Where does a 123 wagon relieve vacuum pressure for the gas tank?
 

I have a 1985 230TE wagon. I was getting a gas smell in the car so I replaced all of the fuel hoses. That part worked great. I no longer have any smell. The issue is I am getting quite a large vacuum created in my tank. Is there a valve somewhere on the 123's to allow air into the tank to prevent this problem. After looking through all my manuals and parts books I can't find this vent. Anyone out there have an idea where this valve may be? I know where the valve is to go to the charcoal canister but not sure where air would be allowed in to equalize tank pressure. Just to let you know how bad it is getting. It is real hard to pull off the gas cap now and I think it has damaged my fuel sender as it no longer functions correctly. I have read of tanks imploding on 123's so I wanted to correct this before it went to far.

Chuck
1985 230TE 5 Speed

I have the 123 diesel, it may be different. But on the right hand side on the top of the subframe, near the subframe mount, is a cone shaped devise that is attaced to a fuel line. The only thing I thought it could be was the vent line for the fuel tank. See if its blocked.

Dave

Here is the 123 wagon fuel tank diagram. Its item number 73 or 73a. This IS for the diesel.

Dave

I pointed out the vents in the diagram.

Dave

PS You have either 73 or 73a. The early/later version.

OK I'm learning here, the picture size format, not the fuel vent system.
I found that using a JPEG format uses a lot of bytes. But that using GIF format allows a large picture and not very many bytes. The 2 picture are 64kb in the first 2 and 42K in the second which is GIF

Dave

Chuck

Are you sure you are getting a vacuum in the tank?

I ask that because my tank is always at a small positive pressure - when I take off the cap at the gas station - pressure escapes.

I am convinced (well 99.9%) that having a pressure in the tank is the normal condition.

I realise we are on different vehicles here 123 v 124 but I would not have though fuel system would be that different.

From my owners manual page 164 Hope this is helpful.

I normally get a little pressure release when I pull up to the gas/diesel station. In both the SL and 300TD. If you llok at the picture, the large one. Item 69 and 79 show the feed and return line. Fuel is sucked into the pumps, One or two. the fuelis used and what is not use is sent back, under a little pressure to the tank. This will slightly pressurize the tank. The item 73 and 73a in the picture is a negative relief valve. Its installed so you don't have the negative pressure that your talking about.

Dave

I suspect that as a grey market vehicle, there has been an evaporative emissions system added.

I'm not exactly sure about an 85 model but many euro models worked like the diesel and vented to the atmosphere. The evap system of the time included a charcoal cannister which recieved vent gases which overcome a roll over low pressure valve (designed to keep fuel in the tank if the car was upside down). The cannister was open to the air at the bottom but the charcoal absorbed the fuel vapors to a point.

During driving a vacuum from the motor was pulled over the charcoal which pulled the fuel vapors into the engine to be burned. Cars of that era had a vacuum operated valve that opened when venturi vac appeared. Unless the cannister becomes sealed there would be no way for intake manifold vacuum to wind up on the tank side unless in was hooked up wrong.

Guys. I have to say that you all have been extremely helpful. After the pictures where posted I went back and looked at my German parts book. The 230TE is supposed to have the cone shapped valve number 73 on your diagram. Now I have to go and check and see if I still have the valve and if it is clogged.

It is definently vacuum not pressure buildup. I know a little pressure buildup is normal in modern closed fuel systems but this is actually vacuum. When I undo the gas cap it is hard to pull off because of the vacuum. I can hear the air been pulled into the tank as I remove the cap. I haven't pulled my fuel gauge sendor out yet but I have a feeling it has been deformed by the pressure and the float is stuck.

As someone stated yes my car was retrofitted with the charcoal canister when brought to the states. Of course there is no way for me to know exactly what was done. I do believe that it isn't hooked up 100% correct though. The canister was hooked to the vacuum line for the vacuum advance. If you look at a 190E 2.3 (same engine). The canister should be hooked to a temperature valve in the head and then routed to somewhere on the intake. I am working on fixing that part as soon as I can find a 190E to look at to get it right. I am going to go take a look and see if I do have this cone shapped pressure valve and see whats up.

Chuck
1985 230TE 5 Speed, BBS, Yokohama, Euro lights just added, 220,000 miles

OK. I wanted to give everyone an update. I jacked up the car to see how it is hooked up. I do not have this valve in the picture. Instead that same line runs to the front of the car to the charcoal canister. I am going to have to figure out what is going on with this thing. I pulled my fuel sender out of the tank and it had imploded. The rod was bent and the case was all distorted. That is how much vacuum was created on a long trip. I have been reading on this forum and others that if there is an issue with the vapor system this can happen. My problem is all my parts are new. I have a new charcoal canister, new check valve, new hoses etc. Any ideas?

Chuck

Well I have good news and bad news. The good news after doing tons of research I found the problem. Thanks to a great Australian web site that completely went over the K-Jetronic fuel injection. I was able to diagnose the problem as a crimped vapor hose. I found the crimps. That is the good news. The bad news is my tank has collapsed from the vacuum. It has a huge "Dent" in the top. Hopefully I can find a used tank somewhere. Along with the fuel level sendor. When the tank colllapsed the sender was pushed into the other side of the tank and was bent and ruined.

Chuck