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Thread: Knocking at WOT...is it headers?

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    Default Knocking at WOT...is it headers?

    I just recently got headers for my truck and it has been shifting fine for a month until now. When ever im on the hwy at 70 mph i hear this knocking noise that i never heard before. It sounds like a train on the train tracks going fast and its scaring the daylights out of me.

    The knocking ocurs at 70 mph, but before or after there is no knocking. Off the line from stop to go, it feels like the truck has lost some power. Ive change the tune to stock and its still the same.

    Had recently changed coil and spark plugs, cleaned throttle body but that was a year ago.

    Here is the data that i recorded maybe you can check it out and maybe help me solve this problem. Thanks

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    Missfire.efi
    TCC Lock Up On 4th_0001.tun
    2002 4.2L I6 Trailblazer LTZ

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    do you think its the header that causes this?
    2002 4.2L I6 Trailblazer LTZ

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    Joe (Moderator) joecar's Avatar
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    GB,

    I had a quick glance at your log file, I see you have several problems:
    - long tube headers and exhaust plumbing may be hitting the chassis at 70 mph;
    - detonation/knock is present below 70 mph, see next points;
    - one NBO2 is not functioning, it flatlines at zero volts, sounds like it's shorted to ground;
    - you may be running a bit lean, this may be causing detonation.

    When you hear the knocking noise:
    - if it sounds like rapidly popping corn from the front during load, it may be detonation;
    - if it sounds like banging under the floor panels it's the headers or merge pipe hitting;

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    yeah it sounds like pop corn/train noise.

    So how do i make it more richer? And what does NB on NBo2 mean dince i had both o2 sensor replace and installed a spacer on the rear o2?
    2002 4.2L I6 Trailblazer LTZ

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    ?????
    2002 4.2L I6 Trailblazer LTZ

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    Joe (Moderator) joecar's Avatar
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    HO2S21 shows zero volts thru out the whole log.

    (HO2S21 is bank2, sensor 1... i.e. front O2 sensor on the RHS)

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    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by goldbergv95 View Post
    ...
    So how do i make it more richer? And what does NB on NBo2 mean dince i had both o2 sensor replace and installed a spacer on the rear o2?
    Actually, I previously glanced at your log file too quickly, and now I had a closer look, so ignore my comment about being lean...

    the KR seen in your log looks strange (strange shape to the waveforms, and very long duration, and the engine load does not appear to be large)...

    I can't tell if it is real knock or other noise... your log shows 1.1 seconds between frames (meaning 90% of the possible data points have not been recorded)... can you reduce the pid count (no more than 24 pids) and make sure the logging mode is Stream-Fast.

    Bank 1 LTFT is correcting by an average of -3.9% (which means you're not lean, the trim is removing fuel to maintain stoich).

    Bank 2 has zero O2 voltage (indicates a possible short to ground)... you have to get this fixed before doing anything else.

    Can you inspect the headers and exhaust system for contact with anything...

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    Quote Originally Posted by joecar View Post
    Actually, I previously glanced at your log file too quickly, and now I had a closer look, so ignore my comment about being lean...

    the KR seen in your log looks strange (strange shape to the waveforms, and very long duration, and the engine load does not appear to be large)...

    I can't tell if it is real knock or other noise... your log shows 1.1 seconds between frames (meaning 90% of the possible data points have not been recorded)... can you reduce the pid count (no more than 24 pids) and make sure the logging mode is Stream-Fast.

    Bank 1 LTFT is correcting by an average of -3.9% (which means you're not lean, the trim is removing fuel to maintain stoich).

    Bank 2 has zero O2 voltage (indicates a possible short to ground)... you have to get this fixed before doing anything else.

    Can you inspect the headers and exhaust system for contact with anything...

    But for the rear O2 we installed the o2 spacer that prevents the P0420 from popping out but as you can see on my engine light diag. it still pops out. This is an example, we only install just one spacer. Maybe ill have to remove this spacer...




    Yeah, we had a big blizzard around the DMV area. Hardly every happens where i live until now, which is why i had slow drives. Ill make another log after tonights bigger blizzard. THanks
    2002 4.2L I6 Trailblazer LTZ

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    Joe (Moderator) joecar's Avatar
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    Is the O2 sensor hitting the heat shield...?

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    Quote Originally Posted by joecar View Post
    Is the O2 sensor hitting the heat shield...?
    No that picture above is not mine. Just an example. But to let you know the rear oxygen sensor is on the left side of the pipe (when look forward towards the engine) pointed towards the direction of the transmission. So not its not near the heat shield.

    2002 4.2L I6 Trailblazer LTZ

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