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Discussion Starter #1
I have a 2008 Avenger sxt 2.7L
I installed a few years back an after market exhaust, a flow master I believe. I also removed the resonator. Since then, i get a couple o2 sensor codes showing up on my check engine light. Any idea on where to go from here? I hate living with that CIL on all the time, can i flash the ecu some how, take it somewhere? I dont know which oxygen sensors its exactly causing the code yet. For anyone wanting to put an aftermarket exhaust on though, do it! It increased mpg by 5-6 across the board. Im also looking to put a cold air intake on the car, any ideas? Does the K&N for the 3.5 work? Will putting a CAI cause me issues to where i need to tune it or anything? Thank you
 

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How many miles on the car and how long after doing the exhaust before the CEL started coming on?
In theory of operation you could have NO exhaust piping AFTER the rearmost O2 sensor/cat and it would not affect readings to throw the CEL.
My opinion is it's not your aftermarket exhaust but some other problem further forward with the 2.7 motor, they were known for converter and EGR into exhaust manifold concerns.
Posting the specific code(s) here will gain you better help.
 

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The car has 62k miles. I put the exhaust on about 3 years ago along with removing the resonator, As far as I remember it came on within a month of running it with the exhaust. After reseting the light, it comes on after about 5-10min of driving
 

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How many miles on the car and how long after doing the exhaust before the CEL started coming on?
In theory of operation you could have NO exhaust piping AFTER the rearmost O2 sensor/cat and it would not affect readings to throw the CEL.
My opinion is it's not your aftermarket exhaust but some other problem further forward with the 2.7 motor, they were known for converter and EGR into exhaust manifold concerns.
Posting the specific code(s) here will gain you better help.
I will post the codes soon
 

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Discussion Starter #6
How many miles on the car and how long after doing the exhaust before the CEL started coming on?
In theory of operation you could have NO exhaust piping AFTER the rearmost O2 sensor/cat and it would not affect readings to throw the CEL.
My opinion is it's not your aftermarket exhaust but some other problem further forward with the 2.7 motor, they were known for converter and EGR into exhaust manifold concerns.
Posting the specific code(s) here will gain you better help.
P0420 and P0430 are the codes been thrown
 

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Run a tank with a can of Seafoam added. It will clean out any foreign substances from the exhaust that may be causing the issues. It cleans from the engine thru the catalytic converter and sensors.
 

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Run a tank with a can of Seafoam added. It will clean out any foreign substances from the exhaust that may be causing the issues. It cleans from the engine thru the catalytic converter and sensors.
Ill try that tonight. Ive been clearing the code every time it throws, since it wont let me remote start my car with a CIL , which it takes about a couple days or 3 hours of driving for the CIL to come back on after i clear it.
 

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Agreed about the Seafoam as a first attempt.
A lot of old threads on the forum relating to these codes and the 2.7 motor. They are rather finicky about throwing these codes.
Also, do you do mostly very short drives with the car? A good LONG at highway speed run is needed to heat the cats fully and burn off the substrate in the converters.
IF you have a scanner with live data capability, you could monitor converter temps and fuel trims. to help figure out what's going on.
 

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Discussion Starter #10
Agreed about the Seafoam as a first attempt.
A lot of old threads on the forum relating to these codes and the 2.7 motor. They are rather finicky about throwing these codes.
Also, do you do mostly very short drives with the car? A good LONG at highway speed run is needed to heat the cats fully and burn off the substrate in the converters.
IF you have a scanner with live data capability, you could monitor converter temps and fuel trims. to help figure out what's going on.
20min drive to work on the highway. The cats get up to 1500 degrees, i have a blue tooth scanner and monitor temps and such. I put seafoam in last night will see how that does. I believe that it is both sensors after the cats on the down pipes. Sense i did aftermarket exhaust I believe there is little to no back pressure in the pipe, allowing the air inside to be less dense? So then trigging the system that the cats aren’t doing the correct thing
 

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Are these still the original "downstream" 02 sensors or have they been replaced with aftermarket ones?
 

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Discussion Starter #13
Agreed about the Seafoam as a first attempt.
A lot of old threads on the forum relating to these codes and the 2.7 motor. They are rather finicky about throwing these codes.
Also, do you do mostly very short drives with the car? A good LONG at highway speed run is needed to heat the cats fully and burn off the substrate in the converters.
IF you have a scanner with live data capability, you could monitor converter temps and fuel trims. to help figure out what's going on.
Tried the seafoam, the codes still went back off, tried reseting the light several times, stills come back after driving for a bit
 
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