I replaced my dizzy o-ring and reinstalled it in the same location. How do i check my timing? it's a 1990 3.1L EFI RS.

 

Buy or borrow a Timing Light ~40$.

 

Also, you need to unplug the ECM timing advance wire, to get accurate timing at idle. It's a one-wire plug, tan wire if I remember correctly, and it should be sticking out of the wire harness near the A/C blower box. This will keep the ECM from adjusting timing, similar to unplugging the vacuum advance on an old school distributor.