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p0304 after headgasket replacement

Discussion in 'Gen 3 Prius Technical Discussion' started by Amarprius, Mar 4, 2024.

  1. Amarprius

    Amarprius Junior Member

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    Vehicle:
    2007 Prius
    Model:
    Base
    I buy and sell prius, usually blown headgasket I dont usually mess with coils and plugs when I usually already know its headgasket, but the codes are usually cylinder 1 p0301, anyways got the headgasket replaced and got the car back and it is misfiring in cylinder 4 only. Also it does not misfire right at start up like usual but it starts misfiring about 1 min after its started. The mechanic usually cleans out the egr and the intake manifold but I am not there I dont know if it wasnt good enough. my question is would a clogged or not fully clean egr cause misfire, even though i dont think so but would you suggest swapping coils to see if it goes to another cylinder? spark plugs were change any other ideas?
     
    #1 Amarprius, Mar 4, 2024
  2. Brian1954

    Brian1954 Senior Member

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    III
    Yes, the first thing to try would be to swap the coils.
     
    #2 Brian1954, Mar 4, 2024
    Last edited: Mar 4, 2024
  3. Amarprius

    Amarprius Junior Member

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    2007 Prius
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    Base
    the coolant tank also has pressure build up but not a whole lot I just think the headgasket was not done right. But I guess I will try to swap coils
     
    #3 Amarprius, Mar 4, 2024
  4. TNToy

    TNToy Member

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    Location:
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    Vehicle:
    2012 Prius
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    Three
    The EGR would cause a misfire at idle if the valve were stuck open. It should be fully shut at idle or very close, not allowing any exhaust through.

    A simple test for this would be to loosen the pipe between intake and EGR valve and insert a putty knife to block the flow. Snug bolts down, start it, and see if problem disappears.

    If it does, the vehicle needs a new EGR valve. If it doesn’t, your problem lies elsewhere.
     
    #4 TNToy, Mar 12, 2024
    Brian1954 likes this.
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