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RLV199

2015 yz450f major issue

44 posts in this topic

So my '15 yz450f with less than 20 hours on it will start up but struggle to idle. It will run great as long as the idle is turned up and it runs hard for as long as you want it to but smokes a little, I suspect I sucked a little sand through the filter and &%$#@!ed my top end. The odd part is it WILL run and pretty decent until I cut it off even for a brief second then I star it and it runs like complete crap. Sounds like it is missing and popping. Here is a video link. It take a little while for it to act up (other than sounding like I need rings.)

https://youtu.be/sjW801aWHLY

I'm no expert mechanic but I am experienced enough to know there is more to the story than the top end. Took it to my dealer and they say nothing is reading wrong on the computer. They say the top end is causing it to run like that. But I don't understand why it would go from running hard and decent to complete crap after I shut it off and then start again.

Please help because my local dealer could not. I've had a few opinions and they all say it is something electronic but no one can say for sure what it is.

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Check compression first.  Oil only gets to the combustion area one of two ways - rings, or valve guide seals.

 

As for the electrical, no clue.

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Three, counting the head gasket.

 

From the video, I'd be looking for a fuel delivery problem first. 

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Yeah I would think fuel pump or injector possibly. A friend of mine had a very random stumble or miss on his 14 and it ended up being his fuel injector if that counts for anything.

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Posible injector issue? I don't think it would be the head due to that being a mechanical issue and constant then what you are having being a sporadic issue.

 

I would look at the fuel delivery first. If it was electronic I would think it would send a code, not sure how many codes are on the WR.

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Yeah the bike didn't throw any codes. Says my dealer, who denied there being any problem other than the obvious top end

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The October Motocross Action has a product on page 66 made by motocross plus that locks down the spark plug cap on current YZ's. It says that when the cap is loose the bike will run but the power will be intermittent or bogged down. The web site is www.motocrossplus.com

I couldn't locate the part but you can contact them. I believe it's run by Matt Bisceglia's father.

At any rate make sure the plug cap is on tight.

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Compare your bike for that sound to another one that is at near idle. I don't like the top end noise that it's making. Was it run out of oil or if it sucked major sand something could be toast.

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It was never run out of oil at all. Or antifreeze. Or anything but it did all begin at the same sand race

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Clean your air flow sensor in the bottom of the air box. It might be covered in filter oil. My friend had an issue that sounds like that, and thats what it was

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Looking at the exploded view now.  There's a temp sensor in there - is that what you're referring to?

 

An air flow sensor directly underneath an oiled filter would be a horrible idea.

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Per manual specs. We have narrowed the problem down to pretty much a bad ecu. Friend with the same bike is going to let me plug his in to the bike to see if it works.

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Per manual specs. We have narrowed the problem down to pretty much a bad ecu. Friend with the same bike is going to let me plug his in to the bike to see if it works.

 

If you have a bad ecu, it went bad for a reason, like a shorting wire against the frame....

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Is that typically the case? I went through the wiring harness rather thoroughly and most of the components with an ohm meter. Everything the Manual says points us to believe it is the ecu but I can't imagine why. The bike has less than 20 hours on it and it's 2 months old.

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Looking at the exploded view now.  There's a temp sensor in there - is that what you're referring to?

 

An air flow sensor directly underneath an oiled filter would be a horrible idea.

Yes thats the one. Clean it and disconnect it that should fix the problem. If not i have no idea. My friends bike was doing the same thing he thought maybe it was his wire harness and took everything apart which didnt fix anything. Then he brought it in to our shop to have the tech look at it. This is what he did and she was running great in no time.

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Looking again at the schematics, there's also a pressure sensor in the side of the throttle body, as well as a throttle position sensor.  So 3 inputs to the FI system in that intake system to qualify.

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Could a stator going bad cause this type of problem?

What kills me is how consistent it is. Cold the bike starts and runs decent, has plenty of top end power. You can ride it for as long as you want with no change or problems. But the second you cut the bike off while it is warm and start it again it won't Rev over 5k without cutting out and popping and spitting.

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