Finally ended annoying and flakey 740 problem. My 1992 745 with Rex/Regina had developed a habit of intermittent stalling upon acceleration. 192,000 miles. Sometimes it would die in the middle of the highway, or worse yet, at a railroad crossing. It would always restart. Replaced rpm sensor, injector ballast, checked idle air control...this went on for two years. Finally my Volvo mechanic had the same year Rex/Regina car available for parts. Checked voltages and swapped a used ignition module. It cured that problem, but started a new one. Intermittently and randomly, engine would not start. Discovered that if I connected a ground to the high voltage lead of the coil pack and let the spark leap to a metal engine or chassis ground, the car would then start and run normally until the next unpredictable instance of non-starting. Definitely an intermittent issue with the coil pack beyond any rational explanation.
I bought a used coil pack on Ebay and swapped it out. Problem disappeared. Car now starts every time. Amazing acceleration and better mpg.
Moral of this tale: The coil pack, and its very long lead to the distributor, could be the cause of intermittent and otherwise inexplicable problems that masquerade as other expensive issues such as fuel pump or ecu modules. . Only on the Rex/Regina Volvo. Ignition parts are hard to get because this model was only made for a few years.
You can get a used Rex/Regina coil pack on Ebay for $49 and a new one for $150. I keep a spare in the car all the time, along with spare ignition and fuel modules, and relays, especially the fuel injector ballast relay that can leave you dead in the road. I have also constructed a long spark wire that I can plug into the coil and ground out from the driver’s seat while I crank the engine. Beats reaching into the motor and pulling the greasy wire out of the distributor to check for spark.
Now that I have solved the problem, all this redundancy seems un-necessary, but I am determined not to be left stranded anywhere.