Gas pump cuts off while fueling my Mercedes C280


#1

I have a '99 C 280, and I am the original owner. I love it except for this one thing. I have always had difficulty pumping gas into it. If I squeeze the handle too fast, or try to set it up for automatic flow the pump cuts off. I found several gas stations which had pumps that didn’t do this, but they have all switched to newer pumps, and now it is difficult and time-consuming to pump the gas. I have to do it pretty slowly, and I can never get it to pump automatically. I have never asked my Mercedes service center about this, because until the past year I was able to find gas pumps that worked OK for me. I would appreciate any help!


#2

There was a requirement for service station pump nozzles to suck the gasoline fumes back during refueling. This may have changed since newer cars are required to have EVAP systems that store their own fumes.
Your car may have a problem with the filler tube; or, it could have an EVAP system problem which isn’t handling the gasoline fumes well enough.


#3

Have you been in the habit of topping off the tank? If so you could be the cause of the problem. Look in the owner’s manual, it likely warns owners about this. In any case, it is likely a problem with the vent/fill mechanism. A clogged charcoal filter, if your car is fit with one. That is the part damaged by topping off the tank, it can also be damaged by other issues. You also could have a crimped hose (there are several hoses there, maybe due to an accident if there has been one.


#4

From what I have learned about evaporative control systems, the vapor pressure in the tank has to build up to a fair amount to exit to the canister. You usually can hear the air/vapor escaping when you remove the gas cap on a warm day. If the filling fuel had to overcome this back pressure, you would get spit back when you removed the filler nozzle. On a lot of cars I have seen a passage that brings air from the top of the tank up to the filler neck that bypasses the fuel going in. The fill station’s vapor recovery system returns this air/vapor mix to the station’s recovery unit. If the air bypass system is blocked, the air has to counter flow to the fuel going in. This will build resistance to the fuel flow and trip the autoshut off. So you might have someone check the patency for that bypass system if your Mercedes C280 has it.

Hope that helps. Let us know if this was the problem on your car.