Start Engine Problem

I have a Blazer 1998, S10, 4.3 Engine, 4 doors.
The problem is that some times the engine can not start.
The fuel pump was replaced and the problems appears every two or three weeks.
When the fuel tank is down the Engine start!!!.
The mechanic does not what happen because as I told you the computer diagnostic shown to replace the relay and I changed it and the problem persist.
The blazer works for two or three weeks and again the problem appears,
Any help is welcome.

Does the fuel pump run when the problem occurs? Have you checked fuel pressure? The OBD system does not monitor fuel pressure or the circuits that control the fuel pump. Those areas must be tested using other test equipment.

Does the fuel pump run when the problem occurs?
The fuel pump does not run when the problem occurs. Apperently the fuel pump is not running (Not listen)
Have you checked fuel pressure?
Not, I haven't checked.

When the fuel tank is down for check the pump the engine start with any problem.

How Can I check the fuel pressure?

Thanks for your response.

Check fuel pressure with a guage.

There is a scrader type fuel pressure test port on the pressure line going to engine.
Borrow or rent or buy a fuel pressure gauge.
Tape it to outside of windshield or outside mirror and check the fuel pressure when it no stats.
Also make you have spark to more than one spark plug to.

Hard to start cold or no start.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT