Pressure release noise from fuel tank - 190e

[MarkAndorra]

Hi

When at idle or in drive, I can hear a rhythmic thud or kind of pressure release noise coming from what seems to be inside my fuel tank. It is very rhythmic every 5 seconds or so, and makes no difference if the car is moving or stationary.

I had it down at the local mechanic and he informed me that he has no way to check ass there is no access to the tank.

I also have a slight irregular idle problem once the car is at working temperature. It kind of occilates between 900 and 1100 revs sometimes. It is temperamental. Furthermore, if I don't keep-up a bit of a rev when putting it into reverse, the car can cut out. To start it again, takes quite a few turns of the starter motor again.

When the car is cold it starts first time without any issues.

Had the plugs checked, Idle valve cleaned, relay and fuse checked, and now I am running a quality fuel cleaner through the system to see if that helps.

So, I'm not sure if the weird pressure release type noise in the fuel tank has anything to do with my idle problem, or if they are related.

Any thoughts appreciated.

 

[John77]

Does it do it with the fuel filler cap removed? Obviously not when moving.

 

[mercman111]

has it got a locking cap on

 

[DREAMER NO2]

Pull the cap off and start the car ,,, do you still hear the noise ? And we all have this kind of noise as you open the filler cap , as air surges in to the tank,, its normal

 

[MarkAndorra]

Firstly the car is in very good condition for its age (1987). It has covered 205k km (127k miles).
I only just bought it a few months back and with little use so far. It has been restored to a large degree so I can only assume good wiring and fuel lines.

I have taken off the fuel cap while idling, however the pressure release noise does not change in any way. Neither does this affect the idle.
The sound is similar to a hydraulic valve when releasing pressure, but muted slightly (probably because it is happening inside the tank) and is definitely coming from the fuel tank area. The mechanic said that the fuel pump and filter seem to be fine.

I can only assume some type of back pressure in the fuel system that is accumulating in the tank, then being released. But released where? because there is no obvious sign of air or fuel leaking from anywhere.

I did read somewhere about an additional carbon fuel filter on these cars up near (behind) the front wheel arch, however I do not know if this could be related if indeed this was blocked for example.

Thanks

 

[DREAMER NO2]

MarkAndorra You need a manual for your car . And check out the breather regeneration circuit . The carbon canister is indeed under the front passengers wing you will need to take the plastic inner wheelarch out, to see it, and that circuit is on the same line for the fuel fumes there are valves .But find a diagram if you can to understand how it works.

 

[DREAMER NO2]

Mark this is for the standard W201 Fuel Evaporative System and i have no idea if the cosworth was like this or not . Sorry quality is poor

 

[MarkAndorra]

Thanks for the schematic.
It could be the vent valve, after all it is a valve and subject to pressure one would assume. I'm wondering if this can malfunction and discharge pressure...
Or there is pressure coming more from downstream in the fuel system that is causing a back pressure that manifests itself near the tank area.

I notice that there is a "Siphon Breaker" inside the tank. However, I assume that access to anything physically inside the tank is impossible? Do these tanks come sealed and pre-manufactured parts inside?

 

[MarkAndorra]

The "vent valve" is also known as a breather valve.....

 

[DREAMER NO2]

Mark dont you know any other 190 e owners or even stop asnd ask some one thats got one and ask them if they would remove their fuel caps for you ? i think its the norm my W124 is the same

 

[MarkAndorra]

Will be taking it down to another mechanic in the next week or so, I´ll come back and update.

 

[DREAMER NO2]

Dont see any problem if the car is running well ..