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Stuttering engine at cruising speeds *** SOLVED ***

91K views 83 replies 31 participants last post by  Griffo37  
#1 ·
I love my bike, but this year it developed a problem that ruined my entire season.

Symptoms:
My 2014 FZ-09 has 30 000km on it and started stuttering while cruising around 30% throttle. It was getting worse as time went on. The stutter was becoming more frequent, under more riding conditions and was becoming violent. The bike was also starting on the 3rd or 4th pull instead of the normal 1st pull. It got so bad that is was happening in low speed situations. Once, it happened in the middle of a busy intersection during a left hand turn... only my angel and willpower kept me up. Disconnecting the battery or unplugging the ECU would improve the situation for a while, but after 50 km it was back.

The process:
I asked my Yamaha dealer to look into it during my maintenance service and they said it was bad gas (which ticked me off). Later they told me it was plugs, (which I had changed the day before myself). So I started cruising the forums to find a solution. I changed the air filter to a K&N and did the plugs. Then I did a reflash through VcycleNut. It didn't fix the problem. Then I replaced the injectors and tightened the throttle cable. While these all improved the bike, they didn't fix the underlying problem.

The Solution:
Finally, I decided to check all of my electrical connections. When I checked the connectors for the Accelerator and Throttle Position Sensors, I found condensation inside. I cleaned them out with electrical contact cleaner, let them dry and put it all back together. Low and behold, no stutter, jerking or hiccups. On top of that, 150km on, the bike is running smoother and starts 1st pull. My guess is that the APS and TPS must have been sending bad readings to both the throttle actuator and ecu. The actuator was opening and closing according to bad signals and the O2 sensor was reading rich as a result. The ecu was probably leaning the bike out based on the O2 data. Probably why it got better when I disconnected the battery. As the emissions data is rewritten in the ECU, the bike is returning to its normal fueling. Unfortunately it took the entire riding season to discover.

Recap:
Clean the electrical connectors for the APS and TPS to fix the problem. I plan on doing it every spring.

P.S. The VcycleNut flash greatly improved the bike. They have excellent customer service and maintain prompt correspondence throughout the process, it is also a cheaper alternative to throttle commanders and O2 deletes. Also, the manual states 1/4" play in the cable, that is WAY too much. Tighten to where its comfortable. (No wonder my right hand was always tired an numb.)
 
#7 ·
#11 and #13 in this pic.
Image


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#10 ·
Several years ago some overzealous rinsing put water into my APS.
The code showed up right after the wash job.
I was in denial for a couple of weeks until it totally quit out in the middle of nowhere!
After I replaced it I cut the old one apart and found this---------
 

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#14 ·
Way to stick with it!!!! Finding elusive problems like that is not for the faith of heart. Good job! Sorry it blew your season all to hell, but your sweat and frustration will benefit many fellow riders in the future.
 
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#22 ·
JM00JM,
You do NOT have to remove the airbox to access them. They are on either side of the intake tubes and the airbox does not obstruct you at all. All I do is lift the tank, rotate it and place it where my seat normally is (use a towel or something in between the tank and the bike to prevent scratches). With this method I don't even need to disconnect the fuel lines.
 
#28 ·
I found that too for a while. The connectors expand in the heat, breaking the airtight seal. When its cold the connectors contract again, trapping moisture. If this is the issue, it will get worse. I've taken to putting some dielectric grease on the seal of the connectors to prevent this. The connectors are on the left and right of the 3 intake tubes of the throttle body. It doesn't hurt to clean out the connector for the throttle actuator as well (on the rear side of the throttle body, a little to the right).
 
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#33 ·
Created my account and started my gold subscription just to reply to this post. 2016 FJ09 and I've done everything to try and resolve the stutter/surge. For me it happens around 2-3K RPM while giving very slight throttle inputs. So far i've done plugs and throttle sync, adjusted the aps sensor, new chain and sprokets, kev's o2 mod, Vcyclenut flash and block off plates, and recently removed the tank AND airbox to clean and grease all the electronic connections including the coils, injector connectors, APS and TPS, and even the battery terms. Right now I have the APS on order from amazon because of post #10 where @Shamrock describes water in his APS and I've ridden through LOT's of rain. @Shamrock, I would love to hear the symptoms that you had with the bad APS. I've tested the APS in diag mode while slowly turning the throttle very slowly and it seems to be fine hitting all the numbers but at this point I'm stumped.

My worst thought about the situation is that it could be a bad output shaft bearing as described here https://www.fz09.org/forum/6-fz-09-...um/6-fz-09-general-discussion/46434-gearbox-teardown-anyone-got-experience.html

With 21K on the bike I have been guilty of going long intervals without cleaning or adjusting and possibly over tightening and unlike the guy who got his output bearings replaced this bike has been down and repaired through insurance at the dealer and I'm pretty sure the Y.e.s. warranty is voided when this happens.

I'm hoping the APS sensor will solve the problem but it's on its way from Shenzhen and now amazon is saying it's "Delayed in Customs" so i'll be expecting that halfway through June if not July. I've been having this problem since last year and thought I just needed to replace the chain but after reading countless post about the surging/stutter experienced by tons of people on this forum I'm starting to get a little discouraged.
 
#77 ·
Created my account and started my gold subscription just to reply to this post. 2016 FJ09 and I've done everything to try and resolve the stutter/surge. For me it happens around 2-3K RPM while giving very slight throttle inputs. So far i've done plugs and throttle sync, adjusted the aps sensor, new chain and sprokets, kev's o2 mod, Vcyclenut flash and block off plates, and recently removed the tank AND airbox to clean and grease all the electronic connections including the coils, injector connectors, APS and TPS, and even the battery terms. Right now I have the APS on order from amazon because of post #10 where @Shamrock describes water in his APS and I've ridden through LOT's of rain. @Shamrock, I would love to hear the symptoms that you had with the bad APS. I've tested the APS in diag mode while slowly turning the throttle very slowly and it seems to be fine hitting all the numbers but at this point I'm stumped.

My worst thought about the situation is that it could be a bad output shaft bearing as described here Gearbox teardown, anyone got experience?

With 21K on the bike I have been guilty of going long intervals without cleaning or adjusting and possibly over tightening and unlike the guy who got his output bearings replaced this bike has been down and repaired through insurance at the dealer and I'm pretty sure the Y.e.s. warranty is voided when this happens.

I'm hoping the APS sensor will solve the problem but it's on its way from Shenzhen and now amazon is saying it's "Delayed in Customs" so i'll be expecting that halfway through June if not July. I've been having this problem since last year and thought I just needed to replace the chain but after reading countless post about the surging/stutter experienced by tons of people on this forum I'm starting to get a little discouraged.
ApS is air pressure sensor right. There's two of these shown on the parts diagram below