8.1 Big Block O2 sensors

RDomeck

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Feb 18, 2020
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Hello, Just purchased an 03 with an 8.1 and an Allison transmission. Someone has installed headers, deleted the cats and installed a 4" flow through muffler. You can not imagine how obnoxious this thing sounded. I have installed a big 50 series Flowmaster and it is much more tolerable. I am planning on installing the cats back on it for two reasons. I care a little bit about our planet and it could stand to be a little quieter still. When looking under it for a good while, I can not find the post converter O2 sensors.

I plugged in my scanner and it shows that it is reading something from those sensor's, but it also shows at the bottom that it is running OBD1. This seems really odd to me, but who know what some idiot has done before I purchased it.

Anyone have any experience with this year of truck to know if it should have 4 sensors? Any idea how far back they should be? My 1999 3/4 Big Block Suburban has them pretty far back.

Pretty good running truck, but mileage seems to be averaging around 8. I think that could get a little better too.
 

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