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Advice on misfire?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by BuyJapanese, Mar 7, 2022.

  1. BuyJapanese

    BuyJapanese Member

    Joined:
    Jun 12, 2019
    62
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    Location:
    Wisconsin
    Vehicle:
    2005 Prius
    Model:
    II
    I recently picked up a 2007 with 230k miles. Intermittent misfire, typically just on cold startup. Sometimes I notice a slight roughness, and sometimes it feels like one cylinder is missing 100% of the time.

    The codes I get are P0300 and P0301.

    I replaced the spark plugs, no difference. Redline, seafoam, no difference.

    I then moved cylinder 1 fuel injector to cylinder 2, cylinder 1 ignition coil to cylinder 3, and cylinder 1 spark plug to cylinder 4. No difference, still P0300+P0301, and the misfire disappears when I tap the gas.

    MAF is newer, I cleaned it, non-OEM.

    Compression readings may be helpful: 120 on 1, 130 on 2, 140 on 3 and 4. So that's a problem. My method for that was to put the car in inspection mode (ready-gas-gas-neutral-gas-gas-park-gas-gas) and then hold start for 5 seconds to crank it.

    So...what should I be looking for here? Head gasket or worn valves/rings? I have no other symptoms of a bad head gasket. Anyway, if it's at that level I'm just going to keep driving it as-is because it runs fine when I hit the gas. But am I missing something simpler? For instance, I was wondering if the intake gasket could be the problem with a leak around cylinder 1. But the bad compression readings point me in a different direction.

    Should I replace the intake gasket just in case? Not very hard...
    Should I put some UV leak tester dye in the oil to see if the head has a micro crack?
    Any other suggestions?

    Thanks in advance!