TD68953 April 03 build got it in June, noticed it pretty soon. after Powerchip ECU from Randy its was not as bad but still present.

 

TD75106, sept build ,slight yo-yo. Tim

 

TD79087; Dec '04.

Someone needs to invent a Yo-Yo Smilie.

My car has pulley, powerchip ecu, alta intake, throttle body and plugs and the Yo-Yo before and the Yo-Yo after.

Milltek to come if Randy can ever get any in.

-early

 

TD51104 5/02 build

 

I have been away this past two days. Wow Ryan, THANK YOU for all the great work!

My car is TD74337, 04 MCS, 9/03 built. Yo-Yo in 2nd thru 6th gear.
Keep us posted!

After the yoyo is figured out, how about that "reverse stumble" around 1900rpm in deceleration. Does everyone/anyone have that!?

 

Ryan- Dec 2003 build in the house, yo-yo

I drove my car yesterday (just a pre-delivery check, was running errands right by the dealer) it's a Dec 2003 build. No stumble, started immediately in 7 degrees! However, it does have a slight "surging" around 3,500RPM, I assume this is the yo-yo? I wouldn't call it dangerous or destructive, but it is annoying.

I also notice when coasting into a light, right around 1,800RPM, I get a small fluctuation on the RPM's (up/down), seems to drop a bit lower than I'd like, but doesn't stall or anything.

 

TD72531 MCS 07/03 build. Has a yo yo through 2nd, 3rd & 4th on moderate gas. When given plenty of welly the yo yo is missing. Happens at just ove 3K rpm. Great work on this.

 

My Sept. 03 build 04 MCS has always had the yo-yo and it seemed to appear similarly to everyone elses.

Yesterday, during routine service, they upgraded my ECU to version 36. First impression is that after warmup the yo-yo is reduced to the point of being hardly noticable. The car drives much better with V36! I hope eveyrone else has the same result with V36.

 

Well, I dropped off Mr.Motor2 at MCM on Wednesday morning. I printed out the first 3 pages of this thread, along with about 21 of your VIN ID's of who said they also had the Yo-Yo. I had to shy away a few because they confused the Yo-Yo with the (now old news) Stumble, which are NOT the same problem. I have yet to hear any updates from either Mark Ferguson's MINIUSA contact, feedback from my dealership and their MINIUSA Engineering communications channel, or the VP of PR of MINIUSA that I met last week.

---> Katana; the "reverse stumble" upon in-gear deceleration, while annoying, I believe that is something that is inherent in manual transmission vehicles. I've always owned a manual tranny vehicle, and of the past 10+ manual tranny cars I've owned, every single one has exhibited this phenomenon. You'll notice that it only occurs at low speed and RPM, so I believe it's due to the engine lacking enough torque to engine brake anymore, subsequently unloading the gears and creating the percieved "reverse stumble". I hope that helps.

Until next time,
Ryan

 

I'm really sorry to hear about all you guys with the Yo-Yo problem. I have an April '03 build MCS that had the stumble but has never had the Yo-Yo. v3.6 completely fixed the stumble and now the car drives like it was meant to.

 

Just to add my name to the yo-yo chronicles.

TD70585 build date 6/03

 

Hello fellow yoyoers.

I have been following this thread for some time now. I actually suggested to BMW/Mini NJ that I thought the bypass valve was the cause of the yoyo several months ago. The bypass seemed like the obvious cause as it is surposed to be actuated right at 2,800 RPM which is right where the yoyo starts. In typical Mini style I was told that this had nothing to do with it. There was no explanation of any kind - they really don't want to know about it.

After having my service agent look at the car for the 6th time for the yoyo and post v36, they have now labelled the yoyo as a "characteristic" of the car. They did try to fix it 6 times though. Go figure? And yet many Minis don't have this characteristic.

I don't have my vin in front of me so I won't add it - not that I think it would do any good. BMW are very well aware of the problem and what is causing it. If not then they aren't the major manufacturer we all thought they were.

I have absolutely no faith in BMW Mini to do the right thing where these driveability issues are concerned. It took them more than a year to get rid of the stumble and who knows if they fixed the very dangerous bog issue - it is so intermittent and can not be reproduced at will. BMW have taken away any of the pleasures I had from this car.

It will be interesting to see what, if anything BMW come up with after being confronted with this thread.

For those of you who say that you only get yoyo in 2nd and 3rd gear, I'd venture to say that you get it in every gear but 1st. The bypass valve has no idea what gear you are in - all it knows about is the actuating vucuum. Apply the same torque load at the same RPM (2800 - 4000) and you get yoyo in any gear. The effect is more subtle in higher gears as it is geared out. At 70 MPH in 6th I can feel yoyo as I accelerate, but it is subtle - a bit like bad timing or a bad plug.

Go get em Ryan

_________________
'03 S DS

 

>>For those of you who say that you only get yoyo in 2nd and 3rd gear, I'd venture to say that you get it in every gear but 1st. The bypass valve has no idea what gear you are in - all it knows about is the actuating vucuum. Apply the same torque load at the same RPM (2800 - 4000) and you get yoyo in any gear. The effect is more subtle in higher gears as it is geared out. At 70 MPH in 6th I can feel yoyo as I accelerate, but it is subtle - a bit like bad timing or a bad plug.

I agree, and can make it happen in any gear, and not make it happen in any gear depending on the driving conditions of acceleration.

Unfortunately it might take a bad write up in a modeate to high profile car magazine, car tv-show, or consumer report for BMW/Mini to get off their *** regarding the issue.

For them to call Yo-Yo a characteristic is wrong. The toggle switches, and tac at the steering wheel are characteristics. The car shuttering along in acceleration is a design flaw/failure/oversight. My 2c.

 

I found out that the P.I.D. controller for the throttle body servo is in the ECU hardware. It can also be "tuned" via programing via the OBDII port, which means fixing the overshoot instability is only an upload away. This, combined with [my educated guess,] a stiffer closure spring in the bypass valve would hugely negate any Yo-Yo effect.

---> Tokio, thank you for your insight. From the type of feedback I've experienced thus far from MINIUSA, I'm not at all surprised to hear your story. Historically, MINIUSA is enthusiastic about paying off "lemon-MINI" customers rather than having to bother with actually engineering new solutions. I would absolutly hate to be forced down that path, especially since I've put so much money into aftermarket product.

 

And I thought SU carbs where bad
Great work Ryephile !!

 

Add mine to the long list of yo-yo'ers. '03 MCS, 11/02 build, #TD62476. Thanks for the hard work on this, Ryephile.
Pat

 

Kudos to you Ryephile! You've done a lot of hard work and we all appreciate it very much!

 

Please add me to the list of annoyed MCS-with-yoyo owners

TDS8656
Sept 03 build

 

TD 53564 June 02 S with Yo-Yo since Day 1

Does vacuum open or close the bypass valve?

Either way, the action of the valve could be damped by placing a restriction in the supply or exhaust port of the vacuum motor.

 

The vacuum line pulls a diaphram which pulls a tie rod that opens the bypass valve - to bypass the supercharger. When the throttle body opens, the vacuum is reduced and the bypass valve closes in proportion to how much the throttle body is open. A stiffer spring would try to keep the bypass valve closed, which in my experiments, is a good thing. Another experiment I haven't done is to drive with the throttle body tied open, or further still, completely untied (flapping around by turbulence in the induction system).

Update My Dealership replaced the bypass valve - only to find the Yo-Yo still there. This confirms that my old bypass valve was A) not bad, or B) the new one is bad too, or C) the design is bad. They have yet to hear back from MINI engineering, of course

 

>>Another experiment I haven't done is to drive with the throttle body tied open, or further still, completely untied (flapping around by turbulence in the induction system).
>>

Okay, I'm gonna assume you meant the bypass valve tied open, since tieing the throttle body open would make for a hell of a ride.

My assumption based on your experiments is that the the fluctuations in the throttle body caused by having too high of a Q is also causing the bypass valve to oscillate, give us the yo-yo. By tieing off the bypass valve, you removed a major power variation on the engine. I imagine the throttle body is still oscillating, but since the bypass valve is bypassed, you just can't feel it.

Now, since it is unlikely we can control the action the throttle body, but yet we also still want the bypass feature, my idea was to make it less responsive to inputs, namely the vacuum signal. By placing a restriction in the vacuum line, one could control the action of the bypass valve. In fact, if you used a one way vacuum valve, with a small bypass around it, you could make the bypass open quickly but close slowly depending on the orientation of the one way valve. It's hard to describe, am I making sense here?

I've noticed that when you are say cruising at 50 mph or so, and you quickly get of the gas then get back into the gas, the response is kind of abrupt. This may also be due to the bypass valve responding too quickly to inputs. A stiffer spring would help, but it should be easier for you to experiment with the vacuum source, unless the bypass valve assembly comes apart easily. If it does just put in some shims to make the spring stiffer, easier than finding a new spring.

 

I've tried / I am trying the experiment. I tied the bypass diaphragm linkage in the "no vacuum position" i.e. the same position it is in when the motor is off.

I think this means that all the incoming air will always flow through the supercharger and none of it will bypass the supercharger (to flow directly into the throttle body). Correct?

After a 40 mile drive to work, there is no Yo-Yo in all the traditional hills/gears and there is better throttle response (I think....). I even got the DSC to kick in around a corner from standing still and I was never able to that before without god-awful over revving and dumping the clutch.

Now the real questions are:

1) What will this do to the car? I remember reading this would make it run rich, have poor gas mileage, and possibly foul the plugs. Although I can't reason out why this would be? Shouldn't the computer just lean it out a little bit? (Maybe a dumb question...?)

2) Why would BMW put this whole rinky-dink mechanism in, if I can get better performance by disabling it? Is the answer to this “see #1 above” i.e. fuel mileage?

 

I was just digging around under the hood, taking a look at the valve. Leverage is limited, getting in there is tough.

What is the best way to pop off the linkage without breaking it?

 

My mini is stock (under the hood).

I just used a long thin tye-wrap(cable tie) to tie the valve/linkage to the molded plastic air intake "hose". It looks like crud. but it works so far.

One advantage is that it only takes about 15 seconds to snip the cable tie if it needs to go to the dealer....

If it turns out there is no disadvantage to this whole scheme I'll figure out how to pretty it up.

 

So you didnt bother to disconnect the linkage? It pulls on the valve that wont move?

I thought about doing just that, but didnt know what the consequences would be if that arm couldnt move freely.

Thanks