pressure build up in gas tank?

[joes]

Hello All,

I hope some one can guide me on this.  I am not that mechanically inclined.  It's a 71 280SL.

Took it out for a spirited drive today.  (2nd drive of the year)  I still have almost a full tank of fuel from when I stored it and it has fuel stabilizer in it.

Started to feel like it was going to stall at idle when stopped after about an hour.  Shaking at idle as well.  It was a pretty hot day at approx 33 degrees C. 

I pulled over and throw in some fuel treatment that I had in the trunk.  I thought it may be clogged injectors and if I drove it a hi revs it might help.  When I open the gas cap fuel shot out of the tank!  About 2-3 cupfuls.  Wow.

I put some treatment in and drove it at hi revs all the ay home.  About 10 mins.  When I got home i shut the engine off and heard what sounded like percolating coffee from the back of the car.  I then opened the cap and a gush of air exhausted from the tank.

The car has always ran like a top.  This never happened before.  Can anyone enlighten me please?

ty in advance.
Joe

[Shvegel]

Big black tank on the left(US SPEC) in the trunk or small blank tank(EURO SPEC) on the right?

[joes]

Thank you for replying.

Car was purchased in Vancouver and always in North America.  I assume US spec.  Fuel cap is on right side above bumper near tail light.  There is also a big spare tire mounted on the right side of the trunk.

[TheEngineer]

vent on gas tank is plugged

[Pawel66]

Thank you for replying.

Car was purchased in Vancouver and always in North America.  I assume US spec.  Fuel cap is on right side above bumper near tail light.  There is also a big spare tire mounted on the right side of the trunk.

Joes, the question was about the fuel expansion tank. You may have it in the back right top corner of the trunk or, a bigger one, on the left hand side of the trunk.

Search "fuel expansion tank" on the forum.

Also: at the bottom outside, next to the rear muffler you should be able to see about an inch tall rubber cone attached to a black vinyl line. Do you have it?

[Peter]

See picture.

[mbzse]

The shape creates a vortex when the car is running.
This helps to extract fumes.
Part No A 111 471 0181

[WRe]

Hi,
if the vent funnel or tank is plugged there should be a vacuum in the tank but no pressure. If it's a US car with US emission  things I would check the vent line to the engine (for gas vapors).
...Wolfgang

[Pawel66]

Well, during a hot day...

[joes]

Good morning and Happy Fathers Day to all.

Thank you for your replies.

I do not see that small rubber cone vent funnel next to the muffler on my car.
Yes I do have the large black fuel expansion tank on the left side.

I have had the car for 10 years and drove it in hot climate before but never experienced this issue before.
I took off the gas cap started it and ran it for 15 mins or so and runs smoothly. 

Is it possible that the gas tank has no vent after all of these years?
Vent line to the engine.  Where is this?

Thank you.

[kampala]

okay.  now we know you have a late usa emissions car.   The blockage is typically in vent lines within the fuel tank or lines going to the expansion tank.

In the trunk, directly on the other side the fuel cap, you will see a metal hump panel next to the spare tire - this panel has a bunch of small screws that hold it in place.  Once removed, you will see two small flexible hoses - they will be connecting the gas tank to the lines that feed to the expansion tank.  I removed these two small flex hoses and ran a thin solid wire into each line - into fuel tank and into lines towards the expansion tank.   

I recall feeling some slight resistance and once pushed through with gentle pushing of the solid wire was able to feed the wire into fuel tank lines and expansion tank lines.   Replaced the small flex hoses and all worked.   No more gasps from the tank.

See tech manual for fuel smell in trunk and you will find the info about the hump panel and small hoses - the access is same.

[WRe]

Hi,
for US fuel venting system see attached documents.
See ja17: https://www.sl113.org/forums/index.php?topic=17082.msg117883#msg117883
Just unplug this fitting on the engine block and see/hear what happens.
...WRe

[mdsalemi]

Ahhh, this brings back old memories.

Some years back this happened to me mostly when the tank dropped below half. I'd get rough running and this "whoosh" when I removed the gas cap.

I cleaned out my vent canister, removed and blew out the hard steel lines in the trunk that go to the vent, the tank, and the FST (funnel shaped thing), and also replaced all the flex lines...while it marginally helped, what really helped me was a new fuel tank.

[joes]

Hi There,

Good info.  I removed the hump near the spare and blew in the tiny plastic lines that go to the expansion tank.  All clear.  I also did the same to the small hard steel lines that are part of the gas tank near the cap.  All clear.

So where is this vent cannister?  What does it look like and how to clean?  Just blow it out?

Sorry for the stupid q.  Thank you

[mdsalemi]

So where is this vent cannister?  What does it look like and how to clean?  Just blow it out?

Right side of your trunk.  Remove stuff in your trunk like the tire, mats, etc. and follow all the lines. There are lines in the very back of the trunk that go from the tank to the canister. The attachment is a screen grab from K&K.

[Mike K]

I had similar issues, see my post with pic from a couple of years ago.
The fuel vent grommet is underneath the car below where the venting tank is.

If you look at the pic in my link, the single line running from the top of the venting tank through the trunk floor, leads to the grommet.
I also replaced this grommet it was blocked with dried mud & dirt etc.

https://www.sl113.org/forums/index.php?topic=27730.msg199616#msg199616