Need help narrowing down low fuel pressure...

[BOOM_FIST]

2003 Yukon XL 2500 6.0 - Just rolled 198k

Having a minor bump in idle with a slight intermittent straining/whining sound that sounds like it's coming from the fuel line. When I touch the FPR I can feel the vibration and hear the sound coinciding. I've done a slew of 'peace of mind' maintenance since I bought it back in Jan of this year.

AC Delco Fuel Pump
AC Delco Fuel Filter (twice for troubleshooting)
AC Delco FPR (twice for troubleshooting)
AC Delco spark plugs
MSD wires
1Aauto coil packs
AC Delco 145A alternator
AC Delco OPS
AC Delco water pump
AC Delco coolant cap
Stant Thermostat
Coolant Flush
Fel Pro intake gaskets
AC Delco knock sensors
Dorman knock sensor harness
MSD wires
1Aauto coil packs

NO codes, NO other issues besides the bumpy idle and the straining noise coming from the fuel line. Under WOT it feels fine, but not as strong as it should be...if that makes sense. Cruising speed is fine too.

Fuel Pressure reads 56 PSI, key on, engine off. 48 PSI, key on, engine on. Pressure holds at 55-56 PSI when shut off, so no suspicion of leaky injectors. While engine is running, removing the FPR vacuum line raises to 60-62 PSI, no fuel coming out of the new FPR.

I'm suspecting a bad New fuel pump or clogged fuel line somewhere in between the fuel pump and FPR?

Might be a weird question, but could a bad gas cap cause low fuel pressure? When I fill up at the gas station I don't hear any pressure relief when removing the gas cap...is that normal?

Thanks all,

-Tom

 

[BOOM_FIST]

Just replaced the gas cap yesterday in hopes of a dumb miracle fix......nope. I also disconnected the battery again to see if that would "reset" anything. I'm desperate and REALLY don't want to do another fuel pump. That might be the route I have to go though.

Any thoughts guys?

 

[swathdiver]

Hi Tom, do you have a good scan tool that can see all the fuel system parameters?

 

[BOOM_FIST]

Hi Tom, do you have a good scan tool that can see all the fuel system parameters?

Negative...my next step is to take it in somewhere to have a diagnostic check run. I'm about done fooling with this and taking random shots in the dark.

 

[afpj]

Because I'm a simpleton, I am going to suggest simple things, that a sophisticated lad like yourself might miss, and I didn't see it on the list...
Clean your MAF and TB. Make sure your engine air filter is clean

 

[BOOM_FIST]

Because I'm a simpleton, I am going to suggest simple things, that a sophisticated lad like yourself might miss, and I didn't see it on the list...
Clean your MAF and TB. Make sure your engine air filter is clean

Lol, sometimes it’s the little things that get us, but I forgot to mention I did those too. Sorry man, I appreciate your input!

 

[M1Gunner]

The Evap vent is normally open unless running an Evap monitor. So to answer your question, no you should not hear a difference in pressure hiss when you remove your fuel cap.

 

[M1Gunner]

If you have a gauge with a hose long enough, mount the fuel pressure gauge to the windshield. Make sure not to pinch the hose between the hood and cowl. Test drive and watch the fuel pressure in action to verify the pump can keep up with the demand.
Get a scan tool that will show fuel trims and monitor the short term fuel trims while conducting normal driving and WOT tests.

 

[M1Gunner]

Also what grade fuel do you use and any record of o2 sensor maintenance?

 

[swathdiver]

If the scan tool is good enough to see fuel trims, it should be good enough to read the commanded and actual fuel pressures, the manual gauge being redundant but still not a bad idea.

 

[BOOM_FIST]

Also what grade fuel do you use and any record of o2 sensor maintenance?

I just run regular ol’87. I tried 89 recently, but it made zero difference except made my wallet lighter.

If the scan tool is good enough to see fuel trims, it should be good enough to read the commanded and actual fuel pressures, the manual gauge being redundant but still not a bad idea.

That’s my next step then. I’m going to have a shop run it with a scan tool to log some real-time data. I’m suspecting a defective fuel pump or a blockage in the fuel line.

 

[swathdiver]

One tank isn't enough to tell, especially since it was just 89. 87 is really crap fuel, you'll gain at least 2 mpg and probably more by switching to 91/93 from a top tier station like Exxon/Mobil or Chevron. By the 3rd tank you'll see the full extent of the gains made and realize that in most cases, it costs more money to run cheap gas both in loss of efficiency, mpg, and in fuel system repairs like you're having now. That's been my experience for the last thirty plus years anyway.

 

[BOOM_FIST]

One tank isn't enough to tell, especially since it was just 89. 87 is really crap fuel, you'll gain at least 2 mpg and probably more by switching to 91/93 from a top tier station like Exxon/Mobil or Chevron. By the 3rd tank you'll see the full extent of the gains made and realize that in most cases, it costs more money to run cheap gas both in loss of efficiency, mpg, and in fuel system repairs like you're having now. That's been my experience for the last thirty plus years anyway.

Hmm, interesting. I guess I'm willing to try anything at this point. Lol. Thanks James!

 

[swathdiver]

Hmm, interesting. I guess I'm willing to try anything at this point. Lol. Thanks James!

I don't think switching to high test is going to solve this particular problem but stranger things have happened. If you get on it, go full throttle, does she fall on her face or keep pulling?

I reread your post about fuel pressures. I don't know much about mine either but the computer commands it and the pump delivers 43.5 psi all the time. Granted we have different engines but just saying. I see all this talk about my motor supposed to have 58 psi of fuel pressure too and it might be true with the key on and the engine off, but it's always been 43.5 psi.

 

[BOOM_FIST]

....If you get on it, go full throttle, does she fall on her face or keep pulling?

That's the weird part...she pulls hard as ever with no stumble or power decrease. It's just when sitting in Park and idling and when in Drive sitting at red lights. I'm going to try and take a good video of it to better explain my symptoms. Hearing the audible "strain/whine" sound is hard to explain.

 

[swathdiver]

And you said there was a vibration in synch with the strain/whine right? Maybe the mount for the pump is not as tight as it could be, something loose, maybe the pump bearings aren't the greatest. In my old Buick, when it was low on fuel the fuel pump was much louder as it was no longer submerged and muffled. So this happens with low and full tanks too then?

If you're getting low on fuel, put some high test in it and one or two of those little 6 oz bottles of Super-Tech from Walmart. I don't think the pump is bad in that its not performing as you have full power.

 

[BOOM_FIST]

I need to fill up today anyway, so I'll try that. Thanks man

 

[BOOM_FIST]

Filled up with 93 and added 2 different Fuel injector cleaners to this last tank. So far, nothing has changed.

I've been digging around online and saw that some 04+ 2500HD's came with a FPR similar to ours, but had a little T10H torx screw on the body of the regulator to adjust fuel pressure. I've been wondering if I could just source one of those and mess with my fuel pressure to see if that alleviates my symptoms???

Here's a pic of what I'm talking about...

 

[BOOM_FIST]

AHHH! I found a YouTube video of my EXACT same symptom. This is on a 5.3 Tahoe though...SKIP TO 0:30 to hear the sound.

It seems that people are reporting back with this symptom being AC Delco and Delphi brand related. The BWD brand from AutoZone/Advance Auto seem to work better for our trucks? Might give it a shot!

 

[swathdiver]

Now if you stick a long extension on the FPR and the other to your ear is that exactly where the sound is coming from? If so, then mystery solved!