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2008 chevy trailblazer_ss_3ss
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Discussion Starter #1
I just put some pacesetter catless longtube headers on my 2008 trailblazer SS. The headers were only drilled out for the rear o2 sensors, not the front. With catless longtube headers, are the front o2 sensors necessary or will I be ok with the mass airflow sensor? I don't want to blow anything up! Sorry if I'm posting a repeat question, but I didn't find anything using the search. Thanks
 

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2007 chevy trailblazer_ss_3ss
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Need both

You will get codes with or without the sensors I'd be surprised if it ran worth a crap, unless you have a tuner that turns rear sensors off. But you need both upstream and downstream sensors, again unless you turned rear sensors off. You can buy O2 simulators that are mini catalytic convertors for the rear sensors
 

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2003 gmc envoy_slt
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The location for the front O2s are in the collector. This is where the most heat is generated. This will likely be farther back then they when with the OEM manifolds.

Yes you need the front O2s, you will pay for it in lost performance and MPG with no front O2s.

The rear O2s, as suggested, use anti-fouling adapters (O2 simulators), under 20 bucks.
Their are a few different depths, be sure the ones you buy are deep enough for your O2s. Take a measurement.
 
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