97 suburban, 454, 4x4 hard starting.takes a couple primes of fuel pump to start.fuel pressure is 35 psi at idle.doesn't change when pinching return line.fuel pump was replaced 1 year ago.when cranking engine with fuel pressure gauge attached goes to 5 psi and drops when stop cranking.

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.

Does the pump stop running when you turn off the key? With electric fuel pump, the fuel pump relay sends voltage to the pump. The control side of fuel pump relay needs voltage and ground.
Engine cranking do you have spark at the plugs and fuel injector pulse? Use a gage and check proper fuel pressure, my info says 35--45 psi. Usually, if pressure is too high you check for a problem on the return side. If pressure is too low, you check the supply side of the fuel system.
Usually with initial prime the computer grounds the control side of fuel pump relay, for a couple of seconds, then w/o rpm signal, it shuts off. Maybe the ground wire is shorted to ground or problem with computer?

If your sending unit is one wire, unhook it from the sender and place a jumper wire from wire to ground. Turn ign on, gauge should pep high PSI. Two wire plug, place jumper between contacts of wires (unplugged). Same thing. What this does is isolate the gauge. If gauge pegs on test, replace sender. If it does it again with new sender, it's the pump. But it's probably the sender.

A fuel pump is the most likey problem, when you key-on a vehicle the fuel pupm turns on for 2-3 seconds to prime the system, it sounds as if your is not functioning properly. You can check fuel pressure at the schrader valve after pinching the return fuel line. You should have at least 35 psi, if not replace the fuel pump. Good Luck!

62psi keyed up and no less than 52psi in the run position. It will be hard to start with any less fuel pressure. Also the fuel pressure should not drop off quickly.

you might want to check your return line to the tank

Your choises are...bad fuel pump, restricted fuel filter (new?) bad fuel pressure regulator...out of gas....can you pinch off the return fuel line to the tank? some are rubber and some are hard plastic...dont pinch the plastic. This will give you the unregulated pump pressure. If it doesn't go up you have a bad pump or it's drawing air from the tank (pick up restricted/fell off or no fuel) if pressure goes way up and runs good your regulator is bad

Its your fuel pump.I had the same plomblem not too long ago.I was spraying either in to start it.I have a 97 chevy truck witch requires 65 psi to start and 55 to run properly.You need to find out much psi you need to start it.You can probaly look in your manual or just make a few calls.My truck had 55 psi and it ran fine i just had to get it running first.Good luck.I wonder if that fuel pressure regulator was a waste of time like it was for me.