Misfire troubles

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Partygoat, Jan 4, 2025 at 3:20 PM.

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  1. Partygoat

    Partygoat New Member

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    2010 Prius
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    So it started out running good, around 260K miles. Then it started missing a LOT, it was undrivable. So the first thing I did was replace the sparkplugs, this made it run better, but the issue came back. I checked my codes and it said misfire on cylinder 3 so I replaced the cylinder 3 coil pack. This fixed the issues for about 10 miles, then it started missing just as bad as before and my codes came back as cylinder 1,3 and random. After that I took the EGR valve and cooler out. They were very clogged. When I cleaned them the cleaning solution only trickled through, but by the end I got it flowing much better. So I put it back together yesterday and took it on a 20 mile test drive, it had no issues. Today when we took it out it started missing after about 20 minutes of running when the engine was starting up. It was only like 1-2 seconds of running rough. What should I look at next if it gets worse? Should I just roll with it till it gets worse then try something else? I was looking at replacing the motor, is that worth it with 3rd Gen Priuses?

    Sorry for the rambling and thanks for any help.

    Also my fuel mileage has been about 38MPG
     
    #1 Partygoat, Jan 4, 2025 at 3:20 PM
    Last edited by a moderator: Jan 4, 2025 at 7:51 PM
  2. BiomedO1

    BiomedO1 Senior Member

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    Replace the head gasket ASAP. You've got an intermittent seepage. This can be verified by placing a bore scope down the spark plug hole and looking at the top of the pistons. They should be pitch black across all 4, any pistons tops cleaner than the rest has coolant seeping into them. If it's fixed early enough, chances of a new head gasket taking care of this issue is high. Keep driving it like that, you may buckle the soft aluminum machined surfaces so a head gasket replacement will only work for 50K-60K miles.

    YMMV
     
    #2 BiomedO1, Jan 4, 2025 at 8:28 PM
  3. Brian1954

    Brian1954 Senior Member

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    It's probably a bad head gasket. Very common problem on a Gen 3 Prius. Search for bad head gasket in this forum. You will find hundreds of threads to read.

    Here is a new thread that was just created yesterday. https://priuschat.com/index.php?posts/3504235
     
    #3 Brian1954, Jan 4, 2025 at 8:30 PM
  4. Mendel Leisk

    Mendel Leisk Witness Leader

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    Just bought it? If so, the stop-leak product is likely starting to let go.
     
    #4 Mendel Leisk, Jan 5, 2025 at 2:37 PM
    Brian1954 likes this.
  5. NutzAboutBolts

    NutzAboutBolts Senior Member

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    Have you checked the fuel injectors? Is the spark plugs soaked?
     
    #5 NutzAboutBolts, Jan 5, 2025 at 4:38 PM
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