Pertronix 1761 Ignitor + 3.0 ohms coil, Tachometer needle jumping erraticaly

[jalexquijano]

This morning i decided to swap the ignitor installed on my 240z and after opening the distributor cap i notice something is missing, i guess it could be the ground wire,so i fabricated one with 2 terminals and installed a new pertronix ignitor model 1761 together with a 40511 new 3.0 ohms ignition coil.

 

The car cranked up fine, but whenever you step on the gas the tachometer does not read correctly. Once it reaches to 5,000 RPM it jumps to 7000 goes back to zero, etc. If you have the car parked and step on the pedal it raises to 5,000 goes back to zero. Bottom line it is not Reading as it used to read with the former ignitor. What could be wrong here? Could i have missed something?

 

I have attached pictures of the original 1761 ignitor and the one i just installed which is giving me problems. Your advice is highly appreciated.

[jalexquijano]

I just revert it back to the former ignitor an 3.0 pertronix coil and the tach is working as it should be. Could either of both coil or ignitor arrived damaged?

[jalexquijano]

It was a bad installation! Everything is working perfectly!! Some backfire from the muffler but its fine!

[EuroDat]

Looking at your second photo, the red wire going to the pickup looks chafed and maybe theinsulation is damaged.

Why did you change them, seems like your old unit is working ok?

The ground wire you made is not needed on the pickup version. Its a requirement for points systems.