Volvo Repair: hard starting, new distributor cap, pulling out my hair

Question
I own a 1989 740 gl and I am having a really bad time with herand it is driving me to pulling out my hair. She turns over but will not start, I have put in spark plugs,wires,new distributor cap,ignition module,2fuel pumps,sending unit,relayswitchand a fuel regulator. Everytime he fix her she will run fine for about  couple of weeks then she goes back to turning over and not starting. She will start in the morning 8 hours later she will not or she will start get me somewhere but when I get back she will not start not until 15-20minutes later. One day she just stopped on me while I was waiting for the light to change. She started back up 15 minutes later.It is qute obvious my mechanic is missing something what is it? Help please

Answer
Needs to check whether this is fuel or ignition related. When the car doesn't start , he needs to check for spark at spark plug and to see whether the plugs are wet or dry. IfWhen you crank the car to start and it doesn't,observe the tach to see if it moves even a little. If not check the crank sensor located on the top of the transmission, at the back of the cylinder head. It's not too expensive, I would just replace it if not already.
If no fuel, check the suppressor relay ( small black boxes by the coolant bottle ), the're both the same part numbers, try swapping them and see what happens.

Lastly if this car is non-california, there will be other items to check or note.
Let me know.