Since I noticed this was in the faq, I'll add:What the ICM, or "igniter" really consists of is just a high-speed relay.
It switches ground on and off as per the computer's demand.
The computer takes the signals from the CKP, CYP, and TDC sensors, combines them, and sends a signal to the ICM to tell it to fire spark at a certain rate.
The ignition coil has 2 inputs and 1 output (coil wire that goes to cap, sends spark to rotor button). On the external ignition coils you find on US preludes there are 3 wires on the connector, two of them are just connected internally, the main power feed comes into the coil, then the coil splits it out to power the distributor as well.
The other wire is the signal from the ICM, notice that there is no constant ground input.
The coil always has power to its positive terminal, and the ICM switches ground on for just an instant to fire a spark. This of course happens at very high speed, which varies with RPM.
If anyone here can answer why the coil switches on with ground instead of power, other than the fact that the jumper is needed to power the distributor (because that isn't the reason), I'll give them an e-cookie. Hint: Think of current flow.
-Matt
███| Quote, originally posted by Archidictus » |
| Only a fool dismisses the forest because of a fallen tree. |
