Stumped...low fuel pressure when engine was hot.

[Blueduck]

Looking for some help with a strange issue with 1997 gmc Sierra c2500 2wd with a 5.7
Drove into town yesterday evening..truck started and ran fine. Turned it off went into store came out cranked it and it fired and ran for about 2 seconds then died. After that I had a no start issue while in the parking lot. Had to get towed home. Once home (about hour later) I hook up my fuel pressure gauge and key on primes at 62 psi. 60 psi after prime. Holds fine. I cranked her over and she fired right up but fuel pressure instantly dropped from around 55 to 10 in around 12 seconds resulting in the engine dying. I reproduced this several times last night. Checked for fuel leaks found none. Figured pressure regulator took a crap. Went to work today...got home Went to the shop and truck fires right up. Over and over again. I check pressure. 62 psi while priming. 60 psi key on engine off. 56 psi at idle. Hits 62 psi instantly with blip of throttle. Drove it around the property..got it up to Temps. I cannot reproduce the symptoms I had yesterday. I'm stumped.
No CEL
New Delphi fuel pump installed 14 months ago along with new fuel filter and pressure regulator. (Went bad)
Upgraded spider injection installed by shop around 4 years ago by previous owner (my father) when I was changing out the pressure regulator I checked the numbers on the spider unit and unfortunately it's a cheap ebay unit. I really wanted to change it out but couldn't find a Delco or Delphi unit in stock Anywhere!
Any advise/ideas on what's going on is much appreciated. Thanks in advance!

 

[Schurkey]

Intermittent fuel pump--faulty pump, maybe faulty wiring?

 

[DonYukon]

So I had a similar issue first intermittent and it got worse until the truck would do it every time i tried to drive it. Turned out mine was a coolant temp sensor reading extremely hot/cold at random intervals during its operation. causing it to stall and not to idle properly would have hard starts sometimes and others not and once running it would stall in gear. turns out the sensor was telling the ECU it was too hot/cold . i spent hours chasing fuel pressure and what i thought was delivery problems. new sensor fixed it right away. if you got a scan tool check what temps its relaying to the ECU. if not a temp sensor is a relatively cheap part to shotgun at it lol . even though I hate shotguning parts but worth a try.

 

[RanchWelder]

What he said ^^^...

The stock pump has a back flow ball internally.
If the rubber hose is deteriorating or has internal debris, the back flow valve could be compromised, once the computer cycles the pump, under driving conditions.

I have read forum members claim the brand new pump out of the box had bad check ball valve seal.

Did you swap the rubber hose at the new pump with a new one or use the old one?
Did you swap the stupid squeeze clamps out for better crimp clamps or use the old ones?

Did you accidentally install the fuel filter backwards? (Don't laugh, I have done this too).

Check your o-rings at every fuel fitting everywhere and change them all.
Then you can be certain a $5.25 two o-ring set, is not the issue.
They run that much for 2.

You may find them "square", crushed, broken and missing, at the fuel tank and every quick connect fitting along your entire fuel line system.

It is not uncommon to overlook a stain of dried fuel on top of the tank too.
I had green a/c o-rings installed by someone else, on my used Blazer.
They were slightly leaking at the tank... the fuel stain was there, why did I ignore it, when I replaced my pump? IDK... I thought the green o-rings were correct?
Not.

The reliability and quality of the fuel pumps and regulators is very concerning...

My 4.3L spider had to be replaced 3 times in 4 years because the seasonal fuel additives from the gas station, were causing a rust like buildup behind the filtration screens at the under plenum at the pump and clogging the injectors, contaminating the FPR or blocking fuel flow and showing pressure variations.

This brown crud would "grow" behind the filter screens. Back then, the nut set was $350 and only available from the dealership. I bought three of them.
You said you have no idiot lights, so hopefully, this issue is not your problem.
Just be aware, clogged spider screens is an issue. This crap can clog up the FPR under the plenum as well.

If your spider filters are clean, your o-rings are all fresh nitrile OEM quality and the FPR is replaced with a quality unit, you might want to call a hot rod parts supplier and invest in a high quality aftermarket pump.
The crap off the shelf has been declining rapidly the past few years.
Name brands used to be the best solution... not so much anymore.
The internal styrene plastic these pumps are being made from can be very low quality and from poor plastic castings.

If you go lean under hard acceleration (or ignore the problem), you'll be building a new engine. Once detonation starts, the computer will keep adjusting until you fall off the scale and fuel economy and engine wear may both occur.

Good luck.

 

[Blueduck]

What he said ^^^...

The stock pump has a back flow ball internally.
If the rubber hose is deteriorating or has internal debris, the back flow valve could be compromised, once the computer cycles the pump, under driving conditions.

I have read forum members claim the brand new pump out of the box had bad check ball valve seal.

Did you swap the rubber hose at the new pump with a new one or use the old one?
Did you swap the stupid squeeze clamps out for better crimp clamps or use the old ones?

Did you accidentally install the fuel filter backwards? (Don't laugh, I have done this too).

Check your o-rings at every fuel fitting everywhere and change them all.
Then you can be certain a $5.25 two o-ring set, is not the issue.
They run that much for 2.

You may find them "square", crushed, broken and missing, at the fuel tank and every quick connect fitting along your entire fuel line system.

It is not uncommon to overlook a stain of dried fuel on top of the tank too.
I had green a/c o-rings installed by someone else, on my used Blazer.
They were slightly leaking at the tank... the fuel stain was there, why did I ignore it, when I replaced my pump? IDK... I thought the green o-rings were correct?
Not.

The reliability and quality of the fuel pumps and regulators is very concerning...

My 4.3L spider had to be replaced 3 times in 4 years because the seasonal fuel additives from the gas station, were causing a rust like buildup behind the filtration screens at the under plenum at the pump and clogging the injectors, contaminating the FPR or blocking fuel flow and showing pressure variations.

This brown crud would "grow" behind the filter screens. Back then, the nut set was $350 and only available from the dealership. I bought three of them.
You said you have no idiot lights, so hopefully, this issue is not your problem.
Just be aware, clogged spider screens is an issue. This crap can clog up the FPR under the plenum as well.

If your spider filters are clean, your o-rings are all fresh nitrile OEM quality and the FPR is replaced with a quality unit, you might want to call a hot rod parts supplier and invest in a high quality aftermarket pump.
The crap off the shelf has been declining rapidly the past few years.
Name brands used to be the best solution... not so much anymore.
The internal styrene plastic these pumps are being made from can be very low quality and from poor plastic castings.

If you go lean under hard acceleration (or ignore the problem), you'll be building a new engine. Once detonation starts, the computer will keep adjusting until you fall off the scale and fuel economy and engine wear may both occur.

Good luck.

Thank you for the insight. The pump, filter and FPR were replaced 14 months ago. Everything was installed correctly. The truck has run perfectly since then until this situation. There was pressure loss when It acted up but the following day it runs perfectly again. That's what has me stumped.