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  #1  
Old April 16th, 2016, 07:04 PM
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Robert Ragland
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Running without cats.

I've searched this issue and can't find a consensus. Saw an off-road truck with straight pipes.

If the 3.9 runs without the converters, does the ECU accept the reduced back pressure? Does the truck run fine, or does it require the non-cat wiring? I've read some trucks had specific tune resistors while others had universal wiring.

TIA
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  #2  
Old April 16th, 2016, 08:28 PM
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Theoretically you need to change the tune resistor.
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Old April 16th, 2016, 08:36 PM
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Robert Ragland
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That's what I told this person.
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Old April 16th, 2016, 08:46 PM
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They smell like raw fuel badly without cats. I assume a tune resistor fixes this but I don't know.
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Old April 16th, 2016, 09:25 PM
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I'm running a 3.9 without cats, but still have o2 sensors. Haven't noticed any smells or change in performance. Occasionally get a code 48, but that was occurring since I bought the thing 5 years ago.
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Old April 16th, 2016, 10:07 PM
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Chris
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O2 sensors are pre cat on 95 and prior. So if legal, I don't think it should matter. As for smell, something else was going on.
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Old April 17th, 2016, 06:22 PM
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no need for cats, makes your truck much louder. yes tune resistor and adjust the MAF. good luck with the tune resistor.
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