My car's been to MB dealer 4 times now because after filling up and about an hour of driving in heavy traffic the fuel odor is very strong, especially near the fill cap. Here's what they've told me. Anyone else with modded exhaust have similar problem? I would appreciate any input. Thanks.

"From what I’ve boiled this issue down to, I believe the fuel odor is being caused by the temperature in the tank being above normal, which I can only attribute to the aftermarket exhaust. When the vehicle runs for a few hours at idle in the work bay and I also have the heat turned on in the vehicle I can get fuel odor to come out of the vent valve in the charcoal canister. I believe that due to the expanding gasses in the tank, the charcoal canister traps a certain amount of vapors (which it is designed to do) and the purge function cannot keep up with the amount of vapor that’s being pushed into the canister. The purge function is working, however I think that it cannot keep up with the amount of vapor being put into the canister."

" Fuel tank has been replaced twice· Charcoal canister has been replaced twice· Fuel filler neck has been replaced · Vehicle is equipped with aftermarket tune, supercharger pulley, and exhaust.· Aftermarket exhaust has short tube headers and does not have catalytic converters.· Manifold pressure at idle is 280 hPa (absolute pressure) – proper for this engine· Purge function is operating at idle (no spec provided by MB as to when engine control unit activates purge)· Once vehicle is at operating temp, the exhaust below the fuel tank is around 140-150 degrees. The heat shields covering the fuel tank are the same, the parts of the fuel tank that are visible are near 110 degrees. I do not have a like vehicle to compare with. · As vehicle/fuel tank heats up, the amount of expansion is as follows:o 10 min running, shut off valve closed for 5 min: 10hPa gaino 90 min running, shut off valve closed for 5 min: 12hPa gaino 120 min running, shut off valve closed for 5 min: 16hPa gaino 180 min running, shut off valve closed for 5 min: 24hPa gain· Due to this expansion in the fuel tank, I believe the purge function is having a hard time competing with the pressurization (purging works off engine vacuum) allowing the excess vapors to escape the canister."

 

Is it only a fuel smell around the rear of the car, or something you smell in the engine area or inside the vehicle?

 

Once it starts it seems like you smell it everywhere. Doesn't matter windows up or down, air on or off. It's overwhelming. This last time it seemed very strong near the fill cap however.

 

When I had mine replaced the smell was only noticeable after a fill up and the car was in the garage for hours. There was a small amount of fuel pooling if you pulled the rear seats. Honestly, I never noticed the smell but my housemate said he'd get a whiff when the car sat in the garage over night. Zero smell in the car. The smell hasn't come back either.

 

need a new dealer

 

Have you double checked the top of the fuel pumps/sender units for pooling? Some people have had it even after replacement.

I find the exhaust theory difficult. How large is your exhaust, the stock one is already decent size. Is it closer to the fuel tank? If you want to put it to the test, make a thin aluminium heat shield for the top.

 

I have mids, no cats, no resonator, nothing, I even have a flex pipe that might leak a bit right under the driver.

Like I said in the other thread my car smells like fresh air, inside, outside, with the windows down, you name it.

Those dealers are lying to you. You should not be able to smell anything, and it's definitely not because of what they might think it is (modded exhaust affecting pressure in the whatever)

 

Another thing to check is in the engine area. On the fuel rail is a small fuel pressure damper near the rear of the engine. I just replaced one on a customer's 05 SL55. Was dripping fuel in the engine area down the back of the engine and onto the bell housing. Very strong fuel smell in the vehicle.

 

I see you also have Kleeman headers and I assume no such issue like I'm experiencing, right?

 

Thanks, I've asked them to look at the fuel damper.

 

It is odd. The third time I took the car to them they had it for about a month and told me they're having a MB field engineer come look at it. They determined fuel had got absorbed by the seat cushions and replaced them along with new seals and charcoal canister and assured me that was the cause.

This time they've also had it for a month and told me 3 weeks ago that the float valve in the fuel filler neck is sticking and they will be replacing it. I didn't hear hear from them for 3 weeks and when I contacted them I got the reply above. It's hard to believe they have really found the true cause. If my mods or exhaust were causing it there would be hundreds of similar cases and we would all know about it.

 

I believe they have checked the fuel pumps after replacement. My exhaust is whatever is the standard size on these cars I presume, is it 2.5 or 3 inch tubing. Nothing special or different than what other's have done locally.

 

All I know is it's not the exhaust. I feel for you man, somehow these cars manage to have a 2 month downtime a year somehow.

Hopefully bbirdwell will swing by he knows a lot more about the tanks

 

Well, just a quick update. My car's been at MB for over 7 weeks now. They determined it's not the exhaust or mods. I took them another member's E55 with more mods to compare. We ran his car in the shop for almost 2 hours with heat on full blast(that's when mine starts acting up). His exhaust was hotter and slightly higher pressures in the tank compared to mine but no odor or fumes. They have replaced the purge valve and fuel damper, I'm still not sure if that's one component or 2 separate components. They also suspected my ECU was not operating the purge function as it should but I believe we're past that now. They have verified the correct pumps and harnesses have been installed. But the issue still remains.

I believe they're trying their best to resolve this and would appreciate any input or direction from anyone who's experienced this problem or has a suggestion as to what else should be considered.