System pressure should be about 5bar (70psi + or -). The actual pressure is not as important as that it be steady. If you tee into the supply line and capture the fuel at the return you will be able to test volume at pressure which is the whole test.

Be sure the fuel flows through the frequency valve. Disconnect the electrical and the mixture should go lean. It should be easy to see the results. If pulling the connection doesn't change anything I would investigate.

You might want to verify cam timing also (if you haven't already)

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician