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Gen 3 Misfire P0303 Denso Plugs

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by High Mileage, Feb 1, 2019.

  1. High Mileage

    High Mileage Active Member

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    Started getting a light misfire under hard acceleration several days ago. Yea I know its a prius and I really don't get too aggressive with it most of the time. Felt the misfire and also got the flashing CEL for a few seconds each time. I'm at 262K miles and I last changed the plugs at 192K so I had not expected a problem so soon. I ordered a new set of Denso SC20HR11 Iridium plugs which were the stock plugs that I installed at 192K miles. I got the wiper and cowl assembly out in about 10 minutes, and had the plugs out in another 5 minutes. I was surprised to find the center electrode of all the plugs completely gone. The gap was well over .080, new they are supposed to be .043. I put in the new plugs and also did an intake EGR clean. EGR ports were still very clean compared to when I did the cleaning at 192K.
    Reading some other posts I wish I had purchased the Denso (4711) IXEH20TT since they are supposed to be double iridium, I will get them next time around.
    Not sure if the previous set I got were counterfeit or something. I still stand behind Denso and NGK brands. This post is just to help someone out in the future.
     

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    #1 High Mileage, Feb 1, 2019
  2. High Mileage

    High Mileage Active Member

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    Correction: Amazon details says Denso (4711) IXEH20TT and Denso 3444, center electrodes are iridium, grounds are platinum. I'm confused now. Oh well nothing new there.
     
    #2 High Mileage, Feb 1, 2019
  3. JC91006

    JC91006 Senior Member

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    Your old plugs look to be different than your new plugs. Maybe the old ones were not the correct part?

    Anyways hope that solves your problem
     
    #3 JC91006, Feb 2, 2019
    Raytheeagle and Mendel Leisk like this.
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    FWIW, Denso/Toyota have replaced the SC20HR11 with SC16HR11, which is slightly hotter.
     
    #4 Mendel Leisk, Feb 2, 2019
  5. JC91006

    JC91006 Senior Member

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    Why the hotter plugs?
     
    #5 JC91006, Feb 2, 2019
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    I'd guess they're finding more deposits than they liked, say dealerships reporting? I'd suspect it's only a slight difference. Apparently if you go looking for the 20's you're redirected to the 16's??

    There's a past thread here somewhere on it, somewhere. Ah here:

    Gen 3 Prius Spark Plugs superceded with hotter plugs | PriusChat
     
    #6 Mendel Leisk, Feb 2, 2019
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  7. High Mileage

    High Mileage Active Member

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    JC91006, same exact plug at least by the part number. Denso SC20HR11. Maybe the angle and fact that the center electrode is gone make it look different. It definitely fixed the issue. If my yearly miles driven stay the same I should know in about 2 years if these last longer or not.:)
     
    #7 High Mileage, Feb 2, 2019
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  8. JC91006

    JC91006 Senior Member

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    The tip on your picture looks like a platinum tip on the old plugs. New one looks like the proper iridium tip. Strange the part number would be the same on the plug.
     
    #8 JC91006, Feb 2, 2019
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