1996 GMC C1500 wont start

Engine would not start replaced fuel pump, and ignition coil, checked fire with spark tester was yellow so replaced coil. Still wont start poured a littloe fuel down the throttle body it fired but wouldnt keep running so we replaced the fuel pump. Still wont start and the fire is yellow at the coil. Also checked voltage at the coil was battery voltage and at the ign. Module also battery voltage. Im a desiel tewch for volvo and mack havent worked on cars for quiet a while this is my uncles truck. Thanks for any help Rusty