1991 astro . 4.3 135000 miles . turns over wont start. cranks and has spark but wont start. if you put gas in fuel injector ports starts and dies. pulled fuel filter off and was clear. bad fuel pump or relay i guess. cant find relay location how do i test the fuel pump? or should i just replace fuel pump?

You say it is getting gas, do you know for sure that gas is getting past the injectors ? And do you have normal fuel pressure, compression, and spark at the plugs ?

Are you getting spark to the plugs and do you have fuel pressure at the injectors ?
Can you tell if the pump is running when you first turn on the key switch ??

Sounds like a bad ignition module. The module does two functions. It runs the ignition coil and also delivers the signal to the ecm to run the injectors. Sounds like it isn't putting out a tach signal.

Try starting it with the throttle open all the way. It may have to much fuel in the cylinders. If it acts like it wants to start or starts and dies replace the spark plugs, they are probably gas fouled.

There is a sensor under the left hand side of the dash that would not allow it to start, provided that you have replaced the electronic spark module inside the distributor first, which is what it sounds like it would be, When you say you replaced the distributor I assume you replaced it complete!

replace your injectors. your vehicle is getting the fuel to start from the starter fluid. however the injectors arent giving it the gas that it needs to stay cranked

sounds like bad gas, i would put some fuel cleaner in it ( I use Seafoam) and try that

fuel pump is a good place to start

Could be Lots of things Causeing that Frist Could be a Cracked Spark plug and Be your Timing out on it also could be Vacume Leack EGR stuck open or Closed Bad Wires Emissions Control System not workin Right

please.. 1991 chevy lumina..mech has car for 4 days..
repl ICM.ECM..checked ..all fuses.cranks..no run..smell fuel.
says spark good.Fuel press @ 42. put light on fuel injec sensor
..tells me weak signal( light shud be brighter) .Says it ran once
in 4 days for 2 min & died..." tells me injectors not accepting fuel