2nd cat...conformation/clarification

[rocko112869]

Hypothetically speaking mind you!....if i were to remove my 2nd set of cats from my 03 Grand Marquis (SCT xcalibrator2) I believe Ive read that it will not effect passing emissions because the 02 sensors are in the front cats..is that correct??? but it will cause the check engine light to come on...is that correct??? I also believe i read that i can turn off the rear 02 sensors with my SCT programmer....correct? i havent checked it yet! but if i cant a simple reflash should get the light out? conformation /clarification would be appreciated...of course this is just for FYI i would not actually remove the 2nd set of cats!...

[99SVT]

The second set of cats is after the rear O2 sensors, so no check engine light will trigger as a result. As for passing emissions, it *should* pass, but it would depend on how detailed they do the testing in your area. (visual, sniffer, dyno, state of tune, etc)

[rocko112869]

Thanks for the info...also was looking for some input as to how loud it would get if i removed em...i have duels/h-pipe/aero 2525's...it sounds good but wish it were a bit louder...im thinkin about doin just the rear cats. my buddy who does the exhaust work seems to think it will get quite abit louder. I dont want ridiculously loud? any advise/input?

[ctrlraven]

If you wanted it just a bit louder removed the rear cats will give you that. I noticed the difference in sound on mine, not stupid louder bit just a little more throatier.

[silverfox]

^^Agreed, I had my second set removed and it did help the sound a bit. No engine light as long as you leave the O2 sensors intact.

[Dennis Reinhart]

This is all true but the rear 02 heaters, and rear 02 switch needs turned off or the check engine light will come on because the rear cats have been removed, any SCT dealer can help with this.

[ctrlraven]

Dennis, the rear cats are AFTER the O2 sensors so they will not throw a CEL code. When I had mine removed I drove around with the stock tune on for a few weeks (650-700 miles) not once did the CEL come up. As long as they are still connected everything will be fine.

[Dennis Reinhart]

If you have a four catalyst syst the back two sensors moitor rear cat eff, and will throw a code if the rear cats are bad or removed.

[Zack]

If I was taking 2 of the 4 cats off my car, it would sure be the 2 closest to the exhaust manifold.

[tbone]

I had my second cats removed months ago. No light, no issues, nice sound with Magnaflows.

[ctrlraven]

If you have a four catalyst syst the back two sensors moitor rear cat eff, and will throw a code if the rear cats are bad or removed. Next time you have a panther up in the air take a look lol. The rear pair of cats are after the sensor. The sensor can not monitor whats after it. All it's doing is monitoring the after flow of the front pair of cats.


If I was taking 2 of the 4 cats off my car, it would sure be the 2 closest to the exhaust manifold. Yeah I would like to have the front pair gone. lol


I had my second cats removed months ago. No light, no issues, nice sound with Magnaflows. :beer:

[LeoVampire]

If you have a four catalyst syst the back two sensors moitor rear cat eff, and will throw a code if the rear cats are bad or removed.

I did the long tube headers and a single set of high flow cat's and I do not have a code being set nor a problem with the o2's. It's been over a year now since they went on.

[ctrlraven]

The only thing to worry about is how strict your state is on emissions and if they do a visual inspection, they might try to say something but point out there are cats on the car, pop the hood and point lol.

[Ktorres1]

What is a typical price by a shop to remove the rear cats?

[Ktorres1]

Also will it give any more air flow allowing more power etc?

[rocko112869]

How much louder/performance did rear High flow cats make it as compared to just taking them out completely? can anyone comment that has done the rear cats - high flows...then removed completely?

[ctrlraven]

What is a typical price by a shop to remove the rear cats?Most shops won't do it because depending on the state emissions laws.


Also will it give any more air flow allowing more power etc?A little more flow, I noticed slightly better mid range power.

[LeoVampire]

How much louder/performance did rear High flow cats make it as compared to just taking them out completely? can anyone comment that has done the rear cats - high flows...then removed completely?

But having the highflow single set of cats vs the 4 normal one's on the car dose make a big difference in sound and power.

And ctrlraven is correct most state laws say a licensed shop can not remove and coverters without replacing them so you might be on your own with taking care of this.

[ctrlraven]

I had a friend who worked at a shop remove mine and then placed a piece of pipe in it's place with a little bit of welding until I had a chance to get to an exhaust shop where I had them fully weld everything.

Most exhaust shops don't care how the car comes in (without cats) as long as they are not actually removing them.

[RocsMerc]

I don't know if this is to the letter of the law or not, but here in NY, as long as you have cats on the car and your check engine light is off, most shops will pass you.

[CooLManZilla]

Thanks for the info...also was looking for some input as to how loud it would get if i removed em...i have duels/h-pipe/aero 2525's...it sounds good but wish it were a bit louder...im thinkin about doin just the rear cats. my buddy who does the exhaust work seems to think it will get quite abit louder. I dont want ridiculously loud? any advise/input?


do you still have the resonator tips?
I wonder how yours sounds? I have thought about making mine a little deeper sounding. I dont know if I should do anything sometimes I like the stock sound and sometimes I want a little louder.
perhaps a little more low grumble at idle.

[rocko112869]

I dont have resonator tips...my car is just a Grand Marquis...i added the OEM crown vic PI 2nd tailpipe...no tips...everything is tucked up out of sight turned down at the ends...i kinda like it that way

[ctrlraven]

do you still have the resonator tips?
I wonder how yours sounds? I have thought about making mine a little deeper sounding. I dont know if I should do anything sometimes I like the stock sound and sometimes I want a little louder.
perhaps a little more low grumble at idle.
If you wanted just a little more grumble/rumble, remove the 2nd set of cats and you'll get it.

[03marauderon4s]

i have a 2003 marauder with flowmaster super 40s i wanna delete my second set of cats will it throw a code or mess up the o2sensor if somebody knows or has done this please help me out

[ctrlraven]

i have a 2003 marauder with flowmaster super 40s i wanna delete my second set of cats will it throw a code or mess up the o2sensor if somebody knows or has done this please help me out
Not to be rude but seriously did you not read anything in this thread? lol
Do some leg work and read and you'll find your answer.

[03marauderon4s]

hey man im new to this it was my first day on here and there is people saying it does and people saying it does not throw codes so tryin to find someone who did it i do not wanna ruin my car

[fastblackmerc]

hey man im new to this it was my first day on here and there is people saying it does and people saying it does not throw codes so tryin to find someone who did it i do not wanna ruin my car

I had my entire exhaust system replaced. Two hi-flow cats in place of the four stock cats. The O2 sensors are before the second set of cats so removing anything after the O2 sensors should not cause a code to be generated. As for the vehicle inspection, the techs that do it just look for cats. If they see 2 they are happy. They have no idea that the Marauder came with 4 cats.

[03marauderon4s]

thanx for your help man thats what i thought im good we do not have emissions in minnesota

[justbob]

Kind of an obvious question here........ But I still have my extra set of mid pipes laying around with the neutered rear cats and was contiplating gutting the front converters. 1st, would this mess with my tune too much? 2nd, Would it through a light? I would imagine yes and yes. Just thought I'd atleast ask before I waste my time with a BFH. Thanks.

[fastblackmerc]

Most "reputable" exhaust shop will not remove any cats.

[RacerX]

Kind of an obvious question here........ But I still have my extra set of mid pipes laying around with the neutered rear cats and was contiplating gutting the front converters. 1st, would this mess with my tune too much? 2nd, Would it through a light? I would imagine yes and yes. Just thought I'd atleast ask before I waste my time with a BFH. Thanks.
If you neutered the rears and you didn't throw codes, you won't by getting rid of the primaries. The first O2 set is before any cats. If the rear set is turned off, the first set doesn't know what the heck you have downstream. I don't have any cats, no tune probs, stock mufflers though. Soon to be all new exhaust... ;)

P.S. Use an electricians big bore drill bit. Works around corners, no hammer. Just don't breathe that crap either!

[justbob]

Well now, that makes sense. I might try it seeing as this one set I have is clogged anywho. Thanks.