P0301 mystery occurrence

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by goodMXguy, Feb 12, 2019.

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  1. goodMXguy

    goodMXguy Junior Member

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    amazing community!
    I am getting code p0301.

    1. Does anyone have any idea why my a Prius will give a misfire only when the car starts?

    2. I think rain or snow is present when I get the code, but I am not 100% sure there is a relation.

    What I have done:
    - I changed the spark plug again recently, but the code came back.
    - I swapped the coils cylinders with 1 & 3 to see if the problem was there, but the code p0301 came again.
    - Checked that there are no loose cables or covers (not sure if I know all I need to check but did my best).

    Background:
    Previous fixed issues (and tread) were code C1241 + P0300 + p0301 + p0302.
    15k miles ago I changed the spark plugs, the PCV valve, 4 Spark plugs, cleaned the MAF sensor and throttle body, and have applied chevron fuel injector cleaner periodically since.

    My thinking and where I am:
    I read that the possible culprits could be the fuel injector, a vacuum leak, and the cables that connect to the coil cylinders.

    - A vacuum leak: I wanted to check the vacuum leak, but I am not sure how to go about it since I don't fully understand the "anatomy" of the system. I am attaching a photo of the vacuum system diagram that was on the back of the hood with the hope that I can get some help understanding the diagram. I am planning to use propane gas or a homemade smog leak tester.
    - I am considering changing the coils cylinders. Do I need to change all of them ($$$) with OEM part. My question is if it's worth it or if it is enough to change the one that corresponds to cylinder 1?

    I did fix my car once with the help of this forum, so I help I can continue with that!!!
     

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    #1 goodMXguy, Feb 12, 2019
  2. fotomoto

    fotomoto Senior Member

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    I'd suspect the fuel injector on that cylinder then, possibly, the wiring. A set of four is a whopping $28 on ebay.
     
    #2 fotomoto, Feb 12, 2019
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  3. goodMXguy

    goodMXguy Junior Member

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    #fotomoto. Thanks for replying! How do you check the fuel injector? Where is located?
     
    #3 goodMXguy, Feb 12, 2019
  4. fotomoto

    fotomoto Senior Member

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    You can't really check the injector without specialized equipment. You could move the suspected injector like you did with the coils to see if the code moves with it. BUT TBH if you have to ask where they are, you should have a mechanic handle this.
     
    #4 fotomoto, Feb 12, 2019
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  5. Landon51

    Landon51 Member

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    I think the easiest way would be to buy an automotive stethescope. You can hear the injectors when they are and are not working correctly. ($5 at harbor freight right now).

    You will have to Google what to listen for. I can't remember.

    Posted via the PriusChat mobile app.
     
    #5 Landon51, Feb 12, 2019
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  6. goodMXguy

    goodMXguy Junior Member

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    Thanks #fotomoto. That gives me a lead!

    I don't know where the injections are, but I will do some research and if I don't feel safe, I will take it to my mechanic.

     
    #6 goodMXguy, Feb 12, 2019
  7. goodMXguy

    goodMXguy Junior Member

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    I didn't know that, thanks for replying. I will check it out.
    Do you happen to know why I get the code when starting the car? It seems to be OK if I let the car warm up...
     
    #7 goodMXguy, Feb 12, 2019
  8. padroo

    padroo Senior Member

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    There is a tester for fuel injection but it is not for the novice.


     
    #8 padroo, Feb 12, 2019
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  9. Landon51

    Landon51 Member

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    These are what I was talking about: 1550115570479.jpeg 1550115644980.jpeg
     
    #9 Landon51, Feb 13, 2019
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  10. padroo

    padroo Senior Member

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    Do you get any other codes? You say it runs OK once it is warmed up, kind of makes me think it is not the fuel injection. It sounds like it is running bad in open loop and runs good in closed loop. This would have to be confirmed with scan data.
    I would do the easy stuff first, clean the throttle body, MAF sensor, look for vacuum leaks and make sure your coolant is filled to the proper level. All of these are cheap easy checks.
     
    #10 padroo, Feb 13, 2019
    Last edited: Feb 13, 2019
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  11. goodMXguy

    goodMXguy Junior Member

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    #padroo.
    I am puzzled because now is just fine... I think what you are saying makes sense. I have torque app + obd reader and I can perhaps use it for this. It has a component status, air temperature, coolant temperature... I would have to look more. How do you measure the scan data? What are the normal levels?

     
    #11 goodMXguy, Feb 16, 2019
  12. goodMXguy

    goodMXguy Junior Member

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    there. So, you were asking if I got other codes. I am not getting P0300, P0301, P0302. This is after I changed the 4 coils cylinders... I can also go ahead and change the fuel injectors, not that much to buy refurbished ones on Ebay, but I would hate to replace them and find out that this is not the problem either...

    I noticed that every time I have gotten a code is in the first minute of starting the car. Not sure if this indicates anything...

     
    #12 goodMXguy, Mar 4, 2019
  13. Skibob

    Skibob Senior Member

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    Doesn’t the fuel system spray more gas into the engine when you first start it up? Kind of like what a choke used to do? Perhaps that injector has some kind of problem and that extra fuel brings it out. With the amount of work you have already done spending 28 dollars isn’t that much. Plus if it doesn’t work at least you know it’s not that. You don’t say how many miles the car has but it might not be a bad idea to change them if the mileage is high.
     
    #13 Skibob, Mar 4, 2019
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  14. goodMXguy

    goodMXguy Junior Member

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    Hi @Skibob. I have about 126K miles. Do you think that is about time to change? Not that high as some people in this forum, but also more than 100K.

    I am considering cleaning the throttle body and MAF sensor as @padroo suggested. Also, it may be just easy to change the fuel injectors in the same day if I manage to do so.

    I forgot to mention that I also checked that the coolant and oil levels were OK. Oil level was a bit low, but it's still early for a new oil change, so I just added a bit more.

     
    #14 goodMXguy, Mar 4, 2019
  15. Skibob

    Skibob Senior Member

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    That would be low mileage to have a clog but anything is possible.
     
    #15 Skibob, Mar 4, 2019
  16. padroo

    padroo Senior Member

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    When a car starts it runs in what is called " Open Loop ", this is a default computer strategy on start up, O2 sensors aren't used yet. When it warms up it goes into " Closed Loop " and stays there unless the car cools off.
    If you had Techstream, Toyotas scan tool on a laptop you would have access to the same information the Toyota techs have in troubleshooting your car.
     
    #16 padroo, Mar 4, 2019
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  17. goodMXguy

    goodMXguy Junior Member

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    @padroo.

    I will check Techstream. I have it, but it doesn't work that well so I haven't try again. Long story, but I will report back. I have some screenshots from Torque... My AC wasn't working that well in the summer. Is the coolant temperature OK? It is close to 180 degrees...

    My next step is to replace the fuel injectors, clean the throttle body, and the massive air flow sensor... I am waiting to have time and a nice day at the same time.
     

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    #17 goodMXguy, Mar 9, 2019
  18. goodMXguy

    goodMXguy Junior Member

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    Help! I did change the fuel injectors, but now they are leaking! I spend 4 trials at doing this without success... It's a PITA since you have to remove a lot of stuff and reassemble it and then find out if you installed correctly or not...

    Does anyone have a video of how to disassemble the fuel injection rail? I only loosened the gas line and the two bolts that are in the front, but the fuel rail attachment is hard to remove. Also, I may have messed up the small O-rings ;( because I didn't use lube...

    I followed these instructions... Very helpful, but I still messed up :(
    2008 Prius fuel injector replacement DIY | PriusChat

    I guess at this point I need to find the O-rings or buy a new set, or just give up and go to the mechanic...
     
    #18 goodMXguy, Mar 13, 2019
  19. Tcortez

    Tcortez Junior Member

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    Do you ever find the problem?
     
    #19 Tcortez, Mar 24, 2019
  20. goodMXguy

    goodMXguy Junior Member

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    @Tcortez at all. I changed the spark plugs, coil packs also as I had mentioned.

    Some updates: I finally was able to change the fuel injectors with new o-rings (I messed up bcs I was not careful the 4 times I tried). The fifth was the charm. I still see a few misfires, I am not sure if misfires are a natural occurrence at a lower rate, I hope someone can clarify that. I haven't gotten a P030X code since though. I need to test once more with my OBDII sensor to be able to report on that.

    As I was disconnecting the air assembly, I noticed the big tube connector has a crack by the end where it connects to the air assembly. I taped to prevent further damage and also to prevent a vacuum leak in that part. I still think I may have some air leak or some lower fuel compression or something... Not sure... What I can tell is that my MPG went up. I was getting 34 mpg to 38 mpg and now I am getting 41>.

    TBC
     
    #20 goodMXguy, Mar 26, 2019
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