240z 1973 tachometer show +- half of real rpm

[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

[Captain_Zeros]

Clarify what you mean "real rpm is on limit"?

A stock 1973 240Z has no electronic rev limiter of any kind, it's all mechanical. On that note, is your Z in stock configuration?

[Reverend]

I think he means that the engine is screaming 10K and then gauge only shows 3K.

[Zed Head]

His resistance numbers imply that he has a Pertronix electronic ignition. When electronic ignition modules start to go bad they can generate electrical noise that the tachometer will see as an RPM signal. He probably hasn't come back because his engine stopped running.