Exhaust/vacuum leak?

[swathdiver]

Could be in the early stages of failing. You could try clearing any deposit build up by getting them really hot by holding the motor in 4th gear and running it up to 3000 rpms for a few minutes or so on the highway.

What grade of fuel are you running? If you're up north winter blends are not as engine friendly as regular. Maybe run a tank of E85 through your L94. The motors love it.

 

[jyi786]

Could be in the early stages of failing. You could try clearing any deposit build up by getting them really hot by holding the motor in 4th gear and running it up to 3000 rpms for a few minutes or so on the highway.

What grade of fuel are you running? If you're up north winter blends are not as engine friendly as regular. Maybe run a tank of E85 through your L94. The motors love it.

Ok, I did this. Ran the engine between 3000 - 5000 RPMs on the way home and held it in 2nd gear (couldn't do 4th because I wasn't on the highway). It seemed to run just fine.

It's a Denali, so I always, unfailingly use 93 octane. I also already used the Chevron complete fuel treatment already a few weeks ago. I don't do this all the time, only on occasion.

 

[jyi786]

I know it's a completely different vehicle, but this is exactly what it sounds like.

 

[swathdiver]

I'd go with a vacuum leak.

 

[Doubeleive]

you can get a cheapy stethoscope at the autoparts store and poke it around inside the engine compartment to narrow it down, or even a piece of small tubing and some vacuum hose held up to your ear will work just fine as well.

 

[gpracer1]

If you suspect a vacuum leak, maybe check the brake booster, line from booster to back of manifold.

 

[jyi786]

Wanted to update this thread.

Ever since I did what @swathdiver told me to do, the startup "choke" has been practically eliminated. It's 33 degrees out right now, and I just started it up cold. No hesitation/choke. Yesterday was 22 degrees, and it didn't do it either. I even took a video of it.

Also, I'm beginning to think the "hissing" is me being paranoid. Here's a review of the exact same vehicle (sans being an XL), and I'm hearing the same "hiss" in the video.

 

[Doubeleive]

mine doesn't sound like that, there may be a tiny tiny hiss but that's it

 

[jyi786]

mine doesn't sound like that, there may be a tiny tiny hiss but that's it

Hey, thanks for that! That's how mine sounds to a T!