Somewhere in the system there is a fuel filter in addition to the small sintered bronze one at the fuel distributor. This, on this system, is usually a can looking thing with an inlet and outlet.

They can usually be found under the car along the fuel line somewhere. They were at one time, early on, placed under the hood to make them easy to reach. Then a few of them caught fire when the fuel hoses that connected to them started leaking. So the general design was to move them to under the car.

Think about the early mechanical fuel injection systems Mercedes used. The fuel filter was on the firewall. Easy to reach but a firebomb when the rubber hoses hooked up to it cracked and started leaking.

Go to Pelican's site and search for this fuel filter. Then you will see what it looks like and will know what to look for.