Volvo Repair: 1988 240dl will not start sometimes but will others., volvo 240dl, vapor lock

Question
Hi phil.
My 1988 volvo 240dl with 89000 original miles has recently become hard to get started some days and will start like normal at other times.  It seems almost like vapor lock or something.  I am beside myself.  The car has always run like a champ until about 2 weeks ago.  yesterday I tried to start it, and it will turn over alright but wont fire.  about an hour later I tried it and it started fine.  This morning I tried and it wouldnt start.  I have changed the air filter and that is all so far.  Your help would be greatly appreciated.  Only routine maintinace has been done to this point.  thanks.  

Answer
There are several possibilities but they are have to be checked to confirm and isolate problem. When this happens, need to check to see if there is spark to spark plugs. If there is, then need to check if fuel pump is working by listening for buzzing noise from under car while cranking.
This helps diagnosis since you'll now know what circuit to concentrate on.
Also hope you have at least 1/2 tank of gas because when low the gauge is not very accurate.