Car was not running properly

Hi Happy New Year to you all. When my car has warmed up and the engine is at idle .The re counter is constantly moving up and down.( To its normal idle position) It moves up and down by around 1/ 3 mmm.The car is running on Petronix ignition.Do you have any idea what might be causing this.? It has been happening around three months The Petronix was fitted maybe a year ago.Regards Nigel.

Hi Nigel,

did you also change power resistors and ignition coil? You should check which voltage amplitudes your old ignition and your Pertronix ignition delivers to rpm counter.

Hi Norbert.YesI did but with a new standard Bosch coil .Today I tried a Blue Beru coil which I have run with in the past ok.Although the issue seemed to be slightly worse with the Beru.Would what I mentioned have an effect on the general running of the car ? I just wanted to check if this might be my ongoing slight feels like intermittent misfire I'm getting.before stripping the injection to replace the bottom and middle seals Unfortunately for me I'm rubbish with electrical testing unless I call a professional to check.Regards Nigel.

Hi Nigel,

1. I am Volker and not Norbert

2. Ignition coils are not selcted by color. They have electrical values and they often need power resistors to work properly. Coild and resistor must match. You change voltage level on primary coild side. Your rev counter wants to see original amplitudes.

Hi Volker.Sorry for the muddle up of names.My car has never had a visible ballast resistor .If this is what you mean.I know the earlier versions had it mounted on the coil. As far as I know ( which is not much) I don't think either coils are high performance versions.As I'm getting this slight miss with both coils .can I assume these are not the issue.and is more likely to be an air leak at the injectors? Regards Nigel.

Hi,
it seems that there were different versions of ignition coils. Up till 6/73 Bosch had supplied a coil and power resistor. After that it was without.

Which coil no. do you have?