Exhaust/vacuum leak?

[jyi786]

My truck is a 2012 Yukon Denali XL. Recently, I started noticing a very loud hissing sound emanating from around the bottom driver's side of the truck. It sounds either like a vacuum or exhaust leak of some kind. The noise is most prominent by the driver's wheel area. Just stand there and you can hear it.

Another thing I noticed is a difference in the way the truck starts when starting cold. My truck normally starts very strongly, but as of recent, it will slightly "choke" when starting, then rev up to normal. I wonder if these two issues are correlated?

I also *thought* I notice the truck struggling to pull when I hit the throttle, but right now it feels more like placebo effect than anything.

I have had direct experience with a catalytic converter failing. It failed on my Olds 88. It caused the car to be unable to shift to second. I have no such issues with my truck, so I'm not sure if that's it.

What do you all think? Is this maybe nothing and I'm just being a bit paranoid?

 

[kbuskill]

You didn't specify front or rear wheel well.

I would slide under the truck and see if you can locate the source of the sound.

 

[jyi786]

You didn't specify front or rear wheel well.

I would slide under the truck and see if you can locate the source of the sound.

Oh my bad. I thought that saying "driver's wheel well" indicated that it was up front.

 

[kbuskill]

Oh my bad. I thought that saying "driver's wheel well" indicated that it was up front.

Drivers side has 2 wheel wells... lol

 

[jyi786]

Drivers side has 2 wheel wells... lol

Lol

So yeah, I can hear it the most when I stand right outside the driver's side door up front.

 

[kbuskill]

I would slide under and take a peek and have a listen. Could be fuel pressure related but I would think you would smell gas.

 

[denalianyone]

Probably cat on the left babj


Sent from my iPhone using Tapatalk

 

[swathdiver]

A bad cat should throw a code P0420 or P0430 if you have working lower O2 sensors. Mine does everyday! Don't think an exhaust leak, unless you blew a header gassket would cause the motor to stumble, that would more likely be vacuum related an intake gasket or such.

 

[denalianyone]

A bad cat should throw a code P0420 or P0430 if you have working lower O2 sensors. Mine does everyday! Don't think an exhaust leak, unless you blew a header gassket would cause the motor to stumble, that would more likely be vacuum related an intake gasket or such.

It should as you say but a rattling cat can sometimes not throw a code. I had that experience.


Sent from my iPhone using Tapatalk

 

[jyi786]

Yeah, I'm not hearing any rattling can sounds, the truck doesn't really stumble, nothing that I can discern except the hissing and the slight choke on start (in 20 degree weather or so). And no codes are being thrown either.

I don't know if this is related, but sometimes, after a long drive, when I get out of the truck and it's still running, the exhaust smells a bit foul.

 

[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!