Fuel pressurre specification

It sounds like there are multiple issues with your Isuzu KB 240 LE. A powerless engine and stalling can be caused by a number of issues, including:

1. Fuel Delivery: If the fuel pump is not delivering enough fuel to the engine, it can cause a loss of power and stalling.
2. Ignition System: If the spark plugs or ignition coils are not functioning properly, it can cause a loss of power and stalling.
3. Mass Air Flow Sensor: A faulty mass air flow sensor can cause the engine to run lean, resulting in a loss of power and stalling.
4. Vacuum Leaks: A vacuum leak can cause a loss of power and stalling.
5. Throttle Body: A dirty or clogged throttle body can cause a loss of power and stalling.
6. Engine Control Module: A malfunctioning engine control module can cause the engine to lose power and stall.
7. Fuel Injection System: A clogged fuel injector or a failing fuel pressure regulator can cause the engine to lose power and stall.

It's recommended to have the vehicle professionally diagnosed to determine the root cause of the problem. The diagnostic process may involve checking the fuel and ignition systems, performing a vacuum leak test, checking the throttle body, and possibly scanning the engine control module for codes. Once the issue is identified, the necessary repairs can be made to restore proper engine performance.

Automatic transmission ??
Check engine lamp illuminated ??
Cold engine idle speed ??
Warm engine idle speed ??
IAC (Idle air control) system operation ??

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The fuel filter light comes on to tell you that there is Water In The Fuel tank at a level high enough to be picked up by the fuel pump. Your problem is a fuel delivery system that is full of water. Drop the tank and clean it out first. There is a very specific procedure for replenishing the fuel system with good fuel. The best thing to do is pick up a copy of Haynes Diesel Engine Repair Manual, Part #10330 as it outlines the procedure. However, if you are unable to get the book reply in the comment section and I can type it out for you. It requires 14 steps.
While you are doing this it would be a good idea to also replace any and all rubber pieces of fuel line. They have been known to collapse over time, when the pump comes on. Make sure you get fuel line that is diesel specific, regular gas line won't work. You mentioned replacing the injector pump so it will need to be taken to a diesel shop to be re-timed. Timing involves tools that are expensive and not normally accessable bu you and I.
The Hanes manual is an excellent investment at about $22. It provides excellent repair procedures for your engine as well as some service up-dates and shortcuts.

Replace the spark plugs and get the ignition timing checked and corrected. Get the specific gravity of battery checked. Check and if required replace the fuel filter.

It is located on top of the fuel sending unit on the fuel tank. The tank needs to be dropped in order to service the pressure sensor. It's not real common for them to go bad and there are several other possibilities that can make this code appear. It may be worth checking them out also. It would be nice if you could oust the actual code you are getting also.

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you might not be getting enough fuel pressurre check your fuel pump

Sounds like fuel pump may be going out. Check fuel pressure to see if it is within specifications and steady pressure. Next time car stalls, lightly bang on the fuel tank with a rubber mallet or screwdriver handle about 10 times, then try to restart the car. If fuel pump is going out, this helps "free it up" and the car will start. It will only last a short while though and stall again.

Not much to work with here. Can you be more specific? Does it stall at random or at certain times? Stopping? Taking off? Is the car fuel injected or carbuerated?

The ignition timing is not advancing at higher rpm.

That is the job of the ECM (Electronic control module).

Inspect / replace the ECM.

check the idle sensor and map sensor