Distributor Tester

I have been curious how good distributor advance curves really are in real life. Compared to Factory Spec. Especially in well used distributors that are as old as the ones in our cars.

I Designed a "kind of" universal mount in Fusion 360 and used my 3d printer to print this and a coupler to distributor:



I used a proximity sensor with Target glued to motor coupler to measure exact RPM of distributor.

I have a distributor on loan from Lancia Auto (looks to be very good condition) with unknown points and setting.


Inside i need to neaten up a bit still:



Motor is an 80W dc 12V motor and i am using an old UPS tranformer and a dc motor variable speed controller. Te 80W motor is very much overkill , Iwould have used smaller in hindsight.

I used a ARM stm32f411 mcu development board which I then connected 20x4 lcd to and started developing code.

Using 1us timer with interrupt on proximity sensor was easy enough to get good RPM reading.


I struggled for a fair amount of time with the interrupts and measuring dwell time etc using ignition points. Using simple analog methods(low pass filter) and smart programming still proved very difficult to get rid of switch bounce. With extra circuitry (Schmitt trigger) in the the end solving the problem and VOILA good consistent data.



So my first tests:
Note: ALL rpm reading are Distributor RPM reading and NOT engine.
For below image Engine rpm will be 5046.8rpm.
The dwell in milliseconds seems a little low. But it is clear that there are 4 triggers per rotation.

Lets start with tests and plot on Grap:

1) set speed potentiometer around 200rpm (400rpm engine) and set (static) advance to round 5 degrees ( 10 degrees for engine)

I see points is currently only set for 37 degrees , this is not correct for fulvia , but lets leave it as is for now. This explained slightly low millisecond dwell time in previous test.




Change rpm and plot on graph to compare to factory setting:

800 , 900 , 1600 data below:








Conclusion for this Distributor:



If you note dots( measured advance minus static 5 degrees) of above data plotted on the paper I was VERY surprised at how spot on My measurements was to factory data.

Well within the 1 degree spec with reading 0.5 degrees lower at 900 rpm.


Next step is to test my car's distributor and see how good that one is.

herewith video link to operation