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Just bought a 2015 Challenger SRT Scat Pack with 26,000 miles. Car is immaculate and the 1st owner did many mods. My question is I recently bottomed out because car sit very low and our roads suck in Illinois. Didn’t hit too hard but enough that I started throwing codes for O2 sensors because they scraped going over tracks. I replaced both downstream with Bosch because they didn’t have the Denso or NTK in stock. After that I started throwing codes for upstream sensor responding slowly And replaced those with Bosch (all 4 are narrowband exact replacement) Problem now is that when I start car from a cold start it idles really high and throws a running lean code if I let it idle itself down. (If I hit the gas it will idle down quick and not throw a code) The exhaust has been changed to flowmaster and not sure of the headers. My question though is I removed a 3” extender on both downstream mounts on the exhaust to make them sit higher and not so low but I have been reading on here that when modifying exhaust that maybe needed for response time. Any thoughts on this would be helpful. I am thinking I should put them back on before ordering the Denso‘s.
 

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Just bought a 2015 Challenger SRT Scat Pack with 26,000 miles. Car is immaculate and the 1st owner did many mods. My question is I recently bottomed out because car sit very low and our roads suck in Illinois. Didn’t hit too hard but enough that I started throwing codes for O2 sensors because they scraped going over tracks. I replaced both downstream with Bosch because they didn’t have the Denso or NTK in stock. After that I started throwing codes for upstream sensor responding slowly And replaced those with Bosch (all 4 are narrowband exact replacement) Problem now is that when I start car from a cold start it idles really high and throws a running lean code if I let it idle itself down. (If I hit the gas it will idle down quick and not throw a code) The exhaust has been changed to flowmaster and not sure of the headers. My question though is I removed a 3” extender on both downstream mounts on the exhaust to make them sit higher and not so low but I have been reading on here that when modifying exhaust that maybe needed for response time. Any thoughts on this would be helpful. I am thinking I should put them back on before ordering the Denso‘s.
If you bottomed out the car there's a chance you dislodged the exhaust and there are now exhaust leaks which can affect the O2 sensors.

Then you have changed the exhaust. Even if you bolted everything back up and did not introduce any exhaust leaks changing the exhaust can affect exhaust gas flow and it may no longer be optimum and the O2 sensors downstream (or possibly even upstream) of the change are no longer in the sweet part of the exhaust gas flow.

I would restore the exhaust back to its original configuration. I'm talking about the aftermarket system and the 3" extenders you removed. Prior to the bottoming I believe the system was working just fine.

The high idle speed and error code indicate the engine is running lean. Normally one would suspect an intake air leak. It is possible the bottoming out may have also affected the intake system. The bottoming out can be quite violent. (Years and I mean years ago, in my Dad's Bel Aire on an unfamiliar road I encountered a rise in the road and after the rise the car bottomed out hard to enough to break the cast iron exhaust manifolds.)

But improper O2 sensor operation could also be to blame. The replacement sensors can be suspect. For every person who uses any old O2 sensor as a replacement and reports perfection there's another person who has nothing but trouble with any O2 senors other than factory OE sensors. Whenever I have replaced O2 sensors I have done so using OE sensors, except in one case where the tech said the OEM Bosch units were the same as the OE Bosch units sold by the factory. I had him install the OEM Bosch sensors this at 132K miles. At 161K miles when I got rid of the car the sensors were fine but my preference is still to stick with the OE sensors.

Before you trash the new sensors though restore the extenders. Be sure the exhaust is leak free. Check for air intake leaks. Can the Scat Pack engine suffer from loose intake fasteners like I believe the 5.7l engine does?
 

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I have heard bosch sensors can cause issues. Go to rock auto and get ntk. They make the oem ones. Worth a try

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Thanks guys! I am gonna put the extenders back on tonight and check for leaks before taking all 4 Bosch back. If problem consists I am gonna go back to NTK’s to go back to OEM. I will let you guys know.
 
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