My guess would be the fuel pressure regulator. The pressure at the rail should hold post shutoff with a drop of only a few pounds. On the 99 it is inside the intake manifold so a bit of a bear to get to. I thing the same on yours as you have spider injectors as well? An injector leak would show up on the plug with the leaky injector.

 

Thanks for the answer, yes it's inside the intake plentum. I have removed several times, replaced a couple puppets and tubing. Have not piled plugs science early summer when I did compression test to check break in. They were fine then, but am going to pull today. If I need to replace pressure regulator am going to just replace entire spider assy. Have seen for fairly reasonable, and rebuilt under 200$ but they scare me, I realize some just pull and clean off and call rebuilt. I guess a porely operating pressure regulator may explanr intermittent performance problems as well as hard starts, but only when cold outside?

 

FWIW I did the upgrade to MFI last year. In my case I had a misfire towing my fishing boat up a hill on #5 & found the pressure regulator wasn't holding pressure, but outside of the hill issue with a load, it ran and started OK. When I looked at the parts cost it was easy to decide to do the MFI upgrade as the PR comes with the new assembly. Pretty easy job and runs well since the upgrade with no misfire (I chose to go with a new Delco unit).

Why only a cold start issue I'm not sure, but a pressure drop that fast on shutdown points right at a PR (pr several leaking poppet valves) & that can definitely lead to hard starts.

The running pressures you posted look good, so that doesn't look like a fuel pump or blockage issue.

Water in fuel or other fuel issue would prob appear on more than cold starts as well & nothing about the pressure regulator should cause the stall/no start at the light you describes, so that is an unknown.....

If clutching at straws, there is a chance you have an electrical issue on the fuel pump circuit (separate from the pressure drop that can't be explained by an electrical issue). Could be a bad ground or connector issue to the pump. I got looking at the wiring when I replaced the fuel pump several years ago and re-did all the grounds at the time. Memory is bad, but it seems to me the fuel pump uses a chassis ground that is pretty exposed. However, I think all grounds are shared by other ccts, so any ground issue should show up affecting other things. Another possibility is If there is lots of crud on top of the tank, it is possible there is an issue there in the wiring or the connector - is the fuel gauge working OK??

 

Actually, my fuel guageis not working good, I thought it was bad guage, but thinking of it I have had a couple of electrical issues that could be a ground problem, mainly with rear tail lights. Will have to take a closer look into that tomorrow. Am going to pull spider in am, actually am going to pull upper plenum, hook fuel lines back up and run fuel pump and look for leaks before I remove, will pull all pipers and lay in tray to look for leaks there to. Then remove and go over before deciding on just replacing pr or upgrading to mpi.

 

Here is a grate video on testing your fuel system. About 1/2 way through, he tells you how to jump the relay pins in the fuse box, to make the fuel pump run without the relay plugged in for testing. With the fuel pump on, you can look for leaks in the system without the engine running. This will let you look inside the intake and be sure there are no leaks in the poppet hoses or any where else in the system. I pulled my throttle body and looked in my intake on my 97 5.7L, with a mirror and a flash light. I was able to see everything with the mirror, shining the flash light into the mirror once I put the mirror in the hole where the throttle body was.

 

Here is a grate video on testing your fuel system. About 1/2 way through, he tells you how to jump the relay pins in the fuse box, to make the fuel pump run without the relay plugged in for testing. With the fuel pump on, you can look for leaks in the system without the engine running. This will let you look inside the intake and be sure there are no leaks in the poppet hoses or any where else in the system. I pulled my throttle body and looked in my intake on my 97 5.7L, with a mirror and a flash light. I was able to see everything with the mirror, shining the flash light into the mirror once I put the mirror in the hole where the throttle body was.

 

Hey thanks, like I said ( I think ) in first post I did a load test on and wave test on fuel pump. Was pulling 10.3 amps with a 6000+rpm. Rating for new pump is 6000 rpm for that 5.7 vortex suburban 4 wheel drive. I 2 years ago rebuilt motor and reused old spider, ( I know mistake) had a couple poppers and hoses that were suspect when I reinstalled, hade to open back up and replace, mime is the csfi which you can replace parts on unlike the csfi which can't be repaired. Any way just upgraded to mpi, old spider had all kinds of issues. But planned on the upgrade and bought everything before starting. Truck starts right up, I know fuel pump is pumping 62psi on cold start, had purl pressure tester hooked up before attempting startup where I could see from cab. Had only 32psi, don't know how truck started but it did, walked around to side of motor compartment and what looked like the full 62psi was spraying out the flare fitting disconnect on rear of motor. I am an old motor head, my father thought me how to build racing motors before I could drive and I made my own fuel lines and brake lines, so I have everything and realize I probably cross threaded flare. Hers hoping not though.

 

Would like to thank everyone for viewing/responding to my post. Hot my fuel leak fixed (didn't have flare fitting set completely) finished mpi, filled a couple other things I found also. Truck starts right up and runs great. Fuel pressure still drops to 20psi when I cut off. And when I turn on pressure will jump to 60psi then drop to 20psi, when i crank it jumps back to 60, starts then drops to 52psi at idle. Left truck running an inspected fuell line from No i block to gas tank. No leak any where, I have camera I used to check on top of tank.
Have decide it just likes that pressure, though suspect check valve in fuel pump is at fault. I have a full 42gallon tank on this truck so I am going to buy a new pump and strainer sock and drive the gas out before truly deciding (though probably will let it ride) to drop tank.

 

Like you, my truck runs grate, but my fuel pressure drops off once I kill the engine. Its been that way for a long time. My truck just runs to good to fool with.