Tach bounces & doesnt go past 4.5k after Pertronix install

[boro92]

I just installed the Pertronix Ignitor with their 3.0 ohm coil and bypassed the ballast resistor.

The car actually runs very well after a timing adjustment. However, I noticed that the tach doesnt rev past 4.5k under hard acceleration.

Any idea what would cause this and what can remedy the situation? The tach operated fine when I was using the original points and ballast. No bouncing, no nothing...just reliable. Now it's all funny! Is something going wrong in the electric circuit?

[beermanpete]

The early 240Z uses a current-pulse driven tachometer (typically referred to as a 4-wire tach). The current pulse from the Pertronix ignition is likely different than with points. This could cause problems with tach operation. You might need to use an aftermarket tach or get one from a 280Z with the voltage driven (3-wire) input.

[Arne]

If connected correctly, the early 4-wire tach works perfectly with the pertronix set up. I ran mine w/o issue.

We need to clarify - is the issue just that the tach does follow the engine revs? Or does the engine not rev past 4500? Completely different set of things to look at.

[boro92]

If connected correctly, the early 4-wire tach works perfectly with the pertronix set up. I ran mine w/o issue.

We need to clarify - is the issue just that the tach does follow the engine revs? Or does the engine not rev past 4500? Completely different set of things to look at.

Hey Arne,

Thanks again for the help on this matter!

The tach doesnt go past 4.5K under hard accelleration, but the engine continues to pull and revs will continue to climb as expected.

Not sure what's causing the tach to go all funny.

[Unkle]

You have the Canadian metric tachometer , and the Petronix is in US Imperial rpms .

BWAHAHAHA...........

sorry . : )

[beermanpete]

It seems your tach is bad. Arne has verified the Pertronix is not the cause and you say the car is running fine. The only thing left is the tach itself. Try a different tach or have yours serviced.