Volvo Repair: Engine Performance, fuel pressure regulator, rear muffler

Question
I have a 740 Turbo Wagon...it has been sitting approx 6 months and had to have an exhaust system installed and several vac hoses reinstalled. with the rear muffler and pipes missing and the vac hoses disconnected it run fair...when the exhaust  and hoses were reinstalled it now runs very very rich, black smoke pours out the exhaust and will stall itself out on a full throttle start and has no power at all. the car has approx 225,000 (and up until now has run like a charm) and has been maintained well all these years.
I am guessing O2 sensor? who knows any guidance would be greatly appreciated, the car is going back in to daily service and needs to run good for at least another year or two....regards david

Answer
Hello David,  Don't overlook the 'fuel pressure regulator'.It is located next to the front of the engine by the oil fill cap.It has a rubber diapham inside and it may be leaking.Take off the vac hose and check for any presence of fuel,if any, replace it. To properly wake her from her beauty sleep,change the oil and filter (Mann or Volvo Only),fresh fuel filter,air filter and spark plugs (Volvo, NGK's or Bosch Only) and lastly a thermostat.Then let her run 1 hr. at a time then off for 20 min.s then run another 1 hr. Add 1/2 Qt.of trans.fluid to the fuel,it will clean and free up the fuel injectors.After that,turn the key,think good thoughts and Go!! Thank you and good hunting!  PKD