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Header-back exhaust

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by AKRide907, Jul 23, 2012.

  1. AKRide907

    AKRide907 Rockstar

    So ive been doing some research online now and ive talked to a few mechanics, and the responses ive gotten are pretty mixed on this subject.

    Im looking to do a complete redo of my exhaust system. Mostly cause its all rusted out. Ive already got some long tube headers on the way in the mail. The real interesting part is here: The 02 sensors. I know for a fact that engine and the computer DO need the pre-cat 02 sensors so that it can constantly adjust the air/fuel mixture. So ill be putting the pre-cat 02 sensors into the new pipes for sure. That leaves the post-cat 02 sensors. How necessary are they. Ive had a mechanic tell me that they are really only put in place to make sure that the cats themselves are working. They dont do anything for the engine. How true is that? Alaska doesnt have any emissions testing and i dont plan on taking my truck out of state any time soon, so if i can just drop the cats out of this i would be pretty happy. But i want to be sure about it though. Does anybody know anything pertaining to post-cast 02 sensor functionality?

    Thanks!!
  2. dbb06

    dbb06 Member

    I can't say for sure, though I doubt it would have any effect on the engine. I have know people running without cats and not had any problems. I think they ran a bypass or something for the rear sensors so they wouldn't have the check engine light come on. Some tuners allow you to shut off the rear sensors as well. I had a 96 t-bird with a gutted cat and it never had any problems but I can't remember if it had an after cat sensor or not.
  3. nancygrl

    nancygrl New Member

    I can tell you from what I learned from doing longtube headers on my 2011 Camaro SS. If you're gonna install longtubes, then to get the most out of them (performance and efficiency) then you'll want to get a tune. The mechanic is correct that they're there to tell the ECU that the cat is working correctly. But with the LT's the sensors are further away and the temps won't register right. Have your tuner program the ECU for the rear O2 sensors to "not reporting", that way you don't get the dreaded check engine light.

    I tried to fool the ECU with O2 extenders/bypass whatever you want to call it, and it didn't work. The check engine light still came on. It took a little longer, but still came on (300 miles of driving vs. 100 miles). If you're gonna have it tuned then it won't take much to program the ecu vs. jury-rigging something and hope to keep the check engine light off.
    Last edited: Jul 27, 2012

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