nasty gas fumes in the trunk of a 76 450SL

[speedy72t]

This car is still new to me. Just took it down the road to put some gas in it and the trunk is full of fumes. What's the likely cause? charcoal canister lines? sender unit gasket?

Thanks in advance

When you find out, let me know!

I've discovered that whenever I fill the tank, it reeks of raw gasoline until it reaches about half full (not too long of a wait, or drive, in a 450sl)

I can't see any leaks from the tank, or from the fuel pump back under. And why did they incorporate an elaborate cannister venting system, or is it no longer effective (charcoal) saturated?

[dpatterson]

Speedy I would guess that you have a leak somewhere in the tank venting system. Its supposed to exit via a tube that drops through the floor near the fuel pump. It has a bell shaped end on it and should just dangle next to the pump. Could be its not connected or perhaps blocked at the exit point and therefore venting into the boot ..... er trunk.

Start by having a look under the car at that tube.
To investigate further you need to remove the vertical steel panel that you see when you open the boot. Its got about 30 M6 bolts holding it in - use a 10mm socket on a battery screwdriver (takes hours otherwise with a ratchet) to get these out but chances are the ones along the floor will be corroded as hell. Once you juggle that panel out of the way you will see the venting system on top of the tank.

I'm guessing that the sender gasket is unlikely to be the cause but you can check that quite readily by opening the convertible top cover, lifting the hood up out of the way so that you can see a white plastic bung about 100mm in diameter. Use a flat blade screw driver to pry that up and you will
then be looking straight at the top of the sender unit.

Busybenz -
Why is the venting system there? Think about it .... high pressure flow and return fuel lines for the injection system and gas & liquid that will undergo thermal expansion. Gotta vent it somehow and the 1950's approach of having fuel rise up the filler spout until it over flows isnt exactly ideal.

[Gilly]

If you spilled any fuel when refuelling, there is a small hole in the fuel cap "pocket" area which is supposed to direct any spillage down through a rubber tube and onto the ground. If the tube inside the car is accidentally unattached somehow, or simply falls off, the spillage is directed into the 1/4 panel and trunk area. Seem it before on various models of this vintage.
Gilly

we have had several customers who bring there older SL's in complaining of the same odor, we removed the metal plate between the trunk and fuel tank, opened the cover for the soft top and pulled the two screws attaching the plastic vapor expansion tank, removed it and replaced the hoses, the hoses are part number 107-476-37-26 mercedes sells it by the meter. also while you are in that area replace the o-ring for the fuel level sender unit, it is mercedes number 107-997-13-45

[speedy72t]

Thanks for the advice. I'm so busy I can't see straight till sometime in mid June but I'd really like to get this car driveable. The fuel smell is just one of a long list of things to do before it gets to that point. I've replaced more sender gaskets than I care to think about on 108 cars so that's why I thought of it on this car.

I did replace all the lines associated with the fuel pump and replaced the pressure accumulator while I was under there. I hate gasoline in the armpits so I was tryinig to avoid having to pull that system apart again for the rest of my life. Unfortunately my partner on this project put the tank cover plate back even though we knew there would likely be some problems with those lines. Just have to pull it again.

I seem to remember reading elseware on this board that a clogged charcoal canister can cause minor pressure problems in the fuel injection. Anyone remember wear I might have read that or how to determine wether the cansister needs to be replaced?

Does the part# listed for the vapor lines mimic the original cloth lines or is it a modern replacement? If it's a modern replacement then I'd just assume buy some silicone line and never think about it again.

Thanks for all the help. I've been working with classic MB cars on and off since I was 14 so hopefully I'll be able to return the favor somewhat.

[sublettd]

I'd try replacing the gas cap before resorting to extreme measures. That fixed my problem.

[speedy72t]

I suppose I'll do that too but there's almost no way that all those fumes were coming from a leaky gas cap. This was climb out of car gasping for air amount of fumes.

[sublettd]

Fumes were pretty strong in my car, too.

[Drake]

Not sure but I think yours is the same as my '81 380SL.
I had smell in trunk and inside the car ... took out cover in trunk .. removed vent tank on top of fuel tank and found hole in plastic line from vent tank to where it exits by fuel pump. Thinking it was fixed put it all together OOPS...
disconnected hose from charcol canister and plugged it. Pressurized the line and soaped it end to end . Leak at rigid to check valve hose drivers side by differential ... leak in hose from rigid to charcol canister drivers side by radiator.
No smell at all now !!!!!
Plastic tubing from vent tank to rigid line by fuel pump
2 short hoses from rigid tubing to check valve left side by differencial.
hose under hood from rigid to canister. Good luck AAHHH the smell of fresh air!!

One more thing .... the big fuel line coming down from the bottem of the fuel tank ... looked good but.... the rubber was cracked inside and weeping through to the braid covering ... looked and felt dry but wasn't.
Don't be tricked in thinking 5/8" ID US fuel line works ... tiny bit bigger and puckers the rubber when clamped til not leaking!!!