Fuel economy prob with cat del but rear o2's installed

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robustRed
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Joined: Tue Apr 26, 2011 11:12 pm

Fuel economy prob with cat del but rear o2's installed

Post by robustRed »

I will start by saying that my signature is outdated lol. I'm currently in a 2015 SRT 6.4 Challenger 6 speed and only modifications done are catless mid pipes (checked several times for leaks, with and without smoke. Found zero leaks.) And a custom tune via a very reputable tuner out of the DFW area. Some may know him as Jay. To my knowledge he's done everything right for such a simple modification.

The issue is poor(ish) fuel economy. Now I know the government is doing crap with mixing in more ethanol with regular gasoline but I started having the issue 3 years ago when I put the pipes on. The tuner had told me that since (and don't quote me here, I'm trying to remember a conversation we had 3 years ago) the cars PCM was designed a certain way, that the PCM could basically be told the car never had rear o2 sensors ever installed. Too which I was told I could unplug them and all would work as it did. Long of the short is, I never got around to unplugging them since I did not have extra bung plugs and did not want wires zip tied under the car. Now even though the car will pass a Texas emissions test just fine (with the test reading the rear o2 sensors as "not supported") I still get fuel trims from those sensors and from time to time bank 2 rear sensor will be moving back and forth just like the front, it will all of the sudden jump instantly to +25% - +29% (or negative. It's been a while since I logged a file on it) but the bank 1 sensor 1 will start slowly adjusting and adding more and more fuel until it reaches a random number between 9% and 15% (or when I look at voltage it locks in a specific random voltage and will not change for several miles, then it'll start adjusting again because it's too rich and goes well into the negatives before returning to normal function). My question is, is leaving the rear sensors installed and hooked up still giving the PCM data and adjusting based off of that? And should I unplug them to see if the issue resolves? I have replaced sensors (purely based on speculation) and done injector duty cycle tests and leakage tests as well as checked for vacuum leaks and evap leaks and everything checks out 100%. I'm curious if I'm overthinking this or if I just need to remove the rear sensors. Any advice is welcome. Thanks. And just to note when the pipes were replaced the economy dropped an average of 2.5mpg driving the same trip everyday for years.
2008 5.7L Ram 1500 QC*Spartan Plus cam* Ported Heads*LT headers*E-Fan*Custom Tune*and 4.56s out back* 341rwhp/341rwtq with 105 ambient air temp!
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