Hmm? new coils new gaskets....still a problem

[Gcolladay]

I've got an 03 ls v8 premium with 110k on it.I just replaced all the gaskets n two coils.A week later the CEL light came back on.A little bit ticked after dumping time and money into it,I took it down to advanced auto so they could pull the code. the guy said it was either a vacuum leak,or an o2 sennsor.I thanked him for narrowing it down and went on my way. A week ago it started too bog down real bad. So I disconnected the battery and check the coil wells for leakage.None. after putting everything back the CEL went off ofcorse,i took it for a ride.Now I can't even get it above 40mph,it sounds like a top fuel dragster,and shifts real hard .I'm also hearing a rattle under the car when I "try" to accelerate....I went ahead and ordered the rest of the coils. But does anyone think this could be a clogged cat or bad o2 sensor? if so how may times do I have to run the car to get the pending codes to come back...(CEL) I've always maintained my ls real well I'm just a little dumbfounded.....

 

[nickandersonLS01]

it doesnt feel like the trans?

 

[hrmwrm]

if it's not misfiring, it's not coils. melted out cat can cause rattles. if it turns out to be the cat, change 02 sensor as well, or it will be short time before it happens again.

 

[02V8Sport]

It could be a clogged cat. my 04 had one very early in its life and the dealer replaced it and ran fine since. My car would go about 30mph with the car floored before I pulled over and had it towed in to not damage the motor.

 

[MDavis0424]

The CEL codes should come back as soon as the PCM sees a problem. The trans will shift hard for a while after the battery has been disconnected until the trans relearns the shifts. You say it sounds like a dragster, do you mean the RPMs are going way up but not shifting into higher gear? Did advanced auto tell you what the actual codes were?

 

[eastcoastLS]

It could be a clogged cat. my 04 had one very early in its life and the dealer replaced it and ran fine since. My car would go about 30mph with the car floored before I pulled over and had it towed in to not damage the motor.

my exhaust blows harder on the driver side than the passenger side, could that be a clogged cat?

 

[97stscaddy]

Hard shifting, no power, rattling under the car = busted cat The rattling is some pieces of the "honeycomb" inside that have broken off and are bouncing around and blocking the flow of the exhaust. I wouldn't recommend driving the car in that shape.
If you need the car but cant get the new cats right away, separate the system at the halfway point between the cats and resonators (there should be a set of factory clamps there), drop the cats down from the manifold and gut 'em. It'll sound louder, and stink like a big old V8, but it'll drive like new. And the CEL will probably come on. But you can ignore it until you get the cats replaced.

my exhaust blows harder on the driver side than the passenger side, could that be a clogged cat?

Possibly. Usually a clogged or partially clogged cat will get hotter than normal. If you can get your hands on an infrared temperature sensor (you can get them at hobby stores), drive around with your foot on the floor for a few minutes, then stop and check the temperature. If one side is significantly higher, its probably clogged partially.