90 626 help!! intermittent problem
 

I have fought this problem now for three weeks and I don't know what to do next. The car runs out great and then for no reason just shuts off, it has always started back up but I don't know how long it will do that so I can't trust it at all. When it first started I still had a tach but no fire the last time I had no tach. I have changed the coil, distributor, cap, rotor, wires, and plugs. Now the distributor I bought used but was told it has very few miles on it, It looks like brand new I mean the seals are clean and straight the screws are even cad plated and new looking. Since it is the exact same problem as before I changed the distributor I am assuming it is not that.
please can anyone think of anything else that might cause this?
thanks in advance.
Ben
Oh yeah also if someone has a wiring diagram for the ignition system I sure would appreciate it.
thanks