Fluctuating RPM then stall, every time...

[realman]

Gentlemen,

2016, completely stock, 13k miles and no hickups.

Rode 20 miles, no problem. Shut down for dinner. Ride 5 miles. Check engine light comes on halfway through. But no code is shown on the display, so I figure it isnt an emergency. Shut down for an hour. Start it up, no engine light now, no throttle input, in neutral. It runs smooth for five seconds, then starts reving up and down between 1k and 2k rpm for a few seconds, then dies. If I give it throttle it will do the same thing, just at whatever rpm range I hold it at, but it still dies on its own after a bit. Same thing over and over, no matter what I try.

TPS seems fine, ranges smoothly from 0.7V to 4.0v

Coils seem fine, measuring in at 1.7 ohms initially and sinking to 1.3 ohms(exactly as a new coil does that I tested).

I changed the plugs, the old ones seemed fine. No unusual deposits.

Battery is 1 year old, and is 100% good.

Fuel should be good as far as I can determine.

No air leaks that I can see.

Disconecting the o2 sensor does not change behavior.

Disconecting the battery and reconecting did not change behavior.

Code reader says the link cannot be established to the bike.(but it is a cheap harbor freight reader)

Very odd considering it can run smooth for a few seconds. Leads me to think that nothing is clogged, must be some sensor or computer issue. I would greatly appreciate any input. Thank you!

Edited April 27, 2023 by realman

[ElGonzales]

My bets are on "MAP sensor defective".
I have a small database where I collected problems and the solutions, your description fits very well.

You find the sensor on the left side oft the fuel tank, the vaccum hose of the left throttle body is connected to the sensor. It is possible to check it. This is how the output voltage reacts to a change of the connected negative air pressure. I tested a cheap Ebay GM Type Megarock Motec Vauxhall  MAPSensor because it looks exactly like the original Yamaha sensor   :

 

[realman]

Thank you will test it now

Edited April 27, 2023 by realman

[realman]

$130 sensor, yikes. The hose is clear. The sensor reads a constanr voltage when sitting. It is rather difficult for me to give it precise pressures to test whether there is an issue at some specific pressure. Voltage does decrease gradually while applying suction and it increases when applying pressure

Edited April 27, 2023 by realman

[ElGonzales]

You have to suck  
The output voltage should drop the more you suck the air out of the sensor and behave linear.

Yamaha calls the sensor Intake Air Pressure Sensor.

Similar Problem:
https://fz07.org/thread/14051/2015-fz07-help-please/?tab=comments#comment-185141

I think you have to measure voltage with the postive  probe at the pink/white cable, the negative probe to black/blue.
The service manuals mentions a normal voltage of 4.2 V at 119.99 kPa.
Blue shoud be the constand supply voltage.

Because of the high price I startet to search for alternativ aftermarket sensors, I bought one that seems to be identical but never compared it directly to the yamaha sensor. It's stored in my shelf but I am to lazy.




 

Edited April 27, 2023 by ElGonzales

[realman]

I never thought I would love a motorcycle so much. Ambient is 102kpa and it reads 3.4V. When sucking it goes down to 2.9V. Maybe I can call a girl over if we need a lower reading.

 

Indeed, blue is 5v and black is 0 with respect to ground. The white pink is as you said.

[realman]

In hindsight the simple solution here is to unplug it and see if it runs. Indeed it does run fine(but not 100% smooth) without it. I will buy a new one. Thank you again, friend. Your wisdom saved a lot of time!

[ElGonzales]

If this works that was a good idea I have to remember.  I hope there's no other problem like a damaged ECU or cable insulation that needs vibrations of the running engine to show up.

Without the diagnostic computer tools of a professionel workshop we need a little bit of luck and practical thinking

Another sensor that could be problematic for fuel injection is the intake air temparature sensor, but I think this will give you an error code in the dash. It is located on the right front of the fuel tank.
 

[realman]

I will let you know if it works. They were $28 new on ebay. Should arrive next week.

I did measure the temperature sensor. It was constant at 2.0V

[realman]

On 4/27/2023 at 3:24 PM, ElGonzales said:

If this works that was a good idea I have to remember.  I hope there's no other problem like a damaged ECU or cable insulation that needs vibrations of the running engine to show up.

Without the diagnostic computer tools of a professionel workshop we need a little bit of luck and practical thinking

 

So the new sensor I got from ebay is just some chinese fake. The bike will not start with it installed. It will fire the cylinders for maybe half a second then immediatelg die. Still runs fine if I have nothing plugged in at all.(slightly rough idle).

 

Is there some procedure for calibrating a new sensor that I am unaware of? Didn't see anything from searching around.

[Pursuvant]

54 minutes ago, realman said:

Is there some procedure for calibrating a new sensor

There is at least one, the "idle air control motor" (that is called the "Stepping Motor" on  Yamaha parts list), is has a procedure in the OEM Service Manual when it's replaced. 

You have fluctuating across your idle & throttle open positions, this part is described for some fail to idle smoothly/or idle at all  (fyi it has a spring & an o-ring parts that go with it, if it is a problem). It's in between the throttle bodies. But I think you and 

@ElGonzales

are already on the right path to this problem.