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1997 Chevrolet K1500, 5.7 Fuel Delivery System. I have had

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1997 Chevrolet K1500, 5.7 Fuel...
1997 Chevrolet K1500, 5.7 Fuel Delivery System. I have had this truck for 400,000 miles and I know the truck owes me nothing but my truck does not start and continue to run. It will start if I spray Starting Fluid into the TBI but dies. During the PRIME Cycle, it goes to 62 psi but immediately go down to zero rather quickly. Normally within 2 seconds. I have replaced the Fuel Pressure Regulator twice, I have also replaced the Fuel Pump 7 times with DELPHI pumps. I have now installed a Used Spider Assembly from a running Tahoe with 70,000 miles.
Today, I unplugged the Fuel Pump and applied 12v direct to the pump and it goes up to 62 psi and 3 seconds later, it goes to 30 psi and you can hear the Fuel returning to the Fuel Tank. I know the poppets require 55 psi to function.
Why with the Fuel Pump running constantly, does it drop to 30psi and return the fuel back to the Tank. THREE Pressure Regulators have been installed and it is a no go.
A. What component keeps the Fuel Pressure UP after shutting off the Ignition
B. What is causing the Fuel Pressure to drop to 30 and fuel returning to the Tank
C. Why is the System not maintaining Pressure during the PRIME cycle?
D. Why will my truck not continue to run?
Submitted: 2 years ago.Category: Chevy
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Customer reply replied 2 years ago
I replaced the SOCK on the Pump every time. YES, I replaced the Fuel Filter Multiple times...
Customer reply replied 2 years ago
There was ZERO indication that the Fuel Pressure Regulator was leaking, I visually inspected the Upper Intake. Additionally, there is NO Fuel Leak when I visually inspected the lines from the Fuel Pump to the Fuel Rail Assembly....
Answered in 1 hour by:
11/28/2015
Chevy Mechanic: George H., ASE Certified Technician replied 2 years ago
George H.
George H., ASE Certified Technician
Category: Chevy
Satisfied Customers: 19,031
Experience: GM Tech ASE Master Tech 15+ years
Verified

Hello I will help you with your question,

You are replacing the whole pump module each time or just the pump motor?

Can you disconnect the return line at the filter area and cap the pipe from up front?

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Customer reply replied 2 years ago
I replaced the Pump Motor, not the Entire Assembly, I have Ohm'd the Wires as I know there is a known issue with Corrosion on the Connector on the Wire. I have Replaced the Pump to Assembly twice as I also know this to be a very common issue with the Fuel Pump Assemblies.For Clarification, I completely disconnected the Fuel Pump from the Wiring Harness, I have ran a 12v Hot Wire to the Fuel Pump directly to the Pump and although it does run the Pump, it drops pressure from 62 to 30 and you can hear the fuel being dumped back into the tank. I have also pinched off the Return line and pressure goes up to 75-80 psi and the needle moves from the back pressure.Question:
a. Why is the pressure dropping off as the Pump runs...
b. Why or What is suppose to keep the Pressure above when wired straight with no Cam Input?
c. I have replaced the 3 Pressure Regulators, Fuel Filters, Spider Assemblies, Fuel Pumps but it will not maintain Pressure and there is no visible leaks anywhere?
Chevy Mechanic: George H., ASE Certified Technician replied 2 years ago

OK, several questions to narrow this down,\

You pinch off the return and get full pressure?

You ran and 12 volt feed to the pump and the pressure drops off as it is running? Did you also run a ground?

How many O rings are on the regulator? Large and small?

Are you able to put the gauge on the end of the feed line from the pump? Maybe at the filter to block off the line and measure pressure? If you do that does the pressure hold?

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Customer reply replied 2 years ago
It is late at night but wanted to let you know that it is 10pm and will do this in the morning and report back.
a. Yes, I used my Vacuum Flat Clamp pliers to avoid damaging the hose and it kept running at 75psi.
b. Yes, I ran a 20' Power / Negative lead DIRECT from the 12v Main Battery to the Pump (Grey) and Black (Ground). The Pump ran continuously... Initial 62psi then dropped to 30psi and then you can hear the Fuel dumping into the Tank. At this point I have NOT pinched off the line with the Direct Power not ran through the vehicle bus... So Positive and Ground was ran.
c. There was one Large and one small at the bottom where it attaches to the Spider Assembly. Both are in place.
d. I can disconnect and put the gauge pre-injection assembly, this will take the Pressure Regulator and Spider Assembly out of play.FYI, I have been an ASE Mechanic since 1979, this one is just driving me up a wall and of course, it always takes the back burner to paying jobs..... Yes, it is my own personal truck, 400,000 miles and I have put 383,000 of them on myself.I will reply to you in the AM when the sun is out.
Chevy Mechanic: George H., ASE Certified Technician replied 2 years ago

I will be here most of the day tomorrow so let me know what you find.

Sounds like if you have the pump running with good power and ground and the pressure drops off then you have to look in the pump module.

Block off the line at the filter and put the gauge on it, I have a Motorvac machine that lets me do this but may pressure test kits do as well.

Maybe the check valve in the module is not holding, it is not in the pump motor. Let it build pressure and turn it off and see if it holds.

Next you say the pressure is good with the return pinched??? I thought it was a solid line but if it does then you have to question the regulator. You replaced it but was a small O ring left in the intake??

The way to find out is to split the system, give the pump good power and ground, split the system to see where it loses pressure and then we can work from there.

I will be here tomorrow so let me know what you find and how I can help

Thank you

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Customer reply replied 2 years ago
I am sorry that I was unable to get to test the Fuel Pressure at or before the Fuel Filter to isolate the Spider Assembly yesterday as I was quite sick from working in the Cold and I think it wise that I not attempt anything until tomorrow but I will do the test tomorrow morning before 10am EDT.I am still trying to understand my issue so please bear with me, can you answer the following for me?
a. If the Pressure Is Constant after capping off the Pressure Line to the Engine and the pressure is 62 psi. This would mean the pressure release is not associated with the Pump but a component Upstream. This goes back to my original question.
(Q1) What component maintains and releases the pressure in excess of 62 psi?b. If the Pressure is being released pre-Filter, this would indicate a leak or an issue with the pump. The problem with this is, I have released with 7 DELPHI pumps and no change.
(Q2) So the issue will be with the Pump Assembly (Module)c. When I pressurized the pump directly, the pumps holds @ 62 psi for a few seconds and then kicks down to 30 and then I can hear the Return Line dumping the fuel back into the Tank. I understand the Pressure Regulator works off the Increase Vacuum inside the Upper Intake Plenum This keeps bringing me back to the same question
(Q3) What Component Holds the Operating Pressuse @ 62 or more when increasing the RPM?It keeps coming back that there is either a component that is failing upsteam (Spider Assy, Fuel Pressure Regulator) but with me replacing the Pressure Regulator 3 times and using 2 separate Spider Assemblies (the one currently int he Truck came out of a Running Truck).... That I am missing something, another component or a leak I am not seeing or smelling....Your Thoughts before tomorrow's testing?
Chevy Mechanic: George H., ASE Certified Technician replied 2 years ago

Rest up, it is just a truck!

I am here most of the time so let me know what you find when you get a chance to check it.

If you can deadhead the pump and it holds pressure then it is not the check valve in the pump module. You say you are changing motors not the module, the check valve is in the module.

You also say that you can restrict the return line and the pressure comes up? It is the regulator's job to maintain that pressure. You changed it but did you leave an O ring behind so the new regulator is leaking pressure?

The easy way to check this is to walk through the system. See if the pump holds, if it does then block the return line and see if pressure holds. If it drops when you open the return line the problem is in the regulator or the fuel body.

Step by step eliminating each component as the cause is the key to finding out what is happening.

Once the pump makes pressure and you shut it off there is no electrical component to deal with.

Let me know what you find

Thanks

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