CEL & Catalyst Removal - Cherokee SRT8 Forum
View Poll Results: Which is better?
CEL is on & straight pipes 1 9.09%
Race Cats and NO CEL 10 90.91%
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post #1 of 13 (permalink) Old 10-27-2006, 05:28 PM Thread Starter
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Thumbs up CEL & Catalyst Removal

Guys,
Most of us were wondering about Mid pipes and Associated CEL. I wanted to put this for everyone and share the most accurate knowledge from our experts here.

Usually Catalyst Removal adds some easy power. But in Modern vehicle, the ECU is programmed in such away with the reading of the sensors just after the Cats. (said by one engineer at Jeep)
CEL usually will the hurt the HP by going in such safe mode ECU mapping as far as i know..

Do you think that the gained HP by Removal of Cats worth the CEL?
Do you think that the gained amount of power from the removal, will not be effected by the CEL and the ECU going in such mode?

I think it will hurt, I have seen such situations.. Now i need your Feedback with explanation if any?

IMO: put Race cats and floor it
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post #2 of 13 (permalink) Old 10-28-2006, 03:48 AM
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Re: CEL & Catalyst Removal

first off, let me start by saying that the knowledge i have about o2 sensors and their effects on performance are from my personal experiences with my G35, and the members of G35driver.com and My350z.com, 2 online forums like this one with LOTs of expert members......

all things being equal (i.e. if the computer doesn't interfere) you will gain power by freeing up the extra exhaust flow

most newer cars use 2 sets of o2 sensors...
primaries which are in the headers (before the cats) and secondaries, which are after the cats.

the primaries are the wideband o2 sensors that the computer uses to make adjustments to the AFR/timing/tune etc. basically those are the sensors that give continuous feedback to the ECU and control the running of the motor.

the secondaries are ONLY there to tell the computer that the stock cats are doing their job... that is the only information they pass on to the ECU (and on some cars they make small adjustments to the long term fuel trims, nothing noticeable or necessary)

problem is, when you DO remove the cat, the secondaries tell the ECU that it's emissions gear isn't working, and it puts an electronic chokehold on your power.

tricking the secondary o2 sensors into thinking that the cats are still functional (by using some form of "sim box") should not in any way harm the motor or anything on the car, and will allow you to realize the gains you should be getting by removing the OEM cats. a sim box will simply tell the ECU, "hey guy, no problem down here, your restrictive OEM cats are still A-ok!" meanwhile you're running open pipes and gaining power

the issue has to do with phasing between the voltage readings on the primary and secondary o2 sensors in each exhaust tube. for example...

if the primary sees: ~~~/\~~~/\~~~/\~~~
and the secondary sees: ~~~/\~~~/\~~~/\~~~

then the computer knows that there is nothing in between altering the exhaust gasses (no cat converter present). a sim box might alter the second signal to show ~~~^~~~^~~~ which is less voltage fluctuation, which makes the computer think the cats are stil there

have i confused anybody yet?
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post #3 of 13 (permalink) Old 10-28-2006, 03:57 PM
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Re: CEL & Catalyst Removal

We had two trucks moded with the same mods exactly, one had race cats and the other had nothing.
Guess what? the one with the race cats kicks out the one with No cats and CEL on.

I saw it myself. stick with race cats for performance applications
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post #4 of 13 (permalink) Old 10-28-2006, 05:02 PM
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Re: CEL & Catalyst Removal

Quote:
Originally Posted by EXTM
I saw it myself. stick with race cats for performance applications
personally i agree with you 100%. i have been running high flow cats on my car for almost 2 years... they provide almost all of the gains that a straight thru test pipe would give, without any of the drawbacks
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post #5 of 13 (permalink) Old 10-29-2006, 11:14 AM
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Re: CEL & Catalyst Removal

Is there ant websites where i can purchase a high flow cat????
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post #6 of 13 (permalink) Old 10-29-2006, 02:01 PM Thread Starter
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Re: CEL & Catalyst Removal

Quote:
Originally Posted by slickrich555
Is there ant websites where i can purchase a high flow cat????
Magna flow sells them and KOOKS does too. They shouldnt be more than $100 for a pair.
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post #7 of 13 (permalink) Old 10-29-2006, 05:56 PM
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Re: CEL & Catalyst Removal

the Kooks header setup comes with a mid pipe and high flow cats. This system sets off CEL lights and causes problems. Will replacing the kooks highflow cats with other cats fix the CEL problem???
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post #8 of 13 (permalink) Old 10-30-2006, 01:28 PM
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Re: CEL & Catalyst Removal

Quote:
Originally Posted by unclgreggy
the Kooks header setup comes with a mid pipe and high flow cats. This system sets off CEL lights and causes problems. Will replacing the kooks highflow cats with other cats fix the CEL problem???
Interesting Question Greg, not sure on that one, I'd probably say no tho. Greg why don't you try the O2 Sim Box from GSM? That should fix you up. Let us know how it works bud.

Mike B. GO Cleveland Clowns, OH
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post #9 of 13 (permalink) Old 10-30-2006, 01:43 PM
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Re: CEL & Catalyst Removal

the Gs sim box does not work period. the are in the process of reconfiguring it to work.
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post #10 of 13 (permalink) Old 10-30-2006, 10:32 PM
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Re: CEL & Catalyst Removal

My experience with this type issue is that the cats may have been relocated to far downstream to remain fully functional. Between the heat loss of the headers and the relocation to an area south of optimal placement, the hyper sensitive ECM may be spitting code due to the fluctuation of cat efficiency.

If this is indeed the case, then all the downstream sensor work is for naught. The trick is going to be opening the box of vodoo and getting proper tune language downloaded. Cobra 'Stangs had the same prob until the tuners figured Fords top secret super friend handshake. Then the skys opened, the sun came out and ECM tuning was viable. This is what the tuners should be doing as we speak...not the ole "trick the ECM until it learns our trick" syndrome.

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