Boy, do I have a weird one going on, I am stumped

[MTboatguy]

I am coming back from town today and I stopped to check on my 5th wheel, left the truck idling, when I returned to it, I hear a higher pitched tone from under the truck, almost sounds like a continuous seat belt warning tone. Easy to hear, most intense between the bed and the cab. Turned the truck off, asked my wife to listen, when I started back up, no noise, the truck ran for about a minute, then the tone/noise started building again, almost sounds like a major vacuum leak, but I don't know of any vacuum lines that run in that area.

This is the 99 Silverado, Z71 5.3 liter that I received when my Dad passed away a few months ago, but I swear, I have never heard a noise like this on a automobile. I have no clue what it could be!

Anybody else heard something like this in their truck? I know quite a few on here own Silverado's, so figured I would ask before taking it in, to at least know what I am looking for.

Thanks in advance.

 

[Bob_VT]

Sounds like you might have a fuel pressure bleeding off There is 50-60 PSI of fuel pressure in the chevy V-8 tanks and sometimes when the pump goes bad it will bleed off When it does it again rmove the fuel cap and listen for gurgling and it is another indicator the pump is old

 

[Bob_VT]

Chevy designed the systems to "hold" fuel pressure in the lines which helps in starting. My older chev truck has an old fuel pump so when I go to strt it I turn on the key and wait 10-15 seconds befor I engage the starter so mine will build pressure

 

[thumpar]

Chevy designed the systems to "hold" fuel pressure in the lines which helps in starting. My older chev truck has an old fuel pump so when I go to strt it I turn on the key and wait 10-15 seconds befor I engage the starter so mine will build pressure

I do the same with my 5.3l Yukon. If not it just cranks unless it has been run very recently.

 

[bruceb58]

The ABS control unit sits under there on the left side of the truck. Is that where you heard the sound? They are known to fail. Mine failed but it stayed on even with the ignition off. Only way I could get mine to turn off is to pull the fuse in the fuse compartment under the hood.

If that is your issue, there are places on eBay that sell repair services. Mine went out again after the initial repair but the guy guaranteed his work and repaired it again.

Not saying it is your issue but it is worth a look.

 

[bruceb58]

I do the same with my 5.3l Yukon. If not it just cranks unless it has been run very recently.

There is a small pressure regulator on the fuel injection system that can fail and cause this condition. It has a vacuum hose that runs to it. If you pull off the vacuum hose and it has fuel in it, the diagram has ruptured and you need a new part.

 

[rbh]

Is the fuel pump in the tank or mounted on the frame rails?

 

[bruceb58]

Is the fuel pump in the tank or mounted on the frame rails?

Tank

 

[MTboatguy]

Took the truck to the garbage dump this morning, 40 mile round trip, no sound at all, hmmmm

 

[bruceb58]

If it was the ABS, it will likely be a hard failure. The circuit board in the control module has some driver FETs that blow out and the repair service just removes them and solders in new ones.

 

[MTboatguy]

If it was the ABS, it will likely be a hard failure. The circuit board in the control module has some driver FETs that blow out and the repair service just removes them and solders in new ones.

I agree, I don't believe it has anything with the braking system, I am really thinking it is something in the vacuum system.

 

[bruceb58]

I agree, I don't believe it has anything with the braking system, I am really thinking it is something in the vacuum system.

You would be surprised. When the ABS fails, this little pump motor starts running and won't stop and it sounds like what you described.

 

[MTboatguy]

You would be surprised. When the ABS fails, this little pump motor starts running and won't stop and it sounds like what you described.

Like I said, I drove it for 40+ miles this morning and no weird noises, I am hoping this afternoon it warms up a bit, and then perhaps it will start again, so I can crawl under it and start tracking it down.

 

[keith2k455]

Between the bed and the cab would point me to the transmission. After here I just start guessing.

 

[MTboatguy]

Between the bed and the cab would point me to the transmission. After here I just start guessing.

In this truck, the transmission sits forward of the separation between the cab and the bed, it is a single cab with a short bed, no extended cab, tail shaft is about 6 inches ahead of the joint. But as I said, I have actually drove it over 50 miles today and it is not making noise and I have no codes showing up, so I will keep monitoring to see how this pans out.

 

[keith2k455]

This is a stumped for sure. It will most likely be back, but I'm sure once it does you will catch it before something bad happens.