2015 yz450f major issue

Buddy of mine JUST told me today he's diagnosed a couple of hot-running problems with the EFI 450's and traced it back to that sensor on the TB.


Part number 15 on the TB exploded view.

Did you clean off that sensor and your air box yet?

Sensor #15 on the throttle body in the parts book is the manifold air pressure (MAP) sensor.  In and around the air box, there are two more, one is the Intake Air Temp (IAT) sensor (two leads; brown/white & black/blue), and the other is the Atmospheric Pressure Sensor (APS, or commonly, "BARO") (three leads; pink, black/blue, & blue).


Something to watch for, since the MAP sensor is connected to the intake port by way of a small hose, is for the hose to become degraded and get "sucked flat" by manifold vacuum and get stuck that way, cutting off the sensor from real time info. If the hose feels mushy, replace it. 

How would the sucked flat theory explain the consistent: runs good, cut off, and restart, runs bad idea

clean them already!! lol 

I cleaned out the air box and that temp sensor but no change.

Cleaning should occur regularly on any sensors that are downstream from an oiled air filter.


MAF sensor cleaner from an Auto Parts store does great.

How would the sucked flat theory explain the consistent: runs good, cut off, and restart, runs bad idea


It doesn't, necessarily, except that I saw this very thing on a Malibu once.  It didn't make a lot of sense, but the thing would very nearly only suck the hose flat on startup after it was hot.  I wouldn't put it at the top of a list, or anything, but stranger things have happened.

Yeah I'm at a loss on why the bike didn't throw any codes if something electronic Is wrong. And I don't really wanna start dropping $150 bucks here and there on sensors

Codes are set only when there is an electrical circuit fault that is detectable by the system, so the ability of the system to diagnose itself is limited by what's been designed into it.  It can see things like open circuits, short circuits, and resistance out of range, but can't determine whether the system is producing the right results.  So, if you have a situation, just for example, where a MAP sensor is electrically functional, but is blocked off from a vacuum source, a sophisticated system might call that out as an abnormal, out of range condition (impossibly low vacuum at speed, perhaps), whereas one intended only to identify electrical faults wouldn't notice it. 


What that means is that in addition to the electrical element of the sensor operation, you often have to examine the physical connection to the thing the sensor is supposed to read. That's where stuff like dirty probes and flattened hoses come into the picture.


Since the thing that's principally different about when it runs right and when it doesn't is heat, an interesting experiment might be to shut the bike down and then plug in a coolant temp sensor to the harness and just let it dangle there, see how it acts. Also check if the reading is in range on the original in your engine.

I have a 2010 yz450f. I was comparing part numbers. They used a different MAP sensor for '14-'15 but the '16 has the same as the '10. Any reason I can't plug the '10s into the 15. They look to have a similar plug

Could be any number of reasons for the different part number.  Try it.

I checked the hose while the bike was running bad. Isn't just the hose as well as squeezed the hose with some plyers and had no effect when it was running decent? That seems odd to me

It appears replacing the Map sensor and hose from my 2010 onto my 15 fixed the problem. Now what could have caused this?

Let me go way out on a limb and suggest that it was a faulty sensor.  


One thing you might do for fun if you have a vacuum pump/tester is see if the faulty sensor holds vacuum at all.  In their basic form, they are a potentiometer that shifts the output voltage based on the amount of vacuum they are exposed to, but if they become leaky, they won't register any change from zero at all, or very little.  Another possibility is that the device is physically stuck in one position.  

Had a bad crash not long ago (like bike did two full flips through the air bad) think that little guy is shock sensitive? Although it ran good for a whole day of practice. Hmm Idk but it's running good for now.

Now my same bike just had a coil go bad!

The crap luck seems to continue. At least you know what needs fixing this time.

Nope not the coil

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