>>The who Yo-Yo thing confuses me. If it's something that Ryphile actually fixed by physically doing something in the engine, shouldn't EVERY car have the Yo-Yo?
>>
>>It's not like one MCS is gonna have a different spring stiffness in the bypass valve than another MCS
>>
>>

I should let Ryan respond but I'll take a stab at this one...

The two "Ryephixes" effectively mask the root problem's cause: software-generated overshoot (lack of dampening) based on the throttle body's pid sensor. The problem is not mechanical. However, both the zip tying of the actuator (Ryephix #1) for the supercharger bypass valve and the stiffer bypass valve diaphram spring (Ryephix #2) mechanically dampen the oscillations induced by the faulty ECU code's overshoot.

As to why some 04 MCS owners report the yo-yo and some do not, I think that at least three things must be considered. From my post on MINI2:

Perceptual Sensitivity - That is, how sensitive a person is to a very mild case of the yo-yo effect. Some people are very sensitive to a car's "behavior". Usually, these are the folks who have been introduced to vehicle performance and dynamics through competitive experience or just plain fanaticism. I have had friends drive my MCS through the yo-yo rpm band while I was riding in the passenger's seat. They did not feel what was so plainly evident to me!

Driving Style - Awareness of the yo-yo could also be influenced by a person's style of driving. I confess to being a "brisk accelerator" and normally find myself in the yo-yo's rpm band quite frequently. On the other hand, my wife and oldest son shift well before the rpm band and, consequently, think I am bonkers about "this yo-yo thing".

Manufacturing Tolerances - (This is rather speculative!) There are at least two mechanical/electric components that can amplify/attenuate the yo-yo: (1) the throttle sensor and (2) the bypass diaphram spring.

If the sensor is a little dodgy, the ECU software might not respond with the same level of "overshoot", thus limiting the signal that causes oscillation of the supercharger bypass valve. Conversely, the misbehaving sensor might also cause the ECU code to amplify the oscillation.

Ryephix #2 masked the effect of the yo-yo by the use of a stiffer (homebuilt) bypass valve diaphram spring to dampen the ECU-generated oscillation. Were the engine manufacturer (Tritec in Brazil) to use a batch of bypass valve diaphram springs of slightly different (stiffer) spring rates, the effect would be a similar masking of the yo-yo.


All this raises several interesting points in my mind:

(1) There is a "human factor" to the reporting of the yo-yo presence;
(2) Driving style may influence the perception of the yo-yo;
(3) There may, in fact, be some mechanical factors that can afftect the yo-yo's severity;

And, finally...

(4) At some point in the history of MCS production, the ECU code that reads and responds to the throttle sensor was modified without proper regression testing.

Earlier ('02s and a fair number of '03s) MCSs did not have the yo-yo at all. When their owners updated to higher ECU software versions (v.34? or above, I believe), the yo-yo was introduced. So, someone at Siemens was fiddling with the software (reason unknown) and the company did not apply standard white-box and regression testing methods before releasing it to MINI for production. Herein is my engineering concern.

With so many of our cars' functions being controlled by computer software, and the inherent potential danger that a piece of poor code could introduce into the cars' operation, why isn't the most stringent level of software testing being demanded by automobile manufacturers?

Just my two pence,

Theo


_________________

 

I just read Koopah’s post and now I’m really confused about this whole subject. I thought that the Yo-Yo typically occurs in the lower RPM range around 2,000 rpm and in 2nd gear. Everything Koopah says makes a lot of sense to me until he says that he gets it because he is a “brisk accelerator” which makes it sound (to me anyway) that the Yo-Yo occurs in the higher RPM range since I think that shifting at 3,000-3,500 rpm is rather conservative.

Can somebody point me to the “official” (by NAM standards) description on the Yo-Yo!

I only have about 3k on my ‘04 MCS and have only observed one minor problem with the engine management system - - when decelerating (foot completely off of the throttle) there is often a very slight “bog” as the engine speed passes through about 2,000-2,500 rpm. I’d describe it a a characteristic of the car except that the BMW/MINI haters would characterize that as something that the “criminal” BMWUSA executives have directed their “unscrupulous and lying” dealers to tell us poor unsuspecting MINI owners.

 

when does the new Puegot engine come aboard...this problem appears unfixable by BMW....32K miles on 02 MCS....always been there from day one and never any better with all the software upgrades....been told by BMW service techs to just get used to it, a characteristic of the engine....nice design work on the supercharger integration as the regular MC's I have driven don't have it.....was the supercharger just an after thought by BMW to get more performance after the Pentagon engine was already designed for the MC and Mini One....and they just can't get it right??
I test drove the MCS Works at the dealer and unbelievably it had the stumble as well, I looked at the rep riding with me and he just laughed and said, they are working on it and a fix should be here by XMAS...that was last October....lol !

 

Very well put Koopah. The Yo-Yo is an oscillation of the bypass valve due to under-damped throttle body movement caused by an ill-tuned e-gas controller. The Yo-Yo can be excited in any gear at any RPM if it's severe enough. The reason for the variability from car to car is still mysterious, but is most likely due to manufacturing tolerances combined with adaptive logic corrections. Yo-Yo has been identified in all past and recent MINI ECU revisions, from 31 to 36. V38, due out "in two weeks", is intended to fix the Yo-Yo. This is a viable effort from MINI, whom has been working on fixing the Yo-Yo since November '03.

In my view, the combination of bypass valve and e-gas is a bad idea. There would be no Yo-Yo if we had a traditional cable throttle. The next generation of Cooper S will be turbo, and not have this specific set of concerns.

As for a percentage of MCS's with the Yo-Yo? First off, it's not reserved for just 2004 models, as I've driven '02's and '03's with it. Looking at the Yo-Yo Registry, the vast majority are MY04, fewer are '03's and '02's are the minority. I doubt anyone can accurately project the percentage of Yo-Yo'ing MCS, because there is such a variable in amplitude, most probably don't even notice it. I've driven '04's that seriously do not Yo-Yo, so I know they're out there. Percentage however, I cannot say.

Regards,
Ryan

 

There might be multiple reasons for the yo-yo which is affected by multiple factors. Correcting one thing might help to lessen the symptoms but the inherent problem might persist. Some people have found that certain mods have helped, lets say ECU upgrade, so if you did that or some other mod that helped performance and also helped reduce or minimize the yo-yo symptoms then great.

Not every MINI has yo-yo or that problem to the same extent because we have slightly different combinations of hardware and ECU software. I guess the software is smart enough to make some changes and adjustments to our driving style and for our added mods to some extent.

 

Greetings....

After working on fixing the incredibly sluggish throttle response (and fixed it) we beleive that the yo-yo
problem has been solved at the same time. We are currently looking for a car in the greater Los Angeles area
to test our fix.... so if you have "yo-yo" please give us a call.

I wish I could reveal the fix right now, but we wan't to put the car on a dyno to prove the difference between
stock and the "fix" before releasing the info..... (and we will show you the numbers).

 

This past weekend I drove a friends 04 MCS (I also have a 04 MCS) both our build dates were Sept. 03. In fact our build dates were only one week apart (mine was built first). Both have Alta Intake w/o hose and 15% Alta Pulley. I have Magnaflow and he has stock exhaust. Both 17 S-Lite Wheels. Both of our Minis have YoYo but, mine seems quite a bit worse. Go figure!!!! BTW only other difference is I have Denso 22's he has OEM plugs. His has 10,000 miles and mine is 5,600.

 

i have a 1/04 built and I have the yo- yo............it is not too bad ............. but I thinking of lemoning my car if they don't get the a fix on it soon.


tony

 

To respond to the original post, I have a '04 MCS, 10/03 build. The yo-yo is pretty negligible. It comes on between 2000 and 3000 rpm, and is much more pronounced when the car is cold. Once it warms up, it pretty much disappears.

I don't think this is something worth cancelling an order over. I WOULD advise driving the car before signing any of the paperwork though. If you have bad luck and get a car with a severe yo-yo, you can do something about it at that point.

You should also consider that this might become a moot point, if MINI succeeds in addressing the problem before your car is built.

Anyway, as others have said, I don't think this is an issue worth abandoning your MCS over. It's just not that bad. I never experienced it first-hand, but the "bog" issue that's been solved sounded a lot worse.

Your apprehension about ordering a MCS with all of this yo-yo talk going on is understandable, but it's really not that big of a deal in the vast majority of cases.

It's not like you're about to buy a Pinto or a Corvair!

 

>>To respond to the original post, I have a '04 MCS, 10/03 build. The yo-yo is pretty negligible. It comes on between 2000 and 3000 rpm, and is much more pronounced when the car is cold. Once it warms up, it pretty much disappears.
>>
>>I don't think this is something worth cancelling an order over. I WOULD advise driving the car before signing any of the paperwork though. If you have bad luck and get a car with a severe yo-yo, you can do something about it at that point.
>>
>>You should also consider that this might become a moot point, if MINI succeeds in addressing the problem before your car is built.
>>
>>Anyway, as others have said, I don't think this is an issue worth abandoning your MCS over. It's just not that bad. I never experienced it first-hand, but the "bog" issue that's been solved sounded a lot worse.
>>
Driving before taking delivery won't help much. Mine didn't develope YoYo until 600 miles.
>>Your apprehension about ordering a MCS with all of this yo-yo talk going on is understandable, but it's really not that big of a deal in the vast majority of cases.
>>
>>It's not like you're about to buy a Pinto or a Corvair!
>>
>>

 

Hey Koopah,
Thanks for the response. I have to agree that a lot of this will come down to driver sensitivity to the issue too ...

 

I would agree with the driver senstivity issue too. For example, someone previously posted that they noticed it when 'decelerating' not accelerating. Well I never !!

I have a MCS built in 09/03 and the yoy is very much present when cold in low gears from 800 to 3,000 rpm. Why in low gears? Because the gearing smooths out acceleration so don't notice it as much. But it's still there.