Low Fuel Pressure & Not Holding Pressure

[20streetrod06]

my truck was sputtering as i drove home a couple days ago. and threw lean codes for bank 1 and 2, as well as an evap code. ( P0171, P0174, and P0449 respectively).

i checked fuel pressure, the book says 55-62psi, after cycling they key several times to try and build pressure, it only ever made it to 30psi, and would immediately start dropping pressure down to about 18psi, then would continue slowly bleeding down after that.

there are no odors of fuel and no visual leak, so i dont think a line has failed, but i have had pumps fail in the past, where it would pull fuel from the bottom of the tank, but a line was broke at the top of the tank so it would just splash back down into the tank.

My question is, if the fuel pressure regulator has gone bad, would it let fuel pressure constantly back to the tank, instead of building up to the ~60psi? of when they fail do they fail closed, and the symptom would be too much pressure at the test port?

 

[20streetrod06]

Edited title and first post after checking fuel pressure.

 

[EXT4ME]

Shortly after buying my 2003 Avalanche back in early 2020, it began having an issue of not starting immediately at first turn of the key.

If I turned the key on and gave it a few seconds, the engine would start and run just fine.

But, if I tried to quick start the engine after sitting for a bit, it would just crank over for several seconds before finally starting and running.

Checking the fuel pressure, I found the pressure would go up and maintain the full 50-60 PSI while the engine was running, but would slowly bleed off to zero when the key was turned off.

Since the fuel pressure regulator on my 2003 is located up on the driver's side fuel rail (later models have the regulator as part of the fuel pump inside the fuel tank) and it was fairly cheap, I bought and installed a new one.

No change.

What I came to understand was there is a check valve that is part of the fuel pump that is supposed to maintain the full fuel pressure long after the fuel pump is shut down.

The purpose of that is to provide the fuel injectors enough fuel pressure to function properly, even long after the fuel pump is turned off.

A properly functioning check valve should hold the full fuel pressure for practically forever as long as nothing else in the fuel system is leaking fuel.

I can go start the engine in my 2004 EXT quickly at first turn of the key even after that truck has sat unused for months on end.

Odds are, your check valve has also seen better days.

When you decide to change out that old fuel pump, make sure you use only an OEM replacement pump.

When I changed out mine, the starting issue went totally away and the fuel pressure stays at full all of the time.

 

[20streetrod06]

thanks! i assumed the pump, or a component of it was more than likely the culprit, as opposed to the regulator.

not sure why it would be throwing the evap code though.

 

[EXT4ME]

thanks! i assumed the pump, or a component of it was more than likely the culprit, as opposed to the regulator.

not sure why it would be throwing the evap code though.

What is the rust situation with your truck?

If you live in a rust zone, the top of the fuel pumps and the associated fuel lines are well known for rusting and causing any number of problems.

Any rust that would compromise the integrity of the fuel or fuel vapor system, could be a reason for an EVAP error code being thrown.

 

[20streetrod06]

the lines look bad enough that I don't trust them to not break while disconnecting, so I plan on ordering a set of them the same time I order a pump.

is the purge valve on the intake supposed to wiggle? it has always moved around, but normally doesn't have any evap codes.

 

[EXT4ME]

The valve will wiggle a little bit.

If I remember right, there is an o-ring that seals it.

If you suspect it of leaking air, spray around it with either some carb cleaner or brake cleaner while the engine is running.

Listen.

It might be time for a smoke test.

 

[20streetrod06]

ill check it for leaks this evening.

 

[20streetrod06]

no vac leaks at the purge valve.

fuel pump, fuel filter, and full set of fuel lines are ordered.

 

[WrenchIt]

I have this same issue (‘03, 2500). Some research indicated the slow start may be a crankshaft position sensor, but this thread seems more like the problem I’m having. Did the new pump / check valve solve the issue? Thanks for posting.

 

[20streetrod06]

I ended up replacing the fuel pump, fuel filter, and put all new fuel lines in it, as the originals were super rusted and brittle. I have had zero problems with it since.

I honestly think a good bit of my issue was a very clogged fuel filter. Before I dropped the tank, I disconnected the fuel supply line under the hood and jumpered the fuel pump relay to drain as much of the fuel tank as I could. When that was done and I went to disconnect the fuel filter, it sprayed fuel with quite a bit of pressure, when that line had been open to air on the other end for several minutes. But regardless, a clogged fuel pump wouldn't have caused my pressure to not hold when checking it at the test port.

I'm glad I dropped the tank and got to clean everything up on the tank, and new pump and fuel lines provide peace of mind for the long term!

Side note, mine never seemed to be slow to start. The crank position sensor is a cheaper option to try if your research has indicated it as a possible culprit.