look at fuel pump, fuel filter, and fuel pump relay. If it has sat for long time, may have clogged lines. If you check relay, and that is good, look at pump. If pump is good, look at lines. If lines are good, look at fuel dispursing system, (Carb,TPI, TBI, etc) If fuel is going to all places, look at spark. Pull plugs and see if they are clean. May need to search for photos of dirty spark plugs
was fuel filter replaced
Check for fuel and spark to the cylinders
If you are certain it is low fuel pressure and you've changed the pump and filter the next thing would be the fuel pressure regulator. Also check to make sure none of the fuel lines are crushed closed.
Make sure connections are on tight.
I have the exact same problem. After replacing the fuel pump everything was fine. Now the fuel pump does not always kick on and you have to turn the ignition on and off until you hear the fuel pump kick in. Went to start this morning and fuel pump did not kick in, still wont. So I checked the relays, all good. Now the fuel pump kicks on but it still wont start. Did the computer on this thing die?
Have you replaced the fuel filter? Are you sure the pump is running and the fuse is not blown or the relay is bad. Do you have fire, and do you have fuel pressure to the injectors?
Diagnosis: Engine Won't Start or Run Check related link below
Check the fuel pump pressure, the fuel pressure regulator may be bad. Need to know year, make, model and engine size to give you fuel pump specs.
Check for spark, fuel, compression Check ignition timing
If the engine turns over the batteries are fine. Diesels require special equipment to troubleshoot, take it to a shop that is competent in diesel engines.
It sounds like its not getting fuel. Could be clogged fuel filter or bad fuel pump.
i replaced the fuel pump and now my theft system wont work