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".