W114 gas smell - Mercedes-Benz Forum

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post #1 of 49 (permalink) Old 08-12-2013, 12:15 PM Thread Starter
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W114 gas smell

Hi,

I have this gas smell around the car and I can't trace the reason for it.
all the lines are replaced and new and see no leaks.
Fuel tank gasket is new.

Checking google gives few other people have the same problem.

One of the suggestions is:
Your car may not have the tank evaporation system, but if it does, the lines are in the trunk behind the spare tire. Check this out and the valve on the system to ensure it is working.


Mine does have the tank evaporation system and visually to me looks clean.
How can I check if its working properly?
Any other suggestions on the gas smell around the car?

Thank you.
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post #2 of 49 (permalink) Old 08-12-2013, 12:50 PM
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My '74 280C does the gas smell thing between 7/8's and 3/4 of a tank. Haven't figured it out yet. I've gone with checking the lines to the expansion tank, checking the diaphragms, changing the cap, replacing the sender gasket and haven't found the cause. Let me know when you find a cure.

I've been thinking about adding a secondary vapor canister where the vent line connects in the front fender well area.

I notice it the most driving with the DS window open so I'm pretty sure it is something to do with the stock vapors tank.

My suspicion is the oxygenated fuel we are getting now. It vaporizes and re-condenses in the vapor canister at a rate greater than the older fuel the cars were designed for and overloads the fume recovery system. This is why I am considering the second canister which hopefully will be enough vacuum load to pull off those fumes. It's worth a try.

Last edited by Mike D; 08-12-2013 at 12:57 PM.
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post #3 of 49 (permalink) Old 08-12-2013, 01:18 PM
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If the valve is clogged, the gas tank will "woosh" when you take off the cap (the pressure will have no where to go but out the filler). On my 108, the fuel vapors are supposed to dump into the crank case to be burned during normal operation. I suspect yours is the same but I'm not as familiar with the 114s as I used to be. I'll see if I can find some info and post it up for you.
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post #4 of 49 (permalink) Old 08-12-2013, 01:28 PM Thread Starter
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Yes, it does whoosh when I open the gas tank cap.
Hmm, it would be interesting to find out how to check the expansion canister.
Thank you.
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post #5 of 49 (permalink) Old 08-12-2013, 02:24 PM
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On the W114C's (and probably the sedans) there is a dual diaphragm set up. It is a pressure relief arrangement. The diaphragms sit at the rear of the car in front of the rear sub-frame/ control arm. The "front" diaphragm gets a low vacuum condition from the suction of the carburetor(s). This lowers the vacuum on the rear diaphragm (the one closest to the tank) and opens a path for any pressure/ fume build up to be pulled through the vent line and burned via the vent line leading to the air cleaner. It's kind of like a constant "burping" but it's only effective when the engine is running.

It's not unusual to have a slight "whoosh" when releasing the cap if the car has been sitting for a while in the sun. If you are getting the "whoosh" immediately after driving the car then you need to check the diaphragms. It won't be a problem with the reservoir tank or it wouldn't be holding pressure.
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post #6 of 49 (permalink) Old 08-12-2013, 02:43 PM Thread Starter
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Ok
Mostly makes sense
Do you have visuals of the diaphragms
How do I check if they are working?
Thank you Mike


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post #7 of 49 (permalink) Old 08-12-2013, 02:45 PM Thread Starter
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Also I run k&n filters instead of factory setup
Will that have an effect?
W114 gas smell-imageuploadedbyag-free1376340329.789527.jpg


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post #8 of 49 (permalink) Old 08-12-2013, 05:02 PM
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I can guarantee the venting system isn't working with that filtration set-up.

Find the vent line and trace it to the carbs. I imagine it is blocked off or left to vent to atmosphere. For the venting system to work it needs a lower than atmosphere condition which is created by the original air cleaner's suction design. When you went to K&N's you removed the low pressure condition which the original system used.

What are you using for a PCV system?
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post #9 of 49 (permalink) Old 08-12-2013, 05:46 PM
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Not sure if it helps, but I uploaded a bunch of stuff for the Zenith carbs. See

http://www.benzworld.org/forums/vint...ml#post5902947

for more info
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post #10 of 49 (permalink) Old 08-12-2013, 06:22 PM Thread Starter
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I use k&n filter
Does anyone have a picture if how this vent line should look like?


W114 gas smell-imageuploadedbyag-free1376353362.557600.jpg




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