I'd throw out the schrader valve not opening below a certain psi theory. The should open with very low psi. On the cylinders with zero psi, crank with your finnger over the glow plug holes. You should feel zero pressure, otherwise you had a leak in your compression tester.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked