Whistling? (and not Dixie) from under the hood . . .

[captaincrunch]

Whistling noise under my hood. I hear it at about 1500rpm and again about 2000 or so (but not as bad). Always the same tone, and only slightly changes with rpm changes (range of 100rpm or so).

I've recently added gears for timing and also recently changed my L56 intake for a L65 and cut out my plenum and removed the EGR.

Here's my thoughts:

Intake manafold leak? - maybe something's not sealing right

Plenum leak? - I didn't use a gasket, only sealant.

Turbo hose-to-plenum leak? - Would this cause a whistle?

New Gear drive whine - maybe, but it really sounds more like a whistle.

Is there positive pressure inside the manifold or negative. I'm assuming postive due to the turbo, but I don't know enough about it and maybe it's a suction from the cylinders.

What's the best way to check for manifold leaks?

"I feel a lot more like I do now than I did when I first got here"

[DennisG01]

Forgive me for possibly stating the obvious, but could it be that with the changes you made you can hear the turbo easier?

[captaincrunch]

Yeah, thought of that. But, it's not a whine . . . and I didn't notice it until I had the gears/HO water pump/injectors/glow plugs installed.

I had been driving the truck for a few days with the new intake and don't recall hearing it. However, my harmoinc balancer had separated and there was a terrible rattle at idle. They found it when installing my stuff.

I also don't recall hearing it JUST AFTER the gears and HO water pump were installed. Seems I started noticing it about 3-4 days later. But, there were a lot of new noises (more rattle) that captured my attention and I may not have heard it.

Just seems a lot more now. That's why I'm leaning toward a leak somewhere. Sounds a lot like a vacuum leak, but it's not constant - only at certain RPM's.

I'm going to investigate further tomorrow. Just thought I'd tickle someone's thoughts to guide my search. Just in case this is normal with the gears installed.

[CareyWeber]

Could be the fan belt idler pulley bearing.

[DennisG01]

OK. If you think it might be a vacuum line, then here's an uneducated guess (someone correct me if my train of thought is wrong):

If it's a vacuum line, then you would be getting less boost, which could equal more black smoke? Do you also have less power? Do you have a boost gauge?

[captaincrunch]

Nope . . . no smoke, great power since new injectors and gears. Again, that's something that leads me to an intake leak.

I read something about leaks around the turbo hose-to plenum seal. Wondering if this could be it.

Gonna be cold and rainy in Atlanta tomorrow, a good day to work in the garage. I'll dive into it then.

[markrinker]

(...read this in your best Jeff Foxworthy voice)

"Damn Captain, I'll come on over and help you unbolt the hood. Then you climb on up in thar and we'll take her for a spin, with you sprayin WD-40 ever-where until you find the leak. I promise not to mash on the brakes none."

Seriously, you can sometimes find intake leaks using WD-40. Let the truck idle (in PARK and with the e-Brake set), and spray SMALL amounts of WD-40 at any suspected leak location. You'll hear the engine RPMs increase if it finds a significant path into the intake.

DO NOT SPRAY WD-40 DIRECTLY INTO THE INTAKE. RUNAWAY ENGINE CAN OCCUR - DON'T ASK HOW I KNOW THIS, ITS TOO EMBARASSING TO TELL.