I am not an expert.
I have been watching many YouTube videos relating to C4 corvettes.
This guy at this link has a few c4 videos.
According this his videos, when the ignition is Turned Off, the fuel pressure (1989 C4) should drop Very slowly.


I would assume a 95 would also hold fuel pressure for several seconds at least.


Here is a better video, for a C4 LT1. Looks like you may have a bad fuel regulator.

My '95 will drop pressure slowly. I'm at 46 when primed and 38 while running. Could be the regulator or a couple other items. Replacing the fuel filter is cheap and not too difficult, FYI, easier done with crows foot wrenches.

Check out this site: https://axleaddict.com/auto-repair/H...sure-Regulator

Your diagnostics is moving in the right direction. :)

Why would the pressure hold for only 2-3 seconds? Shouldn't it slowly drop? Here is something that puzzles me. When I remove the gas cap and turn the key to on, I put my ear right over the hole in the tank for gas and do not hear any noise. Should't I hear the pump running?

When I turn the key to on I hear a buzz from the engine bay, not the fuel pump. The buzz from the motor only last 4 seconds. When it stops, the pressure drops to zero?
Any suggestions?

Hi Tommy:
The Fuel pressure drop is clearly a problem.
The fuel line should still be pressurized for many minutes after the key is turned off.

According to one of the videos, the Fuel pump has a check-value that will close when the fuel pump is off.
The check-valve many be located on the fuel pump.
The check-valve keeps the pressure in the fuel line from the pump to the Engine.

One of the reasons for the check-valve is to prevent the fuel in the line from draining back into the tank when the ignition is off.
When this happens, the Fuel-Supply line will become full of air.
The next time you turn on the engine, with an "Empty fuel line", the pump will pressurize the line with fuel pushed into a line full of Air.
Even though the line is now at 40 PSI, the line still has a bunch of air in the line.

As you start the engine, the first few feet of fuel line will be full of AIR.
It will take a few engine spins for the engine to suck out the air until it gets to the fuel.
This will cause hard starting.

Play the second video a few times to see how the example works.

When you say hard starting do you mean?
The engine needs to spin for 10-30 seconds and then it will start?
Does the engine perform Normally after the engine is running?
How is the Idle when the engine is cold?
How is the idle when the engine is hot?

There other reasons for the fuel pressure to drop very quickly.
Broken fuel line (with fuel leaking everywhere and an obvious fuel smell).
Many fuel injectors stuck Open (engine will run very poor, lots of gas smell from exhaust, etc.).
Broken fuel regulator valve that will direct Supply-fuel back to the tank through fuel-return line.

Thanks for your quick response. It takes sometimes 5-7 seconds for engine to turn over. I dot't like waiting that long in fear of beating up starter. So I try 2 or 3 times. This issue happens whether the car is cold or hot.

Once the car starts it runs stupendous. Idle is perfect both hot and cold. Acceleration is amazing.

I did have a friend come over and help today. With the key turned to on position, fuel pump kicks in but then stops after 4 seconds while the key is turned on. This is why the fuel pressure reading drops to zero.

With the key turned in the on position, shouldn't the fuel pump continue to run until the key is turned off?

Thanks
Tommy

Hi Tommy:

I have limited first-hand fuel pump experience (Any C4 fuel experts please jump in).
When the Key is On, the fuel pump will run until, "Some" part of the fuel system detects the correct pressure, assume 40 PSI..
Then the pump will stop when it reaches about 40 PSI, this is normal, Assuming the engine has not started yet.
The pressure should stay for hours at the same value "40", just as long as the Key is in the ON position.
The fuel pump will cycle on/off again automatically, when the pressure drops below a specific point.
When power is applied to the fuel pump the pressure should never drop below guess "30".

If you are saying:
While power is applied to the fuel pump and the engine has not yet started, the pressure increase ~40 and then quickly drops to below "30", while the keys is ON and the starter for the engine has not engaged?

If this is true you have a problem.

My best guess is the pressure-controlled switch for the fuel system is bad.
This switch may be located inside the fuel pump. (Any pump experts out there?)

The reason your car runs good after the engine is actually running is because the constant vibration is shaking the defective pressure-controlled switch and keeping the pump working for a while.

How can I tell if I have a P vin or a J vin? The vin number on the car gives me no indication.

If you have a C4, 1995, you have two engin options.
Send a Picture of your engine.

The 8th digit, Read from the Left, is the Engine type.
P = LT1 (300 hp)
J = ZR1 (405 hp)


https://www.corvette-web-central.com...INdecoder.html


8 Engine type: 8 = L98, P = LT1, J = ZR1, 5 = LT4, G=LS1, S=LS6, U=LS2, E=LS7, W=LS3, R=LS, 2014 C7: 7=LT1, 6=LT4

Thanks. Its P. I am thinking of replacing the fuel pressure regulator. Do you think it could be defective and thats why the lines wont stay pressurized?

Hi Tommy:
You have two problems.
#1 Fuel pressure drops very quickly.
Possible causes:
Bad Check value in Fuel pump.
The vacuum controlled Fuel pressure regulator stuck open.

#2 When Ignition is on, the fuel pump stops when pressure drops (while key is ON)
Possible causes:
Bad electrical pressure sensor switch, inside the fuel pump (Guess, I am not sure where this switch is located, most likely inside the fuel pump).

Your car is 23 years old.
If the fuel pump is Original, replace it.

Check the video links I provided and surf for more Regulators tests. I seem to recall there was a simple pressure regulator test on one of the videos.
While the Engine is Running, note the average fuel pressure while Idling.
Then disconnect the vacuum line to the vacuum-controlled Fuel pressure regulator.
If the pressure goes UP, it means the regulator is at least partially working.