03 GMC 5.3L
228/588 cam.
Stock manifolds
Custom Y pipe to Gibson Cat back. 3" electric cutout.

It sounded great, then I removed my cats.

Now there is a nasty BAAAAAA at certian engine loads. I changed the muffler and I have the same noise.

Any thoughts?

I am lamost certian it has to be comming from the factory Y where the two pipes merge.

 

It's probably because you're running super rich. I had the same problem and it's because my engine runs super rich right around 3k-3200 rpms.

 

Thanks for the reply.

But It runs great.

I did a closed loop SD tune for the VE, then tuned my MAF. And I run a PLX Wide band. Verified my PE and logged everything. It's not running rich. Stays right around 14.7 when dirving.

I still hear the sound through the cutout (although much louder) so I know it's not in the muffler. All I can think of is the pulses hitting each other at the Y??

 

manifold and the y pipe are what is causing it.

 

i have the same problem with my LTs, no cats, and Aerochamber...

 

is it just a steady deep sound or more of a rattle sound?

 

It's like a rattle. But it is def not a mechanical rattle.'

Man the first time I started it without the cats I thought every baffle in the muffler was blown loose!

But like I said its not it makes the noise to the 3" cutout.

I have a complete custom Y but I still use the factory part where it connects to the 3" section.

I can't live with this noise!

 

So you also have a nasty sound with headers and no cats?

Do you use part of the factory Y pipe.

This means my factoy manifolds are not to blame I guess?

 

mine is like that, I bought a new muffler and welded it in and same thing. I moved the Y closer to the headers and it helped a little. It kinda seems that the pulses dont have enough time to mix together or something. Any help would be great.

 

Well at least I know Im not alone!
I thought about redoing everything and running 2/ 2.5" pipes straight back inplace of the one 3" eliminating the Y.
But that's alot of work and then throwing the money away on my new exhaust and 3"cutout!