Cylinder 4 Misfire/Random Misfire after Fuel Injector Replacement

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by oreomonster, Nov 20, 2022.

  1. oreomonster

    oreomonster New Member

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    2006 Prius
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    Long time lurker, decided to sign up do to an unresolved issue with fuel injectors.

    So here's the situation, A few months ago I started to receive a cylinder 1 misfire code so I replaced the following (sequentially as each replacement did not solve the issue):

    Vehicle: Toyota Prius 2006 (Gen 2)
    Mileage: 162k

    1. Spark Plugs (all four, Denso)
    2. Ignition Coils (all four, yes... expensive)
    3. Cleaned MAF sensor/cleaned throttle body
    4. Replaced PVC valve
    5. Put a bunch of different fuel injector cleaners but did not fix issue
    6. I then got a code for O2 Air/Fuel sensor, so I replaced both upsteam and downstream o2 sensors, code for O2 issue then went away.
    7. Replaced MAF sensor with OEM Denso
    8. Replaced all 4 fuel injector (refurbished)

    So the current issue is the following:

    1. After replacing all 4 fuel injectors, there was a loud leaking/vacuum air sound when the engine was turned on.
    2. Extremely loud knocking sound during idling. When I accelerate, issue goes away.
    3. Initially I received random misfire, then cylinder 3,4 misfire, finally cylinder 4 misfire (P0304)
    4. I also received an O2 sensor circuit code (P0136) and System Too Lean Bank 1 (P0304)

    Possible causes: When replacing the 4th injector, there was a bunch of fuel that poured into the hole from the fuel rail. Perhaps it has to all burn out? I drove around 10 miles, so I imagine it would have to solve the issue.

    The loud noise is only at low rpm's.

    Tomorrow I'll take a look to see if the air filter housing is leaking anywhere.

    Please let me know if you've had experience with this.
     
    #1 oreomonster, Nov 20, 2022
  2. SFO

    SFO Senior Member

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    Welcome to PriusChat!!

    Which OBD2 scanner are you using, and what OBD2 codes do you currently have?
    Were those purchased at the dealership, or via online?
    Did you disconnect the 12v battery to reset the learned fuel curves back to factory default?

    FYI : you're moderated until you've posted 5 times.
     
    #2 SFO, Nov 29, 2022
  3. mr_guy_mann

    mr_guy_mann Senior Member

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    Likely cause: during injector (fuel rail) installation, the lower O ring between #4 injector and the intake manifold was torn or out of position. This results in a large vacuum leak that's most apparent at idle. In turn you have misfire, codes (and noise from the transmission damper) because of that leak.

    2nd likely cause: the "refurbished" #4 injector has problems that cause that cylinder to not have enough fuel (restricted, sticking, electrical problem). Or a wiring - connector fault). Which could also account for most all symptoms and codes.

    Posted via the PriusChat mobile app.
     
    #3 mr_guy_mann, Nov 29, 2022
    Last edited: Nov 29, 2022
  4. prius530

    prius530 Junior Member

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    Have a gen 2 with 200k miles that was throwing codes P0304 and P0303 for misfire cylinders 3 and 4 and random misfire. Burned oil 1 qt per 1000 miles and switched to high mileage oil, which helped. Coolant levels were stable and oil was clean so I ruled out head gasket issues. Changed spark plugs, pcv valve, and coolant temp sensor which also had a code, but it didn't help misfire. Misfire codes disappeared and then reappeared intermittently. Finally narrowed problem down to fuel injectors that appeared overly wet with fuel. Maybe they were not spraying properly or leaking. Remanufactured OEM fuel injectors seems to fix problem. Hoping fuel economy which was stuck at 41 mpg will improve. Always used top tier fuel, and in the later months only bought Costco and shell gasoline with higher levels of detergents.
     
    #4 prius530, Mar 7, 2023
  5. oreomonster

    oreomonster New Member

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    You are correct. I fixed this by relubricating the O-rings properly (with a tiny bit of car oil) and now my car works fine.
     
    #5 oreomonster, Mar 15, 2023
    mr_guy_mann likes this.
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    #6 mr_guy_mann, Mar 16, 2023
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