1988 E-150 Problems

I Got this Van about a month ago and it would not start. My dad had the van and he said that he just came out one day to leave for work and it did start but died and then took about 5 min. of turning the engin over and he got it started again but only made it a block be for it died again and has not started sence then. I have changed the Distributor cap and rotor. I have also changed the fuel filter and the fuel pressur regulater. and the van still will not start. Any body got any i ideas. :banghead: