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Off road exhaust system that won't set TC's

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Old 08-07-2013, 11:03 AM
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Default Off road exhaust system that won't set TC's

Is there a way to pull the cats out of the exhaust without setting codes? (96+) I'd rather not have them in my car when it's finished, one less thing to go wrong.

Worst case scenario I'd just let the codes set, and pull the bulb for "check engine" and ignore it. Ideally I'd like to keep it functional since it does serve a purpose.
 

Last edited by Crackers; 08-07-2013 at 11:12 AM.
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Old 08-07-2013, 01:00 PM
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You can get the ECM reprogrammed. There is very little performance gained by removing them, not to mention it's illegal to remove them even if doing an engine swap into ANY vehicle that is road legal in most parts.

As a side note my '96 still has the original cat, and O2 sensors, so they must be fairly reliable...
 
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Old 08-07-2013, 01:11 PM
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I bought my 95 CPI a while back and the only thing on it was a glasspack or cherrybomb that someone put on to replace the cat. I dont know if they did that for quietness or to sell the cat for the $$$? It goes manifold gp cb to straight pipe out the back. It is quiet as can be. You can hear a little exhaust note if you get on it but not much. The CEL is not on nor is it throwing any codes. I hate quiet so I am cutting the gp cb off and going super 44 or super 10. I am leaning more towards super 10 with 2.5" before and 2.25" after exiting 90 behind the tires I would do in front of the tires but no room on the drivers side due to the leaf springs and the frame.
 
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Old 08-07-2013, 03:09 PM
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It's not about performance, it's about minimalizing the number of things that can go wrong.
 
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Old 08-07-2013, 04:28 PM
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If it does cause a CEL, you can always put a spark plug non fouler on the o2 sensor to raise it out of the exhaust stream and fool the computer
 
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Old 08-07-2013, 04:36 PM
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o2 eliminators, I know jegs used to sell them
 
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Old 08-07-2013, 08:14 PM
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Originally Posted by 4X4GS10B View Post
o2 eliminators, I know jegs used to sell them
Sweet, thanks. I did a google and found some that I can hide in the loom even. That way it's not like "Hello, something's missing!"
 
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Old 08-07-2013, 08:16 PM
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Originally Posted by 50lb_cat View Post
If it does cause a CEL, you can always put a spark plug non fouler on the o2 sensor to raise it out of the exhaust stream and fool the computer
Yeah, I've seen that before. Just looks kinda ugly, thanks though.
 
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Old 08-07-2013, 09:34 PM
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The aftermarket "foolers" apply a constant low voltage to the downstream O2 signal wire to the PCM. When the PCM randomly runs the catalyst monitor, the oxygen sensors must respond with the correct data at the correct time. Save your money. If you can find someone to delete the downstream catalyst monitor in the PCM, (good luck) that will keep the light off.

This is straight from the GM shop manual P0420 flow chart:

"CIRCUIT DESCRIPTION
This diagnostic test is designed in order to measure the efficiency of the Three-way Catalytic Converter (TWC) system. Catalytic convertor efficiency is a measure of its ability to store oxygen after converting the levels of Hydrocarbon (HC) , Carbon Monoxide (CO) , and Oxides Of Nitrogen (NOx) to less harmful gases. The control module is able to evaluate the catalyst efficiency once the vehicle has met the enable criteria and the vehicle is at idle instead of the steady cruise speeds used in the past. Once the conditions for running this Diagnostic Trouble Code (DTC) are met, the control module commands either a lean or rich air/fuel ratio depending on the current state of the exhaust oxygen level. The control module issues a rich command if the exhaust is currently lean, or a lean command if the exhaust is currently rich. After completion of the first command, a second and opposite command is issued.

For example, if the control module were to command a rich mixture, the upstream Heated Oxygen Sensor (HO2S) voltage would increase immediately. The rich mixture is delayed in reaching the downstream HO2S due to the conversion process occurring within the converter. The higher the efficiency, the more the delay before the rich or lean mixture is detected by the downstream Oxygen (O2) sensor. As a result of the lower conversion efficiency within a damaged or poisoned catalyst, the delay in the rich or lean mixture reaching the downstream O2 sensor is significantly shorter. This DTC monitors the amount of time required for both the upstream and downstream HO2S voltages to cross a calibrated voltage threshold in response to the rich or lean command."
 
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Old 08-08-2013, 12:10 AM
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That's very interesting... Hmm... Maybe I can find someone to do some math for me and do some wiring work. LOL
 

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