Intermittent Start
 

I bought this car two weeks ago and now the thing isn't starting at all. I've worked through the fuel system and it's getting gas, It's getting air, but there's still a no start condition. The OBD2 port loses communication with my tool intermittently and won't display I/M monitors.
Checked the continuity of all the sensors with a circuit tester and a multi meter, everything checks out just fine. This problem is somewhat mystifying to me. Any help is appreciated.

fuel pump relay

So I took the car to a local Volvo expert, and he took one look at the car and said "ECU." He promptly pulled the box to the ECU apart, cleaned and resurfaced the connections and sprayed conductivity chemical on the connections before boxing it all back up and making sure there was a hose connecting the ECU box to the radiator shroud.
Now it starts and runs fine.
I have never seen anything like this before.

The OBD2 will show diagnostic codes for communications errors - but not all tools read all codes. My bet is he used a better scanner and saw the error code.

Update time:
Well, months later and it still starts and runs fine.
*Knock on wood*
Hopefully this is the last I see of this particular problem. In the future (probably a year or so down the road) I'll be looking into an upgraded ECU. The power gain opportunity is just too tempting.