99 Suburban Fuel Pressure Regulator Noise

I have a high pitched noise that is particularly noticeable in the cabin of the vehicle, almost like a vacuum whistling. It's quite noticeable at idle and seems to fade quickly with throttle, but returns at idle. Any heavy electrical load on the vehicle (like rolling down several windows simultaneously) also seems to drop the pitch of the noise. I have chased this thing for months, and I finally think I have zeroed in on it. When I put a steel rod to my ear and listen to various components, it really seems to be coming from the fuel pressure regulator. With this info, I then opened the gas tank cap and put my ear to the filler neck and I can hear it there also. I replaced the fuel pump with an AC Delco OEM fuel pump about 2 years ago, and this noise started about 6 months ago. Under the vehicle I hear the same sound (using the metal rod to my ear) on the fuel lines. Now that I suspected a fuel pump or regulator, I also remembered that the fuel level indicator on the dash has vibrated rapidly since I installed the new fuel pump. The rapid vibration of the fuel level indicator may be tied in to this somehow.

Lots of symptoms, now can someone provide a diagnosis? Any ideas on narrowing it down to a fuel pump or a regulator?

What sise and what engine?
Have you checked your fuel filer?
Is the fuel pressure up to par?
Have you check all ground wires to pump and fuel sending unit?

Here are the answers to some of your questions:

1. 5.7 L Vortec, K1500 4wd
2. Just replaced the fuel filter after reading your post (no change to symptoms)
3. Fuel pressure: key on, engine off -- 60 psi; engine running -- 52 psi
4. Didn't check the wiring since this would involve dropping the fuel tank. I suspect that is what is causing the flutter on the gauge. I can live with that for now.

With the fuel pressure test gauge attached, I can hit the pressure relief button on the gauge and the noise stops momentarily. I am almost certain the issue is the fuel pressure regulator. I'm going to replace it, which looks like several hours of work. Am I on the right track?

Pressure is low.
Go threw the complete fuel pressure test.
And do not forget the voltage and ground test.


The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold and fuel pressure testing guide line.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.
MT

Because the noise was coming from the regulator, I went ahead and changed it out last night. Pretty big job, but I'm glad I did it. The fuel injectors were pretty clogged up. Also found some lower intake manifold bolts loose, so tightening them probably prevented a blowout.

The noise is gone! Here are my new fuel pressure readings:

key on, engine off, pump running: 58 psi
key on, engine off, pump off: 60 psi
engine running @ idle: 54 psi
Pressure holds steady with pump off (no leakdown)

I appreciate your input. Any final thoughts?

You are welcome and thanks for posting back how it went and the fix.
Glad noise is gone.
If it is starting good cold and runs good you should be good.
Your fuel pressure readings are about 5 lbs low.
Should be 60/66 lbs.
But could be gauge off some.
You might check gauge with another one or try it on another truck.
The next time you have the gauge on it also check the direct fuel pump pressure with return line blocked or at the in line at fuel filter.
Good Luck
MT

Good post, thanks for the follow-up. I dropped you a PM to see if you had any words of wisdom before I tackle this myself this week on my Tahoe.

Because the noise was coming from the regulator, I went ahead and changed it out last night. Pretty big job, but I'm glad I did it. The fuel injectors were pretty clogged up. Also found some lower intake manifold bolts loose, so tightening them probably prevented a blowout.

The noise is gone! Here are my new fuel pressure readings:

key on, engine off, pump running: 58 psi
key on, engine off, pump off: 60 psi
engine running @ idle: 54 psi
Pressure holds steady with pump off (no leakdown)

I appreciate your input. Any final thoughts?

Excellent thread.

I only have one question for you rsmith8411 and that is: did you use a torque wrench when you tightened down the loose intake manifold bolts?

I'm ashamed to say no. I'm a mechanical engineer, and you would think I would be careful about such things. Nope. I just tightened it by feel.

I'm ashamed to say no. I'm a mechanical engineer, and you would think I would be careful about such things. Nope. I just tightened it by feel.

having torqued many fasteners over many years re-torquing this type of hardware its probably better to use feel rather than the torque spec....

if it was an r/r of the manifold/gasket and the fastener hardware was cleaned and prepared for installation the torque spec is a must...

knowing what the torque spec is is also needed before re-torquing..


I have done this re-torquing before as I was just checking the fastener security and the fasteners sometimes radomly loosen....

Thanks for the advice on this job, you're right - the coil mount isn't intuitive to put back together!

Replacing the fuel pressure regulator didn't fix my problem, so I'll be back under the hood for more fun replacing the injectors.