My (daughter's) Volvo '94 850 Turbo that has an intermittent starting problem.

The short version is that usually the car starts with no problem. But occasionally the car will crank fine but won't start. No sign of even trying to turn over, just steady cranking. This can go on for 10-15 minutes or for days (three and counting so far this time).

Towed it to our mechanic and left it there for three weeks and could not replicate the problem. Had it home for two days and wham, won't start. All connections have been checked.

The car is parked overnight on an incline and occurs mostly when the engine is cold (after sitting over night or at school all day). It happened once during the summer after being parked on level ground in a covered garage after sitting for an hour or two on a hot day. Took about five minutes or so of cranking before it started.

I was out there this morning (currently about 50 F) trying to get it to start. I gave up after about 10+ minutes.

I can hear what I think is the fuel pump running in the right rear after I shut the key off after each try.

I have tried pumping the gas pedel with no effect except to create a fuel smell, so I think gas is moving.

No CE light.

Any ideas on possible causes are most appreciated.
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Cheers, Fred