4 Cat system
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New User
Joined: Aug 2009
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From: Oregon
4 Cat system
My ? is has any one replace the 4 cat system with a 2 cat system?
one cat is bad and iam just whant to redo hole system instead off the 4 cat system like to do 2,has anyone done this and have emissons work?
one cat is bad and iam just whant to redo hole system instead off the 4 cat system like to do 2,has anyone done this and have emissons work?
Elder User
Joined: Oct 2010
Posts: 602
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From: Maryland
I just replaced my entire system and very happy with the results on my 4.2 truck. Shorty headers, magnaflow direct fit cats, a glasspack muffler and all new 2.5" oem style pipes. Replaced all 4 o2 sensors since they had to be removed anyway.
Someone else said ee have 4 cats becaust the rear cats have to reach a certain temperature or the o2 sensors will give a rich/lean reading.
Someone else said ee have 4 cats becaust the rear cats have to reach a certain temperature or the o2 sensors will give a rich/lean reading.
Lead Driver
Joined: Sep 2006
Posts: 7,907
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The rear cats do have to heat up and all OX sensors have to reach about 600 degrees to output the response to Oxygen content.
Both front and rear Ox sensors have heaters but they are employed mainly to help the whole system to get all parts up to temperature close to the same time interval from cold starts.
It's just not a matter of removing them because they are part of an Engineered operation system you will be altering.
The rear sensors have nothing to do with mixture control.
The rear sensors are there to report the Ox storage ability and health of both cats on each side. This function has a number of codes assigned for failures detected.
Only the front sensors report for mixture control. They are ahead of the cats and have no direct relation to them except how rich or lean the exhaust Ox content is before it ever gets to the first cat.
Rich or Lean means how much Oxygen is detected in the exhaust. That's what they do.
Good luck.
Both front and rear Ox sensors have heaters but they are employed mainly to help the whole system to get all parts up to temperature close to the same time interval from cold starts.
It's just not a matter of removing them because they are part of an Engineered operation system you will be altering.
The rear sensors have nothing to do with mixture control.
The rear sensors are there to report the Ox storage ability and health of both cats on each side. This function has a number of codes assigned for failures detected.
Only the front sensors report for mixture control. They are ahead of the cats and have no direct relation to them except how rich or lean the exhaust Ox content is before it ever gets to the first cat.
Rich or Lean means how much Oxygen is detected in the exhaust. That's what they do.
Good luck.
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New User
Joined: Aug 2009
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From: Oregon
Blue i get all that. I work on this stuff all day long. so your saying that o2 in the rear can tell if there only one cat verses 2 have you tried it? thats my ? Not looking for any kind of advantage .
Elder User
Joined: Oct 2010
Posts: 602
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From: Maryland
Mine is a 2004 Heritage edition, basically a 2003 sold as a 2004. Same 4.2 V-6 and all. Yes, it passed with no issue. I used Bosch o2 sensors up front and NTK sensors for the rear. From my experience with these trucks and using computer tuning software that combination worked the best.
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