Bad Catalytic Converter????

[Sergio Luevano]

I am having an issue with my 2007 yukon 5.3L engine. It started with a check engine light and then, when I would accelerate after 4500 RPM there is a loud bang from the back end. I have knocking noise every morning that goes away after 30 seconds. Took it in to the dealer and apparently the only thing my extended warranty does not cover is the issue. They are claiming that the loud band and the knocking noise every morning is caused a catalytic converter going bad so they want $1,700. The knocking every morning goes away when it warms up after about 30 seconds. Doesnt make sense? Any help?

 

[Brian Wilson]

The knocking comes frome where? Do you have a stethoscope?

 

[Sergio Luevano]

I hear it coming from the engine, but dealer saying its the catalytic converter. I will see what the codes are myself on the check engine light to see if anything paints toward cat. The engine is burning roughly between a quart and half to two between oil changes, which is not normal, but they say it is. I run full synthetic, which people have recommend regular oil.

 

[Brian Wilson]

Check to see if you have broken exhaust manifold bolts. That is common

 

[CrashTestDummy]

Odd that the cat, which is part of the federal emission control system, is the one thing not covered under your warranty. They're usually covered 10/100,000, at least.

I have what I think is a broken (again) cat on our 92 Camaro B4C. It sure rattles when cold, and gets a bit quieter when warmed up. I haven't changed it yet. I'm waiting for the car to age out past emissions testing, then I'll go ahead and clean the rest of the cat out.

 

[Zumwalt]

i had an 03 that did that. i thought it was the engine till i got it up on the lift and knocked on the cats and thats what it was... dont go much longer with it rattling.. i did.. it clogged both cats and backed up into the engine and now i have a new engine and cats...

 

[Sparky_69]

Try this test, only requires a vacuum gauge.

 

[sick1166]

my cat was bad 07 85000 just past the warranty of emissions 8 years 80000 drove for 6 monthe than the embarrassment of the loud rattling in my neighborhood i went and got some muffler shop $500.00 bucks and had check engine light on for years with bad cat code just went to exhaust shop and he told me those cats i got are junk he put new ones on a runs perfect know MY advice get oem cats 2 cats installed $800.00