Mazda Repair: engine cuts off, mazda dealer, mazda protege

Question
I have a Mazda Protege 1991.  In the past 3 months, it died on me 5 times,always after 10-15 minutes of driving.  It feels like I just turned off the switch (no sputter, no sign, no warning).  When I try to restart right away, it will just turn.  It will start again after 20-30 minutes.  Always starts well in the morning.  Put new fuel pump and fuel filter, did not help.  Brought it to a Mazda dealer.  Could not read any code, and did not do any further investigation.  Any idea what I could try to fix it myself?
Thanks,
Luc

Answer
When it fails like that again you need to preform a spark test to see if the ignition is firing.  The symptoms sound like a failing coil however I believe that car uses a a dual coil set up if so it would fire on 2 of 4, its not in my normal area of expertise so just some suggestions.