Volvo Repair: 1989 Volvo 740, volvo 740, stage unit

Question
Symptom started 10/10/08 .Vehicle will stall intermittently, and some times will not restart until allowed to cool down at any time any place. fuel press. is always steady at 40-45psi. Fuel filter was replaced. Ign. fire was not present when testing was able to be performed. Coil had B+ on both primary posts, but no pulse while cranking, when engine did run pulse was present. So CKP was replaced no help. ECU was replaced w/ a used unit (Sorry $50 is better than $900), and vehicle ran good until now 11/17/08, symptoms are back, I've heard of engine harness issues, any suggestions?  

Answer
Casey, can be an intermittent Speed sensor or ignition power stage unit.  It may also be a harness issue.  Best way to test is with car running and granb harness from behind cylinder head and move up and down.  If stalls, theres the problem.  Hard to say without inspecting the car.  Roger