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offshores

2011 YZ450F Runs Like It Has Bad Gas Or... a Cold VW

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I noticed this a few rides ago. Bike fires up on 1st or 2nd kick no problem, idles great, but stumbles around for at least 2 or 3 mins when I start to ride. Doesn't matter if I'm 1/8th throttle or full throttle, it stumbles. I idle it for a few minutes and then check my oil before a ride so the bikes isn't cold when I take off. If any of you are familiar with taking off in a cold VW Bug/ Bus/ buggy and know that sluggish feeling, that's almost exactly what's happening. It misses, hicups, burps, whatever you wanna call it. I thought it was bad gas because I hadn't ridden the bike for a while and when it all of sudden starting running great after adding new gas I was almost convinced it was the gas. It happened again recently and did exactly the same thing. After about 3 mins it started running great and I rode for a good 90 mins w/o any issues. Again, thought it was the gas because I just don't ride as often anymore. Brought the bike home and changed oil/ filter, cleaned air filter, and pulled tank and emptied it. I got it all buttoned up and added new gas and took it around the block and same thing happens. It's not the gas. Just put in a new plug and no change. Anyone else ever experience this? If so, what was it or what should I start focusing on?

Thanks

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Anywho, checked the valves and they're in spec, removed throttle body assy and cleaned it, disconnected all the electrical connections and blew out with air and it still stumbles. I have another 2011 YZ450F and switched tanks to see if it could be a fuel pump issue and nothing changed. One thing that did make it run much better was disconnecting the the throttle position sensor. I unplugged it and it ran just fine, plugged it back in and it stumbled.

So, I'm back to ask if anyone has an idea of what I should try next?

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If disconnecting the throttle position sensor has an effect on it, I would start by getting the book and a meter and making sure it's in spec.

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Get the codes read.  In most cases, a TPS faulty enough to cause that will show up as a fault code.

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Thanks for the replies. I'd imagine when you say "the book" that means the manual???

Anyways, the bike that runs great gave me a reading of 4.87 ohms from the TPS and the bike with issues is reading 4.33 ohms. The manual says 4-6 ohms so good on both bikes.

 

I called a shop today and they said they couldn't even touch my bike until next Thursday so trying to tinker around with it myself in the meantime. Like I mentioned, I have the exact same bike sitting next to it so I might try swapping the throttle body assy next. Any other ideas before I do that?

 

Thanks again!!!!

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I'm not sure if there's something more than the GYTR Power Tuner (which I have) to read codes, but the only S/D Code that either bike throw is #15 when I had the TPS sensor unplugged. Fault code 15 means TPS signal is not received properly (unplugged). Plug em back in on both bikes and there are zero S/D codes.

 

Is the FI diagnostic gizmo something better for reading codes or will the GYTR Tuner I have be suffecient?

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The manual states 4-6vdc operating voltage and a max of 6.3k ohms.  I'm not an expert on Yamaha 's TPS, but it is a variable resistance sensor. It should read a certain resistance at 1/4 throttle, another at 1/2, 3/4, etc.  Unfortunately, the book (manual) doesn't give the range of measurements, at least not that I can find.  Instead they want you to have the special diagnostic tool.

 

Take your meter and measure the resistance of your 'bad' TPS at idle.  Loosen the screws and adjust it to match the resistance of your good bike at idle.  Then, leaving the meter connected to the TPS, watch the resistance readings as you slowly open the throttle.  It should slowly and smoothly increase.  If it jumps around, the TPS is bad.  If it steadily increases, that's good...then compare the resistance of your 'bad' TPS at full throttle to the resistance of your good TPS at full throttle. 

 

If you can get the readings of the 'bad' TPS to match (at lease close) to the good TPS and you're still having issues, then you can rule out the TPS as your problem.

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I don't know how bad your bike runs during the 3 min but if I hop on my bike cold it will hiccup a little for a minute or two before it warms up it doesn't bother me because it runs great other than that mine is a 2012 so same bike. I never really noticed it until after injectioneering modified my throttle body so that might have some thing to do with it. I'm not gonna take it to the shop and pay 100 dollars for them to look at it and then tell me there is nothing wrong you need to let it warm up. Lol

Edited by Mtrain730

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The manual states 4-6vdc operating voltage and a max of 6.3k ohms.  I'm not an expert on Yamaha 's TPS, but it is a variable resistance sensor. It should read a certain resistance at 1/4 throttle, another at 1/2, 3/4, etc.  Unfortunately, the book (manual) doesn't give the range of measurements, at least not that I can find.

Pages 7-7 and 7-8 are quite detailed, actually.  Pulling codes is a good idea anyway, and yes, the GYT-R tuner will do that.  The diagnostic tool will run much more exhaustive tests, but the tuner reads codes.

 

 

7-7.png

7-8.png

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The bike runs pretty bad for a little while and it's only recently done it so I doubt it's because it's cold. Plus it runs fine w/ the TPS unplugged...

Just curious what you mean by pulling codes? If my tuner doesn't show any codes then what exactly would I be looking for?

Edited by offshores

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Quick update. I swapped the throttle body assembly between the two bikes and the stumbling followed the TBA. Could this be that the TPS needs to be adjusted? It's just strange that the bike will perk back up to normal aftrer about 3 minutes, but runs great with the tps unplugged from the start.

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Then, no, it doesn't prove that the TPS is faulty.  It proves that either the TPS or the injector is faulty. 

 

Frankly, I'm a little surprised that the thing works at all without throttle position info.  It must have a backup algorithm to follow based on MAP info.  Either way, test the TPS according to the manual pages I posted.  When you get to step two of the variable resistance test, swing the throttle from idle to WOT and back slowly.  Watch for sudden changes in resistance that don't conform to a smooth progression up or down.  It seems likely it's a TPS problem, but you haven't really isolated it yet.

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Thanks for the info. I'm having a hard time thinking that it could be the injector. How would unplugging the TPS have an affect on a faulty injector and then all of a sudden make that fault injector work properly?

I was going to remove the 2 TPS from both bikes and switch them to see if the stumble followed the one in question. I read that adjusting these can be a real PITA so I didn't mess w/ either, hence swapping the whole assembly. Is that really the case? If I do in fact need a new TPS, will it be a PITA to install and dial in?

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Thanks for the info. I'm having a hard time thinking that it could be the injector. How would unplugging the TPS have an affect on a faulty injector and then all of a sudden make that fault injector work properly?

 

That's the reason that logic still points to the TPS, but the fact remains that switching the throttle bodies as an assembly doesn't categorically prove it. 

 

The process for the adjustment is there on the same manual pages I posted.  The book calls for the use of the technician's diagnostic tool, but I believe the GYT-R tuner can be used.  If it will display throttle angle, it can.

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It seems the issue has been resolved. I Rode the bike last Sat with the TPS unplugged and then Sun morning I plugged in the Tuner and noticed the T/P setting for throttle valve travel showed 5 at fully closed throttle and and 85 at fully open throttle. I never noticed that or knew it should be set at 0 and 80 respectively. I loosened the TPS and moved it clockwise a bit until it was set at 0 and 80. The factory marks on the TPS are no longer in line, but the bike ran great with it plugged back in. I wasn't too quick to update last weekend becasue there was some doubt that my bike may have run fine on the 2nd day (W/ TPS plugged in) of riding in a row when this problem first started. So, rode again yesterday after the bike sat all week and everything was fine. Bike fired up and never stumpled in the beginning with the TPS plugged in.

I'm now pretty confident to report that my problem was caused by a TPS that was out of adjustment. Why or how it was off is beyond me and maybe it's a sign that the TPS is going bad???

 

Thanks to those who offered up advice!!!

 

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