cat removal question

[richard cheese]

im getting set to remove my cat, and replace it with a flanged straight pipe, as well as flanging the cat to replace it when i have to start smogging my truck next year:icon_bsEFFE YOU CALIFORNIA)

my b.i.l., who is a diesel tech at a local big rig shop told me that the computer in my truck will throw a code without the cat on, and store that code in memory, so when i do get it smogged ,they can see the code, and I will get a hefty fine

my question is this

is he full of shit about the computer storing the code (as i know 03's under federal emmisions guidelines didnt have a cat....but the same computer)

thanks in advance

 

[Unit453]

Dont listen to retards who claim to know these trucks.

I've taken my cat off from a 2nd generation and a 3rd generation(<---North East truck = Cali emissions) and I've never gotten a code. I highly doubt you'll get one at all.

 

[625fireman]

Dont know where you are but in ohio they actually look to see that the cat is there. There are other ways around it though. cut the cat in half clean the crap out and wled the two halfs on to a straight pipe then everyone is happy.

 

[RVC]

I just knocked the guts out of my CAT.

 

[richard cheese]

im going to have a shop expand both tubes going in and out of the cat and and some extra pipe so it slips over the existing exhaust.

that way i can interchange the cat and the straight pipe pretty easy

 

[Unit453]

I didnt realize I just called your B.I.L. a retard until now. I guess I'm the retard so no offense for that and I do apologize.

 

[GMCYA]

There are no sensors in the exhaust so how would the truck know that the kitty ran away? I never got a code on my LBZ from straight piping it.

 

[richard cheese]

I didnt realize I just called your B.I.L. a retard until now. I guess I'm the retard so no offense for that and I do apologize.

dude....who gives a **** Nick?? lol...put the bong down man...yer gettin paranoid :lol:

no offense taken man..cause sometimes HE IS A TARD

:LOL:

:thumbsup:

 

[Foreman00081]

your bro in law is definetly wrong on that one. how does he think it will throw a code if theres no O2 sensor on the cat to tell the computer that its not there? and as far as doing all that work to the stock cat pipe my suggestion would be to find a front pipe from a fed LB7 and just switch them back and forth when and if you have to have it smogged. i got one from a member on DP for 50 bucks shipped last year and i kept my stock pipe with the cat just in case.

 

[saratoga]

It's not because of an O2 sensor... the cat's restriction actually provides the backpressure needed on the upstream side of the exhaust to force exhaust gasses back into the intake when the EGR valve opens. There is a pressure differential created and this is picked up through the change (reduction) in airflow past the MAF since the engine is now sucking exhaust gasses back into the intake. That's how the computer knows it is working and is the reason SOME- not all trucks set the CEL for EGR and or MAF codes when the cat is removed.

 

[Unit453]

And cats have been proven to actually flow quite well. A cat back exhaust system has been dyno proven to provide an additional 11 hp. Most of the restriction from what I understand is from the stock tubing size and the muffler.

I ran a cat back when I first started modding my truck, back when I lived in NY where its equally as communist as Cali standards. I wouldnt ever pass inspection if my cat wasnt there, let alone a sniff test. When I moved here and got situated, I went with a full 4" system to replace my rusty cat back. I actually put on a resonator as well. Its welded right where the cat used to be at. Its a nice sounding system (MBRP) and it isnt loud at all. I can kick myself in the ass for not doing this from the beginning. I also thought that when I took my cat off, since I have a north east truck (which is the same as Cali emissions as of 2006), my engine light would go on right away. My EGR valve did happen to go bad right afterwards though. Not sure if it had anything to do with it or not.

 

[socal2ks]

My only concern while in CA is the roadside sniffer/inspection setups.

All it would take is a mirror to look under the truck for a cat.


Any tips on hollowing one out?

 

[db9938]

It's not because of an O2 sensor... the cat's restriction actually provides the backpressure needed on the upstream side of the exhaust to force exhaust gasses back into the intake when the EGR valve opens. There is a pressure differential created and this is picked up through the change (reduction) in airflow past the MAF since the engine is now sucking exhaust gasses back into the intake. That's how the computer knows it is working and is the reason SOME- not all trucks set the CEL for EGR and or MAF codes when the cat is removed.

So a blocker plate would, in theory, also change the differential and potentially throw a code?

 

[saratoga]

Yes if you don't install a finger stick or use EFI to disable the EGR it will set codes.

I have my EGR motor removed from the valve (jerry-rig way of disabling the EGR)- it's still plugged in, just sitting on top of the heater hoses now. Truck will throw a P0401 and P0403 occasionally. I could care less because I just use my scangauge to clear the codes.