Trigger Contact Points

[pbanders]

I pulled my dizzy this evening for an inspection, cleaning, and lubrication. While it was out, I did a bit of analysis of the trigger contact points that the ECU uses for injection timing, grouping, and engine speed.

The common terminal is 12, 21 and 22 are the points. Points resistance is about 0.10 ohms (from 21 or 22 to 12), measured directly on the terminals. Measurements at the ECU plug will register higher due to the harness resistance, but still should be under 1 ohm.

There is some slop in the mounting of the points to the dizzy body. I try to center them as best as possible. I wanted to determine the points closure characteristics, so I did two tests. To measure any overlap (both points simultaneously closed), I monitored continuity between 21 and 22, if both are simultaneously closed, I would see continuity. Nope, didn't see any overlap. To measure any dropout (both points simultaneously open), I connected 21 and 22 together, and monitored continuity between them and 12. If both points were open at the same time, I'd see an open. And I did - for 30 degrees of rotation.

My guess is that the flip-flop in the ECU never wants to see both switches closed, so the 30 degrees is a safety margin built into the cam profile. Also note that the cam is designed so that the low part (point "on") does not come into contact at all with the rubbing block. You can see this if you smear distributor grease on the whole cam surface, it won't be disturbed on one side.