I have a 1990 535i that recently developed a hesitation between gears. However, there is a twist. The hesitation worsens when the fuel tank is less than half full. Additionally, the hesitation turns into slow acceleration the lower the tank gets.

My question is this: does anyone have an idea of what this could be.

My only estimate of the problem, is that the fuel filter is clogged or something like that. however, why does the hesitation recede when the tank is full? and if it is not the filter, and is the tank why does it initially just cause hesitation between gears.

I leave it to the gurus to give me an "over the internet" prognosis for the problem.

additionally can anyone tell me where the fuel filter is located on a 90' 535.

Thank you all much