Chevrolet Repair: 1999 astro van will not start, astro van, port injector

Question
HI , I have a 1999 astro van, the fuel pump went, so we changed it, it started right up ran for a hr then we shut it off, after that it only has started 2x & you had to turn it over for a while till it caught, now it will just turn over, the fuel pump has since been replaced along with a filter(pressure is fine) only thing other than sensors that have not been changed are the plug wires, the pcm has been scaned & comes up with a security issue, when cleared it still does not start, a new pcm has been added, still not starting, spark is fine, even has a new coil.
basically it has fuel & spark but will still not start, other than changing sensors such as the map, i am not sure where to turn, as everyone i know has a diff (change this & it will start) attitude, is there anything you can think of for me, any help would be apprecitated.
thanks for your time.
jason

Answer
First of all you state you're getting fuel pressure. Are you getting enough pressure. I'm assuming you have a 4.3 with a Central Port Injector System (you have not told me)? With the key cycled from lock to run, does the fuel pump run for 2 seconds and does the fuel pressure reach near 60 psi and hold? You need a high fuel pressure to open the poppets on this injector unit. If it does not have the proper fuel pressure you'll need to diagnose and repair that.

IF fuel pressure is what I stated previously, crank the engine over and watch the pressure. The pressure should stay around 55 to 61 psi. If that's ok and you say you have good spark, I would check to see if the engine is not flooded. The CMFI units have been known to fail causing a dumping of gas into the cylinders. Try unplugging the connector to the CMFI unit, hold the throttle to the floor and crank it over to see if it wants to start. You can also pull the spark plugs to inspect.

Also if this vehicle has a pulsator coupling attached to the fuel pump, it should have been replaced with the fuel pump. pulsators that have an orange inner seal leak. The new pulsators are black.

Hope this helps, fell free to get back to me.