I have a 1991 L98 Tuned Port Corvette. When I turn the key to the on position the fuel pressure reads 50psi but falls back to zero within 2-3 seconds and the car won't start. I can spray injector cleaner directly into the throttle and the car will start, but shuts down immediately after the cleaner burns off. I've replaced the fuel pump, but that didn't help. Does anyone have a clue as to why the car is not maintaining its fuel pressure?

These pressure sensor for the whole fuel system is part of the low pressure fuel pump that is mounted inside the fuel tank.
*Note* You will NOT need to start the engine to do this test!
You will need a to do this! Do Not do it any other way as fuel systems can be at a pressure of between 50 and 60psi. For reference, car tyres are usually around 30 to 32psi. Plus remember this is Gasoline your working with!
The valve is located it the fuel line just before it gets to the actual injectors. It is positioned at the top left of the engine, Near the reservoir for the Brake fluid. It looks like a bigger version of the valve you use to blow up a tyre and it should be pointing directly towards you. I've attached a video of someone testing and replacing a fuel pump on a 2.2l Cavalier.
With the key in the second position, (Ignition On and the Engine OFF), you should be getting a reading between 50 and 60psi. You may need to Purge (Burp) the fuel lines of air if you have worked on the fuel system. This is done as follows.
Turn the key to the second position for 2 seconds then off again for 10 seconds. Repeat this 3 or 4 times and check the pressure reading on the test gauge. If it starts to show pressure repeat the above steps a few more times until it's high enough.
Once it's above 50psi AND staying there, Check in the engine bay and underneath the car for any obvious fuel leaks. Release the pressure on the Fuel Pressure Testing Tool and remove it. Don't forget to put the little cap back of the fuel line valve.
This is the point where you can try to start the engine. If everything is OK It should start quite quickly.

Not enough fuel pressure. Or the injectors are too small. I would lean to the injectors and the fuel you use.

Hi Patty,

It sounds like you may have a couple different problems here.

Firts, the stalling when coming to a stop problem is MOST LIKELY being caused by a bad Idle AIr Control (IAC). The 4.6L engines are known for these "sticking" and working intermittently.

As for determining if the fuel pump is bad, the fuel delivery system goes like this:

Connect a fuel pressure gauge to the service port on the engine fuel rail.
Cycle the ignition switch from OFF to ON. Repeat at least 3 times to obtain the highest reading.

The "Key-On-Engine-Off" fuel pressure specification is 35 to 45 Psi.

The fuel pressure should remain within specifications for at least 3 minutes after the key has been turned on. (the pressure will probably jump to 50 to 55 psi when the key is first turned on, then drop to within the specification in about 2 seconds after initial fuel rail priming has occured.)

If this is all good, your fuel pump and the rest of your fuel delivery system is good.

If the pressure does not reach the specified pressure or does not hold the pressure for 3 minutes, let me know and we will check further for the cause.

Hello and welcome to Fixya!
As a first course of action, I strongly suggest that you remove the positive batter connector and let it sit for atleast 5mins. before reconnecting it. This will reset the system and can get your vehicle back to it's normal operation. It can be a bad fuel as well so you may want to start repacing her with a fresh one.

Please do keep me posted on the progress. I'll be glad to help you out. Hope this helps and thank you for using Fixya! Have a good one!

You probably have a bad fuel pump. Get a fuel pressure gauge and check for fuel pressure at the shrader valve. Put the key to the on position. Your fuel pump should run for about 2 seconds. Your pressure should go up to 30-40 psi. If no pressure your pump is bad. Make sure you hear the relay come on, otherwise could be the relay. You should hear it click when you turn the key to the on position.
Joe.

it should only stay on for a few seconds,you have an underlying problem.it could be either your fuel pressure regulator or the check valve in the pump itself might be letting the fuel drain back into the tank,im guessing the car only does it after it has been sitting for a little while and after the initial hard start it will keep starting normally,the easiest way to test it is to put a fuel pressure tester on it and start the vehicle or just pressurize the lines by turning the key on and see if the pressure drops,if it does, pressurize the lines again and crimp of the line from the pump wherever it is rubber with a pair of vise grips and see if it drop then..if it doesnt it will need a pump if it does it will need a fuel pressure regulator,im guessing this car has a L98 5.7 ltr TPI engine in it

Most likely it's a fuel pump relay. It's on the panel under the hood.

38 lbs is not enough fuel pressure. replace the fuel pump

Do not attempt this unless you know your way around under the hood.
Use protective gear: safety glasses and protective gloves.
Somewhere on or near the fuel rail on your engine will be a plastic cap that is the same as a tire valve cap. Remove it. Underneath will be a pressure release valve, also much like your tire valve.
Cycle your key to the on position (not the start position) for 2-5 seconds. Turn key back to off position. Immediately go to the valve on the fuel rail and push the needle down. If the fuel pump is working, you shouls have fuel spray out of the valve quite quickly. The pressure in the fuel rail is about 40-50psi if the pump is working.
Hope this helps!

Check fuel filter on both vehicles...After that check fuel pressure ...Blocking off air flow to engine will change the fuel air mixture...air deprivation changes (lessens) air flow and fools engine into reading more fuel than is actually there. Mass air flow sensor should also be checked/cleaned if no results obtained by filter change if pressure is OK.