1990 subaru legacy new fuel pressure regulator, and fuel injectors wont hold pressure checked fuel lines by pinching engine side of pressure gauge holds just fine so i believe it's in engine can't smell or see any gas comming from fuel rails and as i said i just replaced injectors

Fuel pressure may drop due to a leaking injector or bad check valve in the fuel pump itself. The regulator does not come into effect until the engine is running and a vacuum supply is produced to it. If the regulator is leaking internally, it could send fuel back to the tank as well. Prime the fuel line and pinch off the return line ( if possible ) to eliminate a regulator problem. If the fuel pressure drops with the return line pinched off, suspect a leaking injector or fuel pump. If injector is leaking, the vehicle should run rich and cause a hard start/rough run condition

You should have a test port on the Fuel Supply rail, use a tool from a local auto parts "Tool Loaner program" where you can borrow tools for free,w/a deposit of course,then follow the steps provided;

MPI Fuel System Pressure Test

The MPI fuel system used in vehicles equipped with a 4.OL engine employs a vacuum balanced pressure regulator. Fuel pressure should be approximately 55-69 kPa (8-10 psi) lower with the vacuum line attached to the regulator than with the vacuum line disconnected. System fuel should be 214 kPa (31 psi) with the vacuum line connected to the regulator and 269 kPa (39 psi) with the vacuum line disconnected. CAUTION: Some fuel may be discharged when connecting fuel gauge to fuel rail.

1. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to test port pressure fitting on fuel rail (Fig. 7).
2. Remove vacuum line from pressure regulator.
3. Start the vehicle.
4. Note gauge reading. With vacuum line disconnected, fuel pressure should be approximately 269 kPa (39 psi).
5. Connect vacuum line to pressure regulator. Note gauge reading. Fuel pressure should be approximately 214 kPa (31 psi).
6. If fuel pressure is not approximately 55-69 kPa (8-10 psi) higher with vacuum line removed from regulator, inspect pressure regulator vacuum line for leaks, kinks or blockage. CAUTION: Fuel pressure will rise to as much as 655 kPa (95 psi) when the fuel return tine is pinched shut, shut engine down immediately after pinching oft fuel return line.
7. If fuel pressure is low, momentarily pinch shut the hose section of the fuel return line. If fuel pressure remains low, inspect the fuel supply line, fuel filter, and fuel rail inlet for blockage. If fuel pressure rises replace fuel pressure regulator.
8. If fuel pressure is above specifications, inspect the fuel return line for kinks and blockage.

Capacity Test

1. Remove the cap from the pressure test port in the fuel rail.
2. Connect a 0-414 kPa (0-60 psi) fuel pressure gauge to the pressure fitting on the fuel rail (Fig. 7).
3. Start the vehicle. Pressure should be approxi- mately 214 kPa (31 psi) with the vacuum hose connected to the pressure regulator and 269 kPa (39 psi) with the vacuum hose removed from the pressure regulator.
4. If the pressure is not to specification, check the following before replacing the fuel pressure regulator:

• 4a - Inspect the fuel supply and return lines/hoses for kinks or restricting bends
• 4b - Check the fuel pump flow rate. A good fuel pump will deliver at least 1 liter of fuel per minute with the fuel return line pinched off. If the fuel pump does not pump adequately, then inspect the fuel system for a plugged fuel filter or fuel pump inlet filter (sock). Fuel pump flow rate can be done by connecting one end of an old A/C gauge hose to the fuel test port on the fuel rail and inserting the other end of the hose into a container of at least 1 liter capacity. Run the fuel pump by installing a jumper wire into diagnostic connector terminals D1-5 and D1-6. Be sure to pinch off the fuel return line or most of the fuel will be returned to the fuel tank.

On the 2.5 engine the fuel pressure regulator should be mounted on the end of the fuel rail where the hose connects.
It has a vac hose going to it.

Check the pressure to the fuel rail then check it at the line before the fuel pressure regulator, it should be between 55 and 80 psi at the rail and 100 psi before the regulator, if you don't have pressure before the regulator then you have a fuel pump issue, if the rail pressure is low then you may need to replace the regulator.

Its possible that your crankcase is full of gass too, I suggest change oil and filter, also, if it wont go over 40, the converter (catalytic) is probably damaged as well, raw fuel in the exhaust will break up the cat. Oil change is imperitive as too much liquid in the crankcase will destroy an engine in seconds. Can also be caused by the clogged converter, too much backpressure.

Get a vacuum gauge, hook into a manifold vacuum source. Increase RPM to 1500-200 and hold steady, if vacuum gauge falls, exhaust sytem has a restriction, the cat or muffler or a pipe has a broken chunk of the cat blocking it.

Hope helps; keep us updated.

If it acts like it is flooding while idling, but it runs fine on the road, it could be running too rich and flooding it out due to leaking injectors, bad fuel pressure regulator, or excessive fuel pressure.

I would start by replacing the Fuel Pressure Regulator since it doesn't cost as much as the injectors.
Check your fuel pressure using a Fuel Pressure Check Gauge to see if the fuel pressure regulator is maintaining the proper pressure.

Vacuum is attached to the Fuel Pressure Regulator to control system pressure. When the fuel pressure regulator is not functioning properly it causes the fuel pressure to be above normal operating pressure. This condition causes excess fuel to be injected causing a rich mixture that produces black smoke.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Check for a very dirty air filter or an obstruction in the air intake. (Engine not getting enough air so mixture is too rich.) Check for fuel pressure to be correct and not too high with the pump running. If it is too high, check that the fuel pressure regulator is working.

Try this: connect the fuel pump but disconnect the cold start fuel injector. If you can get it to start and run, then fuel pressure being too high is most likely. When the cold start injector turns on, the extra pressure is causing more fuel to flow through the injector than normal and the engine floods out.

but if you have no fuel pressure it wont start. Spray some quick start. If it starts then you need to test for fuel pressure. If none or low, replace fuel pump.

The fuel pressure should hold at or near the 45 lbs after you shut the truck off.
You have one of three problems causing this.
One, the fuel pressure regulator is leaking internally and allowing fuel to return to the tank via the return line. To verify, use a pair of pliers and gently pinch the return line off. Turn the key on to the run position, the pump will run for 2 to 5 seconds and pressurize the line. Watch the pressure gauge, it should hold pressure. If it does, change the regulator.

Two, the check valve at the pump is weak. To verify, turn the key to the run position, when peak pressure is reached, gently pinch the pressure line and watch the pressure gauge. If the pressure remains near the peak pressure the check valve is bad. Replace the fuel pump.

Three, if neither of the above procedures work, you have a leaking injector. You will want to remove the fuel rail, pressurize it to find the bad injector.

Any one of these failures will cause the "vapor" issue you describe.

Good luck, let me know what you find.
Regards,

measure fuel pressure with engine idling the fuel gauge should read 20-24 psi if not within specification replace the fuel pressure regulator.