Volvo: volvo not starting, volvo 240 glt, volvo 240

Question
hi i own a 1988 volvo 240 GLT the problem when i try and start the car the engine is turning over but wont start and if i leave it alone for approx half an hour it starts with no problem this does not happen all the time but you can never tell when this is going to happen it could run perfect for a week or a few days and it happens again i have had a brand new in tank fuel pump fitted fuel filter and the main fuel pump please could someone help

Answer
Steven,
When the vehicle is not starting test the fuel pressure making sure that it is no less than 42 psi. Fuel pressure ok test for spark. Has the engine had a recent tune up are the plugs in good condition? How about the cap, rotor and wires? Have they been tested? IS the main wire harness in the engine compartment showing frayed wires?