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Old 02-09-2014, 08:39 PM   #1
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Learn me some Pre-Cat delete...

Didn't find anything in my search.

Patient: 05 TJ Sport with dual pre-cats immediately below the header.

Can pre-cats be deleted without upsetting the ECU?

Does anyone sell an exhaust system that is a header back that deletes the pre-cats?

Inquiring felines wanna know

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Old 02-09-2014, 09:14 PM   #2
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I have gutted my pre cats due to some previous problems, it didn't throw codes at first but now I'm getting two P0421 and P0431 (bank 1 and 2 warm up catylist). I am also trying to figure out options to bypass this, or new exhaust system. I haven't found a way for it to pass without them. Been doing some research but no luck *Subscribed*

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Old 02-09-2014, 11:07 PM   #3
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Ive thought of the idea so I looked into it a bit and heard mixed stuff but mostly heard if you pull the sensor out of the exhaust pipe a little bit using a spark plug non fouler it doesnt read as well wich shouldnt code. I have yet to hear of any performance gains from doing this wich is why I have not done it. Also I have heard of dummy sensors that are sold, if you do enough research im sure you can find what tthe neaded resistance of the sensor is and make your own.
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Old 02-10-2014, 09:29 AM   #4
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I have a 2001 TJ w/ pre-cats, w/o down stream cat, my buddie has 2000 TJ with straight head pipe, no pre-cats, OEM head pipe. You could order older head pipe and adapt O2 sensors. (Im sure you could find a work around for the O2 sensors all you need is the right resistors to fool sensor) 2000's have O2 sensor at downstream cat. Or just weld bungs into pipe screw in sensors. Just my 2 cents good luck
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Old 02-10-2014, 11:10 AM   #5
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Quote:
Originally Posted by bluevr6 View Post
Can pre-cats be deleted without upsetting the ECU?

Does anyone sell an exhaust system that is a header back that deletes the pre-cats?
No.

and yes, you can make one.
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Old 02-10-2014, 11:38 AM   #6
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So if you want to pass an inspection, you must have the per cats 100% functional? Is OEM the best route for replacement? Do you recommend a specific brand or type of exhaust for replacing stock?
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Old 02-10-2014, 11:45 AM   #7
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So if you want to pass an inspection, you must have the per cats 100% functional? Is OEM the best route for replacement? Do you recommend a specific brand or type of exhaust for replacing stock?
yes. with no CEL's.
yes, if you can afford it.
Walker Exhaust, among others, sell stock-type replacement stuff for much better prices than OEM....all readily available from Advance Auto, AutoZone, RockAuto, etc.
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Old 02-10-2014, 12:09 PM   #8
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I bought a magnaflow high flow replacement with all three catalytic converters off amazon and I've been incredibly happy with it.
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Old 02-11-2014, 12:37 AM   #9
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If you go aftermarket make sure there carb aproved if you live in ca, I work in a shop that does smogs and if the smog tech notices aftermarket cats he always runs the p/n to see if there aproved. Even then sometimes they dont work well and fail the taipipe but have only seen that happen on honda
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Old 02-11-2014, 07:17 AM   #10
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They make a couple different versions of the magnaflow setup. I'm not sure about magnaflows reputation around here but I'd say the quality is superior to OEM.
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Old 02-27-2014, 10:51 PM   #11
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Just replaced mine with an Eastern full system from RockAuto for less than 300. It's direct fit, but I left the main cat off. Originally gutted the other pre cat after throwing a code and finding the blown one. Ran it like this for a few months but still got CEL. I also used the spark plug fouler trick, but continued to throw codes. Jeep was also drinking fuel. I was getting about 8-10 mpg on a good day. Only other option I've heard of is the O2 sensor dummies. For reference, mine's an 04 Rubi. Good luck.
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Old 02-28-2014, 08:19 AM   #12
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You cannot replace the sensor with a resistor to fool the system because the O2 sensors are not resistance sensors they actually generate a small voltage which varies from 0 to .9 volts based on O2 gradient inside exhaust to outside air.
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Old 03-18-2014, 03:00 AM   #13
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I was looking at running my own exhaust system from the headers back. I have the split header setup. I was planing on removing the pre cats and changing the main cat to a flowmaster #2000125. According to them this cat can handle up to a 5.7L motor and vehicle weight of 6K lbs. I would leave the pre o2 sensors in place and move the rear two to behind the new cat so hopefully i wont get any CEL's. Will this work and still pass and emissions test?
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Old 03-18-2014, 08:52 AM   #14
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I used to work for an emissions company here in colorado and I can say this, the company knows how many cats each car has and they look for them. If you don't have them you fail. If you can do a drivethrough emissions test than its up to how good your system is, you may or may not fail. On the tests that you just drive through its all about numbers. If you have to get out of your car and let them expect it for the emissions system, it will fail.
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Old 03-18-2014, 01:09 PM   #15
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Even if they test what's coming out the exhaust tip. I don't currently live were they test emission but I will be moving in the future.
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Old 03-18-2014, 01:25 PM   #16
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If they know you are supposed to have 3 and you only have 1, you might fail even if what comes is cleaner. I knowbit sounds stupid but its the system. Its part if why I dont work for them

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