make sure the trunk is unlocked - then just push on the forward end of the cover door and it should tilt open. The trunk lock will also lock the fuel door.
Well on my 1991 Mercedes Benz 190e the fuel release door is automatic. All you have to do is make sure all the doors are unlocked with the master key and then, go to the fuel door and lightly press in on the left side of the fuel door and pull from the right and it should pop open.
On my 91 190e I had that problem once in a bit of a blonde moment. Apparently the gas tank door is linked to the door locks. The doors on the car must be unlocked for the gas tank door to open. I hope your problem is as simple as this.
The fuel door is a hinged door over the fuel-tank filling pipe cavity, and swings outwards, on a vertical axis, to be in open position.
Fuel door is locked when car locked, push on the forward part of door, the aft side will pop out.
My 2006 Mercedes all i have to do is push on the fuel door and it should release and when the car is on lock down it won't open until you unlock the car.
Just push on one side of the fuel door itself (it is not locking).
This model has mechanical linkage in the door so you just have to keep trying to hook the lock rod. It's not really hard but you have to just keep trying.
If Its Like the 1990 model, it doesn't have one. Simply open the car, and press the front end of the gas cover towards the front. That should do it.
if theres not a key hole then its probably a small button in the car otherwise you just pull it open.
open your fuel filler cap door and Mercedes tire pressure recommendations are on a sticker on the fuel door. i personally go 2-4 more psi then recommended.
use a hammer
The fuel door lock is controlled by a vacuum valve (as are the doors locks and many other components on these models). If the car is unlocked, you should be able to open the door easily with you fingers. If the car is unlocked and the door will not open, the valve has failed and needs to be replaced. If you open the trunk of the car and look on the right hand wall of the trunk, you will see a little "door" right behind where the fuel door is. Remove this door and there is a manual release for the door. Hope this helps!