 in the wheel housing of the right rear wheel, you have to remove the mud cover to see all the hoses. http://2009.bmwfans.info/parts/catalog/E34/Sedan/USA/535i-M30/LHD/A/1992/june/browse/fuel_supply/

The filler cap has no hole anymore for emission reasons, that was in the past. Some people however drill a small hole into the cap, but then on U.S. models you will probably get a CEL for large evap leaks, at least that is the case on my U.S. spec E36 M3, when my wife forgets to close the gas cap correctly.

[Dave M]

Aha, thanks again Shogun. I recall the hoses from the expansion tank but didn't know they eventually connected to the canister/breather valve. I think you're on the right rack.

Dave

[632 Regal]

I agree with Shogun, somethings wrong and I will guess right in front of your eyes. Please post as you go along.

[Bill R.]

The gas cap should have a one way check valve which allows air in but not out. This way the tank can suck air in as the fuel level goes down to keep from creating a vacuum. The Solenoid valve in the engine comparment opens up when the engine is running to draw vapors from the charcoal canister and the expansion tank. The manifold vacum when the solenoid valve is open and the engine is running is great enough combined with the electric fuel pump sucking also is great to enough to cause the tank to implode if the gas cap one way vent isn't working...

[shogun]

Thanks. According to this info the pressure/vacuum relief valve is only on older pre OBDII vehicles, article: evaporative emission control system http://www.aa1car.com/library/evap_system.htm
So my 11/1988 32 should have such a valve, the 1998 E36 M3 should not have it.

[Dave M]

So I should try another gas cap first?

[632 Regal]

So I should try another gas cap first?

What car is this for? Reread and didnt see anything but this:


So my 11/1988 32 should have such a valve, the 1998 E36 M3 should not have it.

[Dave M]

10/90 Build 525 (M50)

[632 Regal]

I would try the gas cap first.

[Dave M]

I would try the gas cap first.


Will do

[632 Regal]

Will do

You know, why don't you check the part number on your cap and cross it with realoem?

Another option is to suck on the cap and see if it draws in air. Bad picture...

Get a vented cap, whatever the situation a vented cap will prevent it.

Case closed.

Report back soon.