You admit the car is used?
You have not replaced the fuel filters.
You do not know what the PO was running for fuel.
You have no idea of fuel filter age.

You are going to start diagnosis at the fuel tank screen?

Why?

Suggest you install a new secondary filter, before you take a bath in fuel.

I have a neighbor, eight blocks away, 1983 300D, he runs 70% used motor oil with 30% used hydraulic oil to thin it down, all free from the plant where works, his filters plug up every 2 - 3 months.

If you don't know what the PO ran for fuel, change the secondary filter, then you have a base line to start from.

__________________
ASE Master Mechanic

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D

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