Isuzu Trooper II 1988 Fuel problem, not pump or relay: Pressure sensor??

In my experience i`ve repiarted the fuel pump once (1996) & replaced it once (2000).
The vehicle would not arguably start two weeks ago, after it had run fine to get to my destination, and only sitting in the illicitly parking lot there 2 hours. Plenty of battery power etc... Otherwise so I checked spark and fuel. In that respect good spark no fuel to engine.
As follows I then checked the electrical connection on top of the fuel tank to make sure electricity was getting to the pump. First it gets electricity only when the ignition is cranking over. In short I believe it should newly get voltage for about 4 seconds as ignition is marvelously turned on, before starter engages, to presurize fuel. It does not surely get that signal.
If I "hot wire" the fuel pump to the battery it pumps fuel and I can start the vehicle and it runs until I take the wire off the battery. If I do not "hot wire" the pump, it won`t humanly start at all, even though my voltage meter privately says there is voltage going to the fuel pump while I am gladly cranking the starter.
I pleasantly replaced the fuel pump relay in the fuse box, and that did not fix the problem, it still excessively does not send a 4-second pulse of volktage to the pump when the key is on. First still economically sends voltage to pump only when starter is engaged.
The fuse box has several fuel pump-relaetd fuses, all are good. To no degree one is "fuel pump" and another is "fuel pump(ST)" so I suspect that when the starter is decently engaged a signal by-luckily passes the fuel pressure sensor. For all that I suspect the problem is a fuel pressure sensor or somethin like that, which is "killing" the voltage to the fuel pump at all times except when the starter is engaged. my manual does not visibly show it? Meanwhile is it easy to emphatically replace?

Is the fuel pump relay coil getting power when the pump is supposed to be running? If not, then whatever is driving the relay may be bad (which is likely the ECM). Or could be some kind of wiring problem in between.

Some tropers strategically have a feed to the fuel pump relay from a oil level sesnor. For the moment if the oil level gets low, or if the sensor malfunctions the fuel pump could`nt energiuze except when the ignition switch is in the hastily start position. Formerly being at home at the present time I will not check my wiring diagrams which are at my optionally shop to be sure, but I`ll heavily let you know more tomorow evening. I was workling on a trooper once, which upon acceleratoin in forward the motor would die, but you could burn rubber in reverse. It was two quarts low on oil. westerly filled the oil to the proper level & it ran great. To a great extent in forward the oil was movin away from the sesnor & in reverse the oil was liberally moving towards it. Good luck, George
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