parsley

Hi all, Could you please help me with fixing my tachometer issue? I have 240z 1973 us version. The tachometer seams working on the first look properly. But it doesn't because it displays only +- half of real rpm. Tachometer can't go over 3000 rpm but the real rpm is on limit. I checked the coil and resistor and boths are ok. I have red coil 1.5ohm and the resistor is 1.8ohm. Thank you for any suggestions how to fix this issue. Thanks a lot. Kind regards, Radim