hope this helps someone out.
Ive been using it for trouble shooting my 89 Raider.
Ive been researhing on here and google for a while and just wanted to give back.
http://easyautodiagnostics.com/mitsubishi_ignition_distributor/ignition_spark_tests_1.php

Thanks Kane
That information may come in handy someday. <img src="/forums/images/graemlins/kewl.gif" alt="" />

very clear and informative site, thank you.
I email a couple questions to him.
The '89 has a different LED / disc module than 90-94.
My understanding was the tiny slots along the edge signaled injectors,,,and large slots near center told TDC or crank or cam or all 3.

Also on '89 (013 disc) there is no blank space on the edge like on the 90-94. What does this mean??? I'm thinking TDC on #1,,,but what signals the '89 of TDC.
This has always mystafied me, but I must admit I'm not the sharpest knife in the drawer.
I've never been able to get a smooth idle. I have washed my engine , but have changed plugs wires and cap/button since then.
Maybe just a tired engine , off compression engine <img src="/forums/images/graemlins/frown.gif" alt="" />

P.S. - I've also ?wondered? if you could have a "dim" not quite burnt out LED in the module that made things "not quite right".

Just glad you guys could get some use out of it. I was ready to beat my head against a wall while trouble shooting my ignition system. In the beginning I thought "ok, Ive got 12v to the coil why isnt it firing?" little did I know about all t he other sensors that come into play.
As to the previous posters inquiry about the optical sensor- I am very lacking in knowledge to the way that the sensor reads the disc on different year models. If I come across some more info as to the internal workings I will be sure to post it up.

Happy trouble shooting!
Kane

As I understand it, there is a coarse wheel (6ish slots) and a fine wheel (lots more slots, can't remember how many). The coarse wheel indicates top dead center for each cylinder, and the fine wheel indicates where the motor is between each cylinder's tdc. The coarse wheel controls injector pulsing, and the fine wheel controls ignition advance. The missing slot indicates tdc on #1. All this is combined with the rpm signal off the coil - for both timing purposes. Math logic in the ecu then schedules the injection and spark events per the spark advance tables built into the ecu, influenced by the ect and maf and baro and iat sensors and the tps.