Ups and downs (sawing or jerking) on slightly open throttle
 

(Excuse my English, it�s not my native language. I�m Greek, living in Crete.)

History:
XT 660 R, 2004 model, problematic TPS was changed by Yamaha for free, good condition, 30,000 kms (19,000 miles), prior owner is a gentle and careful rider. I bought it 10 days ago. I visited Yamaha authorized service, where they detected a very slow idle speed (around 1,000RPM) which they raised to normal.

The issue:
If we divide throttle opening in a scale from 0% to 100%, the bike runs fine from 20% and above. Real power, excellent acceleration.
The problem appears under this 20%, when i.e. I want to keep a steady speed of 70 or 80 kms/h, (47mph) which is my usual way of driving. Engine goes up and down, as if the injector doesn�t know how much to spray. The feeling is that engine does on-off continually.
Things get worse when I close the throttle a little bit more (not entirely), let�s say to the 5% of this theoretical scale. The ups and downs become severe. The bike trembles. Turning the throttle off (0%), this �sawing� stops, but the bike decelerates more than I wished it to.

Some solutions I�ve read around the web:
Use better fuel (100 octane�s)
Enrich the gas-air mixture
Change air filter (mine is brand-new)
Decrease the input of air temperature sensor on purpose, so ECU senses �cold�

I don�t agree with any of the above and I can�t accept that this bike was constructed to behave like that. Any ideas -or links to similar previous posts- would be very helpful to me.

Although it wasn't designed to be like that, sadly a lot of them are!

Have a read through the threads in the links below. They will give you some ideas as to mods that can be done to smooth out your XT...

(1) Join XT660.com supporters to access the “Ask Kev” 1:1 technical help section - http://www.xt660.com/payments.php

(2) Check you haven’t got a dodgy TPS (which you’ve already done and got fixed) - http://www.xt660.com/showthread.php?t=948 Yamaha Recall

(3) Check you haven’t got a dodgy ECU - http://www.xt660.com/showthread.php?t=519 Yamaha Recall http://www.xt660.com/showthread.php?t=8546 (How to recognise the different ECUs)

(4) Twist-grip mod - http://www.xt660.com/showthread.php?p=154983

(5) Cush drive rubber mod - http://www.xt660.com/showthread.php?t=12422

(6) Adjust your CO - http://www.xt660.com/showthread.php?t=55

(7) Adjust your TPS - http://www.xt660.com/showthread.php?t=56

(8) Fit Kev’s fuel mod - http://www.xt660.com/showthread.php?t=194

Click on the link in my signature for the full list of all the mods available – and it’s a long one! :015:

Thanks a lot, I will read all of the above links

Another one to check is the chain tension, on the xt range a slightly too slack or loose chain can make it feel like what you describe.

Thank you for the advise to check the chain tension, my engineer did that today, but ups and downs go on... I'm thinking of changing the ECU 5VK-8591-A00 with ECU 5VK-8591-A01 from 2005-2006 models. Has anybody tried that?
Thanks again

The 01 ECU was used as a replacement by Yamaha to cure surging on early 00 ECU equipped bikes, so it's been tried and tested.

Changing to an 01 ECU will make a big improvement in reducing surging, in fact it can almost be completely cured on an 01 ECU with a fuel mod or Power Commander.

Another question, which I�m sure has been answered before, sorry for asking again.

If I buy a brand-new ECU (the A-01) and install it at authorized Yamaha service, I don�t need to change locks and keys

But if this ECU (the A-01) has been previously used on a bike, then I have to change the central lock too, because of immobilizer

If your bike has an 00 ECU fitted and has not already had the ECU changed to an 01 or a "white spot" 00 ECU, then I suggest the first thing you do is go and have a chat with your dealer. See if you can get it swapped by Yamaha at their expense as the early bikes with 00 ECUs were subject to a recall.

Have a read again of these two threads from those mentioned earlier:

http://www.xt660.com/showthread.php?t=519

(ECU recall information)

http://www.xt660.com/showthread.php?t=8546

(How to recognise the different ECUs)

Dear Pleiades,

Thank you for all that info, I have read them carefully. Particularly those two (519-ECU recall information) and (8546-how to recognize the different ECUs) made me believe that it�s probably an ECU issue.

The engineer of local authorized service talked with the chief engineer (of Yamaha Greece) few days ago and he informed me that they do not intend to replace my ECU. Fortunately he managed (yesterday) to tune the bike and he succeeded to reduce this surging. The bike is not surge free, but it�s improved. At least it�s safe.

I keep on searching for a brand-new ECU, the 5VK-8591-A01 and I will be grateful to anyone who can tell me where to buy one on a decent price.


Pleiades, thank you for all your help

Michalis

Get a price on this part number 90891-30032 same ECU as 01 & half the price.

Kev, you have posted

" Get a price on this part number 90891-30032 same ECU as 01 & half the price."

Where can I get it from?

Michalis

Give that part number to a Yamaha dealer, the part number is a warranty replacement ECU at half the price of a retail one, the dealer can order one in for you.

Thak you very much, Kev. I hope Yamaha in Greece agrees. I will ask them at once.

Dear Kev,

Yamaha in Greece (Motodynamics it�s called) answered to my local dealer, �this part number 90891-30032 was a replacement code and it does not exist any more. We do not have it� (my translation)

That�s what my dealer told me on October 9th, 2014, when I asked him to order this spare part for me. Earlier, on October 2nd, 6th and 8th, I had sent 4 e-mails to Motodynamics� site, but nobody answered to me. Nice policy so far.

Searching for spare parts in their site ( http://www.yamaha-motor.eu/gr/servic...gue/index.aspx) , I entered my bike�s frame serial number VG5DM011000007149 and I discovered that 5VK-8591A-01 is the one and only spare part for my ECU. (which is 5VK-8591A-00)

So, I had two solutions. Either to try to get this ECU abroad, or find it �as a used part- in Greece. I did the 2nd and soon it will be on the bike. I also bought the central switch, the fuel tank cap, the seat lock and all the three keys, red and 2 black. I paid 300 Euros, so I hope it works. I will keep you posted.

Of course I�m disappointed from Motodynamics� response (non response) to my e-mails, mainly because I wrote to them in a very polite way without asking anything for free. I just needed to be informed by them, since their experience in XTs� troubleshooting must be great. Pity.

If I ever think of another bike in the future, new or used, it wouldn�t be a Yamaha. And before I buy anything, next time, I will have a good look to the forums.

Thank you Kev, Pleiades and all other guys for your help

Michalis

I have just changed the A-00 ECU with a A-01 and (so far) I see a great improvement in bike's behavior. No cutings out, smoother acceleration and decelaration. Thank you all for the information and help.
Michalis

Good news mate.

I paid for my 01 ECU on my 2004 XTX to sort the problem even though the bike was under warranty, I then bought another 01 ECU & complete wiring loom & fitted it to my 2007 XTX so I could remove the O2 sensor as I had problems tunning my bike bore kit & high lift cam.

2 years later I worked out how to over ride the O2 sensor completely & turn off the O2 closed loop circuit, one year later I started building O2 controller as a plug & play mod & so the story goes on.