2003 Yukon xl low fuel pressure.

[Joseph Garcia]

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?

You've been asked a couple of times now to perform a specific sequence of fuel trim measurements and report back with you findings.

I suggest that you do that and let us know what you find out.

 

[Plattapuss]

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.

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

Sorry ltft

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

Not in the last 12 years I have had it. I did the carb spray thing didn’t detect anything. I didn’t think that could cause low fuel pressure anyway. Thank you

You've been asked a couple of times now to perform a specific sequence of fuel trim measurements and report back with you findings.

I suggest that you do that and let us know what you find out.

I will do that I have done so many things disconnecting the negative on the battery that maybe computer hasn’t setteled. How can you diagnose low fuel pressure pressure by the trims?

 

[Fless]

Are you sure that your fuel pressure gauge is accurate? Just askin'. Ever compared it with one that is rented from the auto parts store?

Circling back to the original problem: what symptoms/issues are you having that seem to be caused by low fuel pressure, or is this a case of "it measures low, so something is wrong?"

 

[Plattapuss]

Are you sure that your fuel pressure gauge is accurate? Just askin'. Ever compared it with one that is rented from the auto parts store?

Circling back to the original problem: what symptoms/issues are you having that seem to be caused by low fuel pressure, or is this a case of "it measures low, so something is wrong?"

I’m pre

Are you sure that your fuel pressure gauge is accurate? Just askin'. Ever compared it with one that is rented from the auto parts store?

Circling back to the original problem: what symptoms/issues are you having that seem to be caused by low fuel pressure, or is this a case of "it measures low, so something is wrong?"

im pretty sure my gauge is accurate even though it is a harbor freight. I got a loaner fuel gauge kit from auto zone so I could check the pressure at the fuel filter. Both gauges read the same
The car runs great, starts instantly, decent fuel mileage.
This started with a lean code po171. I wasn’t to savvy at using the reader but I think I saw both banks ltft at 23 on the freeze frame. Im giving up for now. Leaving on a 2000mi road trip towing a trailer tomorrow.

 

[West 1]

Running an engine lean causes excess heat in the combustion chambers. Running lean and towing? Not a good idea, you might melt a piston.

 

[strutaeng]

Running an engine lean causes excess heat in the combustion chambers. Running lean and towing? Not a good idea, you might melt a piston.

Agree 100%.

As far as I know, the ECU can correct up to +/- 25% percent on the fuel trims. Which explains why OP says truck runs good. But never wondered if that's still true under heavy engine load? IDK.

I would still recommend getting it fixed before towing long distances for sure.

Hopefully everything goes well and OP figures it out. Interested in the outcome...

 

[West 1]

If you notice the engine is laying down, by that I mean you are giving it more gas but it does not accelerate normally that is the first sign of lean burn detonation. You can save it by getting off the gas and letting the chambers cool.

Hope this is not your issue as it can be fatal but be aware on your trip so you get home in good condition.

 

[houstontaylor]

My 2003 flex fuel Tahoe has fuel pressures in the 40s also but has no fuel trim problems now. I was getting air leaks around the manifold absolute pressure sensor on top of the manifold due to a worn rubber seal. Also, I had replaced the injectors thinking they might have had a problem and did not lubricate the holes they go into when reinstalling them, damaging the O-rings or maybe they were damaged due to vibration and no lubrication. I found the leaks around the injectors with a smoke test. Anyway, replacing the injector o-rings and lubricating the holes before reinstalling them eliminated that major air leak. Good luck.

 

[Plattapuss]

Agree 100%.

As far as I know, the ECU can correct up to +/- 25% percent on the fuel trims. Which explains why OP says truck runs good. But never wondered if that's still true under heavy engine load? IDK.

I would still recommend getting it fixed before towing long distances for sure.

Hopefully everything goes well and OP figures it out. Interested in the outcome...

 

[Plattapuss]

I completed 1,000 miles of my planned 2,000 mile trip from Idaho to San Diego. Lots of long grades to 6600 feet. Yukon and trailer were pretty loaded. She ran great the whole way. Dash fuel mileage average read 12 mpg in tow haul mode. I found some Ai information just today that my fuel pressure can be average for Yukons this year. I will try to attach a screenshot of Ai quote. Thanks!

 

[Matthew Jeschke]

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?

Bit confused by your post, I think you're saying you have a return style non-flex fuel motor you installed a flex fuel regulator on?

I've extensive experience with the fuel system.

You can run either the flex fuel or regular regulators in your system. The fitment is the same. However, you'll always see trims in neighborhood of +15% if you run flex regulator in non-flex motor because it decreases your fuel flow.

No need to dead head the pump,

Both flex and non-flex pumps are very similar.

If you get 48 KOEO then you have a Flex regulator which spec is anywhere between 48 to 54 PSI (I only ever got 48 with flex regulator)... for a non flex vehicle it's 58 to 62PSI.

The bleeping parts catalogs don't distinguish between flex and non flex regulators. SOME have a marking on them that say 4 bar (non flex 58PSI) and 3bar (flex 48PSI) which you maybe able to see in the photos.

There is a direct relationship between fuel trims and your rail pressure because as pressure decreases flow does as well. In short, the injectors have to open longer at a lower pressure, giving you POSATIVE trims.

The DTC doesn't trip till long term fuel trims exceed +/- 25%

The regulator drops rail pressure to maintain the same pressure from intake manifold to fuel rail. Otherwise, without a regulated fuel pressure the manifold vacuum would pull extra fuel out of the injectors and your fuel would never meter correctly. The return-less system uses manifold pressure sensor (vacuum reading) to adjust injector pulse width thus no need for a return style regulator. I kind of prefer return style but I digress...

Sounds like your truck is working fine. You just have the wrong spec regulator. Hope that helps.