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Thread: help with P0420 please

  1. #1
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    Default help with P0420 please

    after reprogramming the wifes trailblazer with the the tune i listed on another thread in this forum, i finally got around to putting the cold-air K&N intake in and redoing the exhaust.

    i cut out the cat & everything behind it (there were some nasty crimps in the tailpipe). i then replaced everything with 3" including a 3" magnaflow muffler.(the post cat O2 sensor is still wired up and in place)
    Sounds awesome (the wife hates it & i will be adding a 3" resonator where the cat used to be to bring down some of the in-cab drone)

    I thought i had turned off all the switching in the first tune to eliminate any codes thrown by removing the cat, but i guess not.

    i keep getting P0420 codes, what am i missing????

    here is my latest tune
    Attached Files Attached Files

  2. #2
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    Ill look at it later tonight when I have a few mins. Why are you using the post-cat O2 without a CAT? Its not going to do anything AFAIK without a cat being there... And you are going to want to play with spark and camshaft settings with that exhaust, believe me I had a 3" catback and lost a ton of low-end tq which we already have too little of. Got the Magnaflow catback and got all my power back without changing anything in my tune.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, bone stock (for now...)
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

    New site! SE22 Performance Custom Tuning

  3. #3
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    i realize the post cat O2 wont do anything, but i was worried that disconnecting it would throw its own set of codes. it was easier to just leave it where it was.

  4. #4
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    Well you didnt have P0420 turned off in the DTC Enable/Disable section, I turned it off plus another post cat O2 thing. That might help a little bit.

    I changed a few other things that you might like, compare this one Im updating to the one you uploaded and see if you like the changes. Some like TCC PWM I havent had a chance to check, but other than that the changes are very nice.
    Attached Files Attached Files
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, bone stock (for now...)
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

    New site! SE22 Performance Custom Tuning

  5. #5
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    ahh, thanks for the help
    i see which ones i missed now.
    everything looks good with the changes you made from what i can tell. ill try to get this new tune uploaded sat. Hopefully ill be able to do some logging & post my results.

    i did some logging today and compared it to a log i did before the intake & exhaust changes. Just at a glance it looks like its probably running a little lean now, the knock retard is pulling more timing & more often than before. Im thinking of doing a +2% increase across the board to the VE tables to up the fueling a little. Ill probably do some runs with the wideband O2 later on.

  6. #6
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    No prob man, Im just happy to help. Dont know much about other engines and cant really do much besides general changes for anything but the LL8.

    Id go ahead and do that VE change, exhaust+CAI means you should be running a little leaner from the extra air from the CAI. I wish there was a way to desensitize the knock sensors, with no cat and 3" all the way back you are probably getting a bunch of false knock.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, bone stock (for now...)
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

    New site! SE22 Performance Custom Tuning

  7. #7
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    here is my latest tune & log file.
    the transmission feels better with the changes you made.
    I increased the VE tables 2% @ 1300rpm+ & 30%+ load(my initial adjustment right across the board was giving some problems)
    I also pulled some timing out of the spark tables just in the trouble areas.
    Attached Files Attached Files

  8. #8
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    Glad to hear you like it, you'd like the trans a ton better if you got a Vette servo in there as well. Mine shifts so firm now, I had to actually lower the 1-2 base pressure by about 10% because it was snapping my neck.

    Those changes look good, if your engine likes it thats what counts. Every one is a little bit different. Does look like in that log that you're getting a bit of KR when you get into PE mode. Im pretty sure I get some too, havent figured out why yet. Here in a few weeks Ill be able to better figure that out.

    Are you still getting the P0420 code now?
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, bone stock (for now...)
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

    New site! SE22 Performance Custom Tuning

  9. #9
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    well, it set another P0420 code today :(
    im going to go through all 3 diagnostic menus again from top to bottom and see if theres anything i can turn off in reference to O2 sensor 2

  10. #10
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    Hmmm, weird. Ill look through your tune again and see if there's something I missed as well..

    Edit:
    Theres
    P0054 "HO2S Heater Resistance Bank 1 Sensor 2"
    under DTC Enable/Disable that you might want to change to "Not Reported", but other than this one thats all I see thats is related to the Bank 2 O2 sensor that isnt already turned off.
    Last edited by ScarabEpic22; April 28th, 2008 at 12:13 PM.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, bone stock (for now...)
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

    New site! SE22 Performance Custom Tuning

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