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So about a week ago I installed the zzp catless downpipe and the catted midpipe combo. No lights went on and it drove fine for that week. I started the car one morning and I heard a difference in the sound. While driving the check engine like came on. I got it scanned and it was the P0420 code. The car seemed to drive a little different. Seems to be the car doesn't want to push and the rpms don't go past 4K. I did not get a tune for the downpipe and midpipe. Not sure if the BNR tune will help this problem or just get rid of the light. HELP!
 

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P0420 shouldn't give you any drivability issues. It's just an emissions code.
 

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P0420 shouldn't give you any drivability issues. It's just an emissions code.
No, it's because the O2 sensor isn't reading right. That sensor is what controls his or her fueling. It thinks a cat should be there, and there isn't, so it's skewed.
 

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The O2 sensor is reading right its the emission code that isnt happy.
 

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Hence getting the p0420 code. Car just won't pass emissions test.
 

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What the Home Mechanic Needs to Know about O2 Sensors

"The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture. It tells the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen)."

It's now sensing incorrectly, because the cat is no longer there, and it's getting readings that are not expected. That's why it's running poorly.
 

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I promise I understand it's just an emissions code, but with how sensitive these cars are to the slightest change electronically, it really shouldn't come as a surprise that this is the issue. Was running fine, changed parts without the required tuning and got CEL, not running fine. We can see where the issue is.
 

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Dude! I watch the voltage readings of the primary and secondary sensors, and a tune is def needed to run a catless setup off the primary. I've only been able to trick the O2 sensors on N/A cars by extending the bung or extending the sensor distance from the engine. FI cars need dem toonages, can't trick them at all! LOL!
 

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Not sure if a trifecta tune is setup to run catless DP from the original tune. Ive never had the select-a-tune from trifecta changed and when I ordered it I was running stock filter box and both cats. I changed to a CAI and DP with no retune or ill effect other than getting P0420 occasionally. The code only triggers when Im idle in gear at a red light for too long. If I shift to neutral at red lights I never get the code. Even when code is triggered I can run in performance or eco tune with no drivability issues whatsoever.
The sensor is still reading the air/fuel ratio and doing its job. Its just outside the "happy perimeters" of the emmisions. The cat is only reducing the toxicity of gases to save on emmisions.
 

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Not sure if a trifecta tune is setup to run catless DP from the original tune. Ive never had the select-a-tune from trifecta changed and when I ordered it I was running stock filter box and both cats. I changed to a CAI and DP with no retune or ill effect other than getting P0420 occasionally. The code only triggers when Im idle in gear at a red light for too long. If I shift to neutral at red lights I never get the code. Even when code is triggered I can run in performance or eco tune with no drivability issues whatsoever.
The sensor is still reading the air/fuel ratio and doing its job. Its just outside the "happy perimeters" of the emmisions. The cat is only reducing the toxicity of gases to save on emmisions.
You're tuned. It's not comparable. The cat is not only reducing the toxicity of gasses, it's a restriction in the exhaust; the largest restriction at that.
 
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