2003 Yukon xl low fuel pressure.

[Plattapuss]

My 03 Yukon xl has low fuel pressure 48 koeo 48 running 42. I have tried everything . The vin is not flex fuel . It uses a fuel rail with the flex style regulator. It has a return at the pump. Everything I see for my year is a returnless pump with return line. I have managed to get a new pump and fpr . New filter, pump regulator. Cleaned grounds, checked voltage . It runs great. High fuel trims. Any ideas?Did a previous owner Chang parts? Motor?

 

[Miami-Dade]

@Plattapuss Moved you here from 2021+section. Welcome from cold NYC!

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally assist you with your issue, but other members of this Forum much more knowledgeable than me in this area will chime in.

 

[S33k3r]

This is not something I experienced myself, but from reading a bunch of forums and from threads in this forum, here are some things for you to consider:

1. Take a look at your fuel ventilation system. If the system isn't properly venting, you could have a partial vacuum fighting the pump. I'd especially look at the vent solenoid in the engine compartment. But you should check ALL of the venting system. Have you ever had trouble fully filling the tank?

2. Check your positive wiring, especially between the alternator and the power distribution block (the place where all the relays and fuses live, under the hood). You have not provided any other symptoms, so this is a long shot.

3. Wiggle all your grounds. Something could be loose!

4. Unfortunately, new parts are not all equal. Did you get an AC Delco fuel pump? A lot of us on this forum are skin flints and wouldn't spend a found penny if there were any other way. The recommendations across all forums I've read has been to go with the AC Delco pump. Barring that, there are several, reputable aftermarket vendors that provide performance pumps for out trucks. Unless you are running a modified engine -- or plan to! -- a performance pump is overkill.

Finally, where are you testing the PSI/How are you testing the PSI?

Good luck. Crap like this is annoying. The big stuff will make or break you, but the little stuff destroys sanity!

 

[SpareParts]

I assume you mean high as in high + fuel trims.

 

[SpareParts]

Also what are the LTFT?
EGR valve working?
Are the 02 sensors working properly?
What fuel pressure if you dead head the pump?

 

[Plattapuss]

This is not something I experienced myself, but from reading a bunch of forums and from threads in this forum, here are some things for you to consider:

1. Take a look at your fuel ventilation system. If the system isn't properly venting, you could have a partial vacuum fighting the pump. I'd especially look at the vent solenoid in the engine compartment. But you should check ALL of the venting system. Have you ever had trouble fully filling the tank?

2. Check your positive wiring, especially between the alternator and the power distribution block (the place where all the relays and fuses live, under the hood). You have not provided any other symptoms, so this is a long shot.

3. Wiggle all your grounds. Something could be loose!

4. Unfortunately, new parts are not all equal. Did you get an AC Delco fuel pump? A lot of us on this forum are skin flints and wouldn't spend a found penny if there were any other way. The recommendations across all forums I've read has been to go with the AC Delco pump. Barring that, there are several, reputable aftermarket vendors that provide performance pumps for out trucks. Unless you are running a modified engine -- or plan to! -- a performance pump is overkill.

Finally, where are you testing the PSI/How are you testing the PSI?

Good luck. Crap like this is annoying. The big stuff will make or break you, but the little stuff destroys sanity!

Great reply. Thank you. My last fuel pump replacement was an auto zone Delphi 6 years later I warranty replaced it. No change in fuel pressure. Not wanting to risk it I tried another cheap pump (precision) I have done the fpr, new filter, maf, o2 sensors. Cleaned throttle, checked voltage at pump, cleaned grounds. The car runs perfect lots of power and decent fuel mileage. Luckily 6 years ago I cut an access hole to the pump. Makes for easy replacement and testing. I am certainly no automotive diagnoses guy just a diyer. No trouble with fueling. High fuel trims in the 11 to 14 range.

 

[Fless]

Which engine?
Is the XL a 1500 or a 2500? Some of the 2500s take a three-hose fuel pump.

I'd like to see more detail on the short- and long-term fuel trims. What are they at hot idle, and at 1800 rpm or so? (8 numbers total)

 

[Plattapuss]

Also what are the LTFT?
EGR valve working?
Are the 02 sensors working properly?
What fuel pressure if you dead head the pump?

Ltft are in the 12-14. New oxygen sensors no changes. Haven’t checked egr valve but will do. Looking into how to dead head the pump but I have tried 3 different pumps. Thank you for your reply.

 

[strutaeng]

Low fuel pressure but high fuel trims doesn't make any sense to me.

Post the fuel trims as mentioned above...

Low fuel delivery will typically cause a lean on both banks, almost exactly the samd percentage.

Were the injectors replaced at any point before? Different injector flowrates will cause the wrong amount of fuel injected into cylinders, and your fuel trims will reflect this.

What is the history with the truck? You just bought it? Sounds like you've had it 6 years? I'm assuming it was running good before? Did you change anything prior to having the issue?

As far as low fuel pressure, it can only bf the fpr or fuel pump itself, unless you have an external leak somewhere.

 

[Plattapuss]

Which engine?
Is the XL a 1500 or a 2500? Some of the 2500s take a three-hose fuel pump.

I'd like to see more detail on the short- and long-term fuel trims. What are they at hot idle, and at 1800 rpm or so? (8 numbers total)

It’s the 1500 gas. 2 fuel lines at the pump I don’t. Ltft can be in 11-14 occasionally a little higher at higher rpm then sometimes when driving when I slow down they can go down around 9. Thanks

 

[SpareParts]

Im thinking a vacuum leak.

 

[Plattapuss]

Low fuel pressure but high fuel trims doesn't make any sense to me.

Post the fuel trims as mentioned above...

Low fuel delivery will typically cause a lean on both banks, almost exactly the samd percentage.

Were the injectors replaced at any point before? Different injector flowrates will cause the wrong amount of fuel injected into cylinders, and your fuel trims will reflect this.

What is the history with the truck? You just bought it? Sounds like you've had it 6 years? I'm assuming it was running good before? Did you change anything prior to having the issue?

As far as low fuel pressure, it can only bf the fpr or fuel pump itself, unless you have an external leak somewhere.

No detectable fuel leaks. I have had the car for 12 years . Has 215 miles. Starts instantly runs very good. I can reset fuel averages and get 13 the cararound town 16 freeway. Starting to think it ha run this way since I have had it. Fuel trims up and down probably average 11-14. Changed all components fpr 3 times 2 pumps, filter maf, checked pressure at filter, cleaned grounds. Checked voltage at pump 14 plus running. Thanks for your input.

 

[Plattapuss]

It’s the 1500 gas. 2 fuel lines at the pump I don’t. Ltft can be in 11-14 occasionally a little higher at higher rpm then sometimes when driving when I slow down they can go down around 9. Thanks

5.3 gas

 

[Fless]

Im thinking a vacuum leak.

So am I, but without specific fuel trims at the two rpms, and maybe some additional info, there's no way to do more than guess.

SWAG: MAF mis-reporting? Aftermarket or dirty MAF? Intake leak between MAF and throttle body? I could go on and on.

I'm not sure why you'd have trouble finding a fuel pump with two fuel line connections at the pump -- pretty much all of them on Rock Auto are that way. Unless, of course, I'm misunderstanding and that's not what you have. Write full sentences so this feeble mind can comprehend.

 

[Plattapuss]

Which engine?
Is the XL a 1500 or a 2500? Some of the 2500s take a three-hose fuel pump.

I'd like to see more detail on the short- and long-term fuel trims. What are they at hot idle, and at 1800 rpm or so? (8 numbers total)

Xl 1500 5.3 t vin. 11-14 hot idle short term always jumping around hard for me say -up to 6 jumps around a lot . I see a lot of plus 3 sometimes higher. Cruising can be a bit higher but will drop down into the - 10 fange. Thanks

 

[Plattapuss]

So am I, but without specific fuel trims at the two rpms, and maybe some additional info, there's no way to do more than guess.

SWAG: MAF mis-reporting? Aftermarket or dirty MAF? Intake leak between MAF and throttle body? I could go on and on.

I'm not sure why you'd have trouble finding a fuel pump with two fuel line connections at the pump -- pretty much all of them on Rock Auto are that way. Unless, of course, I'm misunderstanding and that's not what you have. Write full sentences so this feeble mind can comprehend.

lol I’m a bit feeble minded myself. Sorry I can’t be not clear on fuel trims as they are always all over the place . I figured it was related to the low pressure. Interesting you mentioned throttle body because this all started a short time after I removed the throttle body with a po171 code. One of the first things I did was to check I had tightened it properly. Then I removed it to check the gasket. Either there was not one there or it was stuck to engine. I saw a blue rubber thin all around in good shape so I figured that was the seal. My thoughts were that couldn’t cause low fuel pressure anyway. Thanks again.

 

[strutaeng]

Ok, so i missed tbe fuel trims you mentioned earlier. That seems a bit on the lean side. I think something like a constant 12 percent will trigger the lean code...

Vacuum leak test:

1. monitor the fuel trims at idle: report the values for each bank, both short and long terms.
2. Do the same for 2,000 rpm
3. Do the same for 3,000 rpm.

Report findings.
A. If fuel trims IMPROVE (or get closer to zero) with rpm increase, then very possible vacuum leak.
B. If fuel trims get worse, likely fuel delivery issues.

 

[SpareParts]

Has the intake manifold gaskets ever been changed?
I have had both high + and high - fuel trims caused by vacuum leaks on various areas.

 

[West 1]

Any chance you have an exhaust air leak before the first O2 sensor drawing in extra oxygen.

Run a smoke test in the intake and watch for a smoke leak. That will rule out any intake or evap issues. I do smoke checks with about 3 psi pushing smoke filled air into the intake. Sometimes it finds problems that I could not find. One car it was the EVAP cannister at the rear next to the gas tank, The Evap cannister itself was leaking around the upper and lower half. If smoke comes out, air leaks in when the engine is running.