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2012 Prius - Cylinder 4 Clunk

Discussion in 'Gen 3 Prius Main Forum' started by sj-prius, Oct 3, 2023.

  1. sj-prius

    sj-prius Junior Member

    Joined:
    Dec 7, 2022
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    Location:
    san jose, ca
    Vehicle:
    2012 Prius
    Model:
    II
    Kind of a long story, but I recently did the head gasket in my 2012 prius. The headgasket showed signs of being compromised for cylinder #3 where coolant was getting in. The head gasket visually showed signed it was compromised at cylinder #3. Everything is reassembled, but it makes a weird clunk sound. Unplugging different coils led to the issue being isolated to cylinder 4. The engine runs fine if the coil for cylinder 4 is unplugged. Prior to the repair, cylinder #4 did not have any issues.

    Below is a list of stuff I've tried so far -
    - compression test, all cylinders are 170psi +
    - swapping coils, sparkplugs, injectors with other cylinders to #4.
    - reset the computer by unplugging the battery
    - checked the timing. The timing marks line up for the two cams and cylinder 1 is in in the upmost position by putting a stick down the cylinder to measure
    - Put a camera down all cylinders and the intake valve section, they seem normal
    - Turned the crankshaft by hand and it rotates fine without abnormal sounds
    - When the engine cranks when the electric motor runs, there are no sounds, appears to be normal.

    There are a number of CEL codes -
    P0031 - Heated o2 sensor
    P0102 - maf sensor
    P011 - intake air sensor
    P0351, P0352, P0353, P0354 - coils were unplugged/removed for the compression test
    P0403 - EGR

    The CEL codes appear to be from unplugging and re-plugging various sensors/devices. Pressing the gas pedal while in park does not rev the engine.

    Any thoughts?