96 cavalier cranks but doesn't start

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Ok so we just got this car it had a bad water pump so we changed that. Drove it for a few days and now it will not start. i checked spark plug 4 for spark and it had a spark. all the others looked cosmetically ok. i chaned the fuel filter, an i can hear the fuel pump. but the car will crank and crank and not start. i finally tried starter fluid and it still would not go.

thanks for the help.