2005 Prius P0301 misfire

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by BryceD15, Nov 6, 2013.

  1. BryceD15

    BryceD15 Junior Member

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    Hello all. I've read all the posts I can find regarding my problem. My prius with 125,000 miles is throwing a P0301 misfire code. It runs horribly rough at start up. Almost sounds like it's going to come apart. I replaced the spark plugs at 100,000, but I decided to replace them again when this problem came about. The cylinder 1 new spark plug is fouled looking after only 1 week of driving. I've cleaned the throttle body. I've cleaned the MAF. I've swapped igniters around to different cylinders, cleared the code, and it still came back cylinder 1. I replaced the pcv valve (I figured that needed to be done). I removed the spark plug and checked the spark on cylinder 1 to check the wiring harness and it sparked like a firecracker. I've basically done everything I can think of aside from tearing into the motor. What are the chances of a bad injector? Any help on this would be greatly appreciated.
     
  2. xpcman

    xpcman Senior Member

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    One guess would be oil fouling the plug. Is the plug just dark with carbon or a heavy deposit that might be burned oil? Any smoke in the exhaust that might indicate a oil leak into the cylinder?
     
  3. BryceD15

    BryceD15 Junior Member

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    I haven't noticed any smoke when following my wife in it. Only uses about 1 quart of oil every 5000 miles which I was told is within normal for a 125000 mile prius. It threw the P0301 code right away after replacing plugs also.
     
  4. Zedhomme

    Zedhomme Member

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    Definitely check the oil level like xpcman says. Besides fouling the plugs overfilling can foul the Mass Air Flow sensor and wreak havoc with engine performance. And the MAF and plugs would go bad again if not corrected. Also check your vacuum lines and fuel injector connections since you did plugs twice.
    Likely areas to check are:
    Open or short in engine wire harness
    Injector
    Mass air flow meter
    PCV hose connection
    PCV hose
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    A failed cyl 1 fuel injector which is spraying too much fuel is a reasonable possibility since you've swapped spark igniters and the misfire stays with cyl. 1.
     
  6. jadziasman

    jadziasman Prius owner emeritus

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    Have you checked the resistance of the coil pack on the #1 cylinder? If the resistance is too high, you won't get a reliable or sufficient spark to properly ignite the fuel and trigger misfires.
     
  7. BryceD15

    BryceD15 Junior Member

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    By coil pack are you referring to the igniter? If so, I've swapped igniters and the CEL misfire stayed with cylinder 1, so hopefully I've ruled that out.
     
  8. jadziasman

    jadziasman Prius owner emeritus

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    Well, you could have insufficient compression pressure in cyl. #1 or the connector from the wire harness to the coil pack or to the ECM could be faulty. Valve clearance is a potential cause.
     
  9. Bruce Cameron

    Bruce Cameron Junior Member

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    Just been down this path myself. I'd take an educated guess and say replace the injector or remove them for professional check and clean. I just bought a gen 2 cheap because nobody could diagnose it. It turned out to be a dirty injector, nothing more. Using a bore scope, (camera), it too looked very oily inside the cylinder, however simply unburned fuel due to misfiring. I used to work in a Toyota franchise as a qualified tech and the 2 archilles heels of these engines appear to be the injectors fouling and oil control rings if services are neglected. I suspect it is the stop start nature of operation that makes it more prevalent in these. As I am a mechanic, and have my own shop, I tore mine down and rebuilt it just because it costs me so little and I want to keep the car. But having said that I doubt it was absolutely required. I knew it had a bad service history so elected to make sure I knew what I had. In your case, simply deal with the injector as these engines are incredibly reliable mechanically. In the case of a misfire, it must be, in simple terms, fuel, spark or compression. Yes oil can complicte the picture but the amount ti takes to cause a persistant misfire, when plugs are fresh will always show as exhaust smoke. As Patrick hinted, swap parts to different positions and see if the misfire follows the components in oreder to diagnose. Best of luck!!
     
  10. Bruce Cameron

    Bruce Cameron Junior Member

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    My bet is you're correct. I've seen this exact scenario on the few occasions with these engines. Incredibly robust and have long service life however they do appear to foul injectors under certain circumstances, particularly cold weather and lots of stop start running. This is only anecdotal observational analysis, but beats the hell out of getting hoodwinked into an engine replacemnt that you don't need. Btw, I can tell you how to clean them yourself for cheap if you're confident and have the gear to do it.
     
  11. Joe 26

    Joe 26 Member

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    Next step should probably be a compression check.
     
  12. BryceD15

    BryceD15 Junior Member

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    I'm contemplating replacing the injector myself. How difficult of a task is this? I've seen something about depresserizing the fuel rail. Is this just as simple as disconnecting the battery, disconnecting the fuel rail and letting it squirt until depresseurized? I assume the head has to be removed to access the fuel rail, therefore is it a reusable rubber gasket or do I need new head gasket? Anything difficult or "special" I need to know about for tackling this repair? I really appreciate all of your input.
     
  13. Bruce Cameron

    Bruce Cameron Junior Member

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    A child could do it. You need a 10mm socket and a 12mm socket. Remove the air cleaner assembly. You will look straight at the 12mm bolts that hold the fuel rail in place. Simply remove these bolts, 2 of them. Wiggle the fuel rail away from the head, not too aggressive, and unplug the wiring to the offending injector, and wiggle the injector from the rail. At this point the pressure will release but it's not too scary. Place a rag over it to stop it getting in your eyes if you like. Simply put another injector from a wrecking yard perhaps back in place,making sure the O rings are in place, use a little wd40 if it helps to re-install it and replace everything in the same order. Fire it up and bingo, I bet it's as good as new again. Maybe cost 25 bucks, if you're lucky. I can post pics if you need help. It's really a 5 minute thing. The hardest part is going to get another injector. I don't kn ow if you have Echo's over there but all 1NZ toyota engines took that same injector, so doesn't have to be a prius. Good luck. As for the head gasket etc, no that is major surgery and as yet unrelated to this procedure. You'll be amazed how simple this is. BTW, don't give yourself hell by removing the air cleaner completely, just pop it up and swing it tone side, wires still in place, just so you can get to the injectors.

    Before you start, if there is dirt around the injectors, use compressed air to blow it all clean. If you don't, that dirt will go down into the intake as soon as you remove the injectors....not so god for the engine. Just a thought.
     
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  14. BryceD15

    BryceD15 Junior Member

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    That's great news to hear. I thought I had read something about removing the top of the motor to access the fuel rail and injectors. Sounds much easier than I had thought though.
     
  15. Bruce Cameron

    Bruce Cameron Junior Member

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    Nope seriously...dead easy. I can send pics if you get stuck. It's late night here now, so can do it tomoz if you like. In about 12 hours I could take step by step pics and post them. But if you can change oil, you can do this.
     
  16. BryceD15

    BryceD15 Junior Member

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    That'd be great if you don't mind. I'd really appreciate that. I won't be able to get to it until this weekend since I'm working the next few days.
     
  17. Bruce Cameron

    Bruce Cameron Junior Member

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    No probs Bryce, I'll see what I can do. I'm better on the spanners than the computer so maybe this will be interesting...lucky I have techno savvy kids. While I'm at it, I'll post details about how to enter it into inspection mode so you can run it to check it when done. It's just as simple.
     
  18. Patrick Wong

    Patrick Wong DIY Enthusiast

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    You might think that it is necessary to remove the engine valve cover when you look at the fuel rail. However it seems there is enough play between the fuel rail and the valve cover "finger" over the rail, so that you actually don't have to disturb the valve cover.
     
  19. Bruce Cameron

    Bruce Cameron Junior Member

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    Quite right. Yes it can be fiddly, but no, you don't have to remove anything else to do this, apart from the air-cleaner assy, even then you simply swing it aside out of the way, wiring still plugged in.
     
  20. BryceD15

    BryceD15 Junior Member

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    Update: last Thursday I ordered a new fuel injector. My Toyota stealership told me they "never" replace Toyota fuel injectors, but that I was welcome to special order one. I also talked to the service department and asked what the charge would be to replace 1 fuel injector. They quoted me $1050.... So, I picked up my special ordered fuel injector Friday afternoon. I had the new injector installed in 20 minutes. I started the car and the ICE started. It ran smoother than it ever has. Absolutely no roughness at cold start up now. No roughness at start and stop of the ICE. I can't remember when the last time the car ran this smooth. I've driven the car since last Friday with no CEL. So, $177 later it's fixed! Thank you everyone here for your help and giving me the confidence of tackling this easy fix.
     
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