fuel pressure engine running is and when the engine is shutting down fuel pressure is ??? - will that engine hold fuel pressure - Key on engine off ? Is the fuel pressure steady and at the proper psi ???

KEY words from you the fuel filter is half full - so the fuel pumps can not keep up delivering the correct amount of fuel flow. You have a fuel delivery problem - and its to weak from either the fuel pumps or the delivery of fuel threw the fuel system - restriction or a voltage problem or weak fuel pump(s). Possible restricted fuel pump or going bad.

Fuel samples ? clear jar fuel inspection for water and condition is ??? How old is fuel and does the fuel sample have water in it ???

- run on a remote fuel supply all new and fresh fuel. use a primer to prime the fuel system and squeeze it when engine is shutting down - did that help ???

constant 12.7 V to 14.V when engine running and what is voltage when the engine shuts down and how about voltage before the engine even is started ?

Lastly scan engine and know how to read it.

My guess running out of fuel - fuel pump(s) or a fuel delivery problem is mostly likely your problem - these others tests should pin point problem to find exactly what it is or not just one but more than one.

IMO without doing any of these tests - might as well pull out the dart board and throw darts at it. You have to test to pin point the problem area(s)

Do you have a genset? is the problem engine on the same tank? If so it might be sucking air through the genset if check valve is bad

No gen set either...did a couple test today

Switched water sepator with one of the running engine
Started right up and same died again after 30 some seconds
Opened both gas cap, started 30 seconds and died
Took the hose off of fuel tank and put it in a separate 2 gal gas tank, same again
Blew some air backwards in the fuel tank and vent works well
So im down to fuel pump, or pumps? Is there one? Or two?
Or might be the iac valve as previously stated... Where is that iac? Right after the air filter? Or right side of plenum towards the back? Seems like there are 2 or more sensors...
Guess ill have to bring it to the doctor! Kind a miss my carbed engines! At least i was able to play on them by myself! But not anymore...

To rule out the iac you can either swap them out left to right and test or bump the throttle when you start. See if it will run at 2000-2500 rpm. My guess is iac is fine. Usually with a bad one, it won't usually fire.

My 500efi's IAC sensors went bad and did the same thing, started up and stalled out shortly after. Replaced them with the black GM version not the expensive blue Mercury and they ran perfect. Search on here there are some other threads with more details.

Hmm first time I've heard that. I've had Iac's go bad and motors wouldn't turn over at all.

Going back to what was posted by the OP - his fuel water sep filters were half full or half empty how ever you want to look at it - when he took them off ( HIS WORDS) This is not telling you something. Really - its called a fuel delivery problem If the fuel filters were half full that means right after the fuel filter no other fuel systems were getting any fuel since it could not keep the filter full. - HENCE ENGINE SHUT DOWN. .Would this not be the logical place to start testing and narrowing that down first ???

Anytime you remove spin on fuel filters the fuel should be pouring out when you start to unscrew them half way. His was half full of fuel when he took them off - per his words. Is this still correct if you pull off the fuel filter right after engine shuts down ?

What is fuel pressure readings ??

If you pull the filters again right after engine shut down and they are only half full - YOU HAVE found the problem.

He wrote 3/4 full and did not specify how long after shutdown he removed them......

The majority of my multiple vehicles fuel filters are not overflowing when replaced, yes some have been but I normally don't remove immediately after shutdown.

I agree that the fuel system is one option to look into, along with many other good options on this thread.

Where is that iac located?

How does the motor start up after it stalls. Can you just cycle the ignition and it starts for another 30 seconds or do you need to manual (pour gas in the filter and replace) fill the fuel filter and then start it? You need to borrow a scan tool to check pressure. When you figure it out please make sure you let us all know LOL. You do know there is a barrel fuel filter as well close to the fuel rail?