fuel pressure regulator

Hi,
My truck (97 K1500 5.7) is losing fuel pressure quite fast after turning off the key.
62 lbs while the pump is running, but it drops to 20 in a few seconds after the pump is off.
If I clamp the return line, the pressure goes up to 80 but still drops to 20 or less when the pump is off.
The shop manual is a bit confusing in the diagnostic flow chart.
What is a good way to decide if it is the fuel pressure regulator or the fuel pump check valve?
The fuel pump is only 5-6 months old, Delphi brand.
Thanks,
Bob B

I forgot to mention that the reason I looked at the fuel pressure was,
When I started it, it stalled when I put it in gear. I restarted it and it drove and stalled all the way into my workshop.
While it is running the pressure is down maybe to 50.
I'm leaning toward the regulator at this time.
BTW, 133,000 miles on it.
BoB B

have you checked or replaced the fuel filter in a while ?? (just giving you an idea before you pull the pump again) !!

have you checked or replaced the fuel filter in a while ?? (just giving you an idea before you pull the pump again) !!
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Yes I replaced it yesterday.
Read my new post about fuel pump pressure.
Bob B

To check for fuel pump leak back as soon as the fuel pressure is up pinch off the pressure feed line between the gauge and the fuel pump.
Fuel pump check valve causes leak down after shut off.
The 50 running is kinda low.
Specs are 60/66 CSI and 56/62 for SFI
Make sure pump is not fading out on hot run.
Hook it up gauge and tie it to mirrow or tape to windshield and check running down the road pressure.
Mt-2500

[QUOTE=MT-2500]To check for fuel pump leak back as soon as the fuel pressure is up pinch off the pressure feed line between the gauge and the fuel pump.
Fuel pump check valve causes leak down after shut off.
The 50 running is kinda low.
Specs are 60/66 CSI and 56/62 for SFI
Make sure pump is not fading out on hot run.
Hook it up gauge and tie it to mirrow or tape to windshield and check running down the road pressure.
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I did the pinch the lines diagnostic and got a bit confused by the results.
It leaked down with both lines clamped.
I intend to re do that again this morning, It's possible my clamp didn't close the line completely.
BTW I can't drive it this way cause it will stall too much.
Bob B

If it is leaking off with both lines pinched,you need the check fuel pressure reg and lines inside plamtuim.
When you have plamtuim off turn key on and watch for leak down or fuel leaking out in there.
MT-2500

[QUOTE=MT-2500]If it is leaking off with both lines pinched,you need the check fuel pressure reg and lines inside plamtuim.
When you have plamtuim off turn key on and watch for leak down or fuel leaking out in there.
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I replaced the regulator last night and same problem, I can't see any fuel leaking inside the plenum area. No place else for the gas to go but the injectors, but no black smoke or other flooding symptoms.
I will recheck making sure the clamping is really sealing the lines today.
If nothing changes, I guess I'll have to remove the injectors and meter body to have a look.
I could lift the injectors and see if any are leaking. But I'm proceeding cautiously because it is new territory.
I'm almost hoping that pinching the hoses (better?) will point to the fuel pump. Even though that is a big nuisance job, The pump is still under warrantee until feb.
I think I might cut a flap in the bed this time if I go there.
Bob B

To check the injectors for leak down.
Find a shop with a engine capable scanner that can run a injector balance test.
Is the fuel pump lossing pressure after it warms up.
Also check voltage and wiring running to pump.
Check engine running pressure after it warms up and also on he road.
Good Luck
MT-2500

OK I made a mistake when going down the diagnostic chart.
Turns out it now blames the 6 month old fuel pump.
So I added my own test: i pulled the fuel lines from the injector block and put a piece of hose on the supply line from the tank and clamped it off. The symptoms are the same, good pressure with power on the pump
and when I cut off the power, the pressure drops fairly fast.
So with just the fuel line and the pressure gauge involved. it has to be the pump.
NAPA has ordered the Warrantee replacement pump for tomorrow.
Thanks all for the helpful ideas.
Ready to drop the tank this time because it only has 1/4 full.
I will cut a flap in the bed when the tank is out (for next time), because the saw blade would hit the tank and lines with it in place.
Bob B

Good luck and let us know how it goes.
MT-2500

From my understanding, a fuel pump regulator on these trucks will either work or not work. Is that not true?

If The fuel pressure regulator is bad they will do several things .
Like leak off fuel pressure and sometimes they do not hold the right pressure. To much or not enough.
MT-2500

Good luck and let us know how it goes.
MT-2500
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I will definitely give feedback, thanks.
See my post about the bed cutout where I try to explain or justify cutting the bed opening.
BTW there were others on this site that are for cutting it. Also the pre 1990 Range Rovers, the dealers have a template to show where to cut the floor.

Bob B

OK I replaced the fuel pump yesterday and it fixed the pressure drop problem. Now to tackle the coolant drip from the intake manifold.
And since I replaced the pressure regulator in the start of this when I took a wrong turn during diagnostics, I left the new one in.
I did do the cutout in the bed so if it dies again while on the road (twice), I can get to it. Next to find a damaged bed in a wrecking yard so I can make a good looking cover. It will be covered most of the time by the tool box anyhow.
Bob B