2006 MCSCa, 47,000 miles

My relevant mods:
15% pulley, JCW intake, one-ball (all on for 18+months)
JCW injectors
RMW dyno tune
RMW cam and street header (installed post-tune)
Brisk 14LGS plugs

When the cam and header were first installed (a couple thousand miles ago), all was well - big power at all RPMs.

Now, for the past couple of weeks, when I hit full throttle, the car is sluggish and seems to "yoyo" in the range of 2500-4200RPM - oscillates at about 3 oscillations per second, as it slowly revs up - boost is in the 4-8psi range.. then, as soon as it hits 4200RPM where the JCW intake opens up, boost instantaneously jumps to max (about 13-14psi) and the car GOES like it should...

Thoughts? Bypass valve going out? Something else?

The odd thing is the direct correlation between the boost and the JCW intake activation... it's like something's happening with the vacuum that's kicking the BPV shut at the same instant that the intake activates (which would probably cause a momentary change in apparent vacuum at the BPV as the vacuum take-off for the intake is right at the BPV...)

Are reading boost/vacuum with a mechanical gauge as well as the ScanGauge?

Are you able to hold a steady boost(like 5psi or so) with the throttle while driving?

Scangauge only... so hard to tell...

I'm not home and haven't driven my car since I left back in October. When I left, my car displayed similar symptoms, although I don't have the JCW intake. My car will start off with the typical delay, then all of a sudden....BAM she takes off like a bat out of hell. It reminds me of old school turbos that lag. I think I've narrowed it down to the Bypass valve. Sounds like yours could possibly be the bypass valve also. I really find it weird that the JCW intake seems to open at the same time the bypass valve closes tightly. I never really read up on the JCW intake. When the flap opens, is this controlled electronically? It just sounds more like the bypass valve going out, and the fact that the intake flap is opening at the same time is coincidental. I'm going to replace my bypass valve with a detroit Tuned version when I get back, and change my belt.

Yeah, I'm thinking BPV also - just ordered a DT BPV and will install next week.

The JCW intake is electronically controlled based on RPM, but is vacuum powered - an electronic signal opens a solenoid, which releases the the flap, which is then pulled open by vacuum power, which taps in at the BPV as the vacuum source...

Probably a good time to do my belt too... for good measure.

Yes, it does sound like the BPV, and a relatively cheap fix. Please tell us how you like the strong spring BPV on an '06. From some other threads the DT BPV can be the perfect cure for early S yo-yo, but it seems that results do vary.

Also, let us know if your fuel consumption is significantly affected with the DT BPV unit.

My fuel consumption can't get much worse...

low 20's average around town, upper 20's on the highway.... but we'll see.

Check your spark plug leads....replacing them quelled my similar symptoms! My stock leads had very sketchy continuity after 5 years. Remember to use dielectric grease on contact points too. #3 coil terminal on mine was a tad corroded.

Jeremy

My fuel consumption is similar, I am sure the cam and the 440s have a role to play in those final mpg numbers. Performance does have it's price.

Oh, and get a real boost gauge, you'll be happy you did.

This is pretty much the exact same problem occuring on my 05 mini cooper s with just an intake install. I've gone over the install about 4 times and everything is connected. I'll love to know how that BPV works out.

Hey Blimey, thanks for the update and information. I had never really read up on the JCW intake and didn't know much about it. Now my questions have been answered. Like others have stated, please post results. Also, I will be getting home in mid Feb, and will be installing a DT bypass valve. Can you let me know how difficult the swap is? keep us posted.

Hey Paul,
I know this is obvious but,A retune from Jan?
Bypass valve issues-I wonder if this is what creates the strange dips on the automatic's dyno plots.Let us know how the "after"feels once the DBV is in.

Yeah... retune will happen ASAP... but that may not be soon... I had the SAME thought about the dyno issues... we'll see...

Installed a new Detroit Tuned Bypass Valve today - seems to have solved my problem. Only got to test drive a bit, but seems to work as advertised - much more of an "on-off" switch for boost - at anything approaching WOT it immediately goes to 10+psi and then builds as RPM increases - very different behavior than I was getting before.

I'll keep an eye on fuel economy - but it doesn't seem to behave much differently than stock when driving conservatively - you can easily drive around with it under vacuum almost all the time - but give it more throttle and VROOOOM...

Seems to be a nice complement to my other mods. I'm happy. The install was pretty easy - about an hour and a half plus a trip to the auto parts store to get a regular clamp for the BPV hose (makes reassembly much easier than the stock clamps). The instructions that come with the DT BPV are first-rate.

Thanks for the info. Sounds great.

That's just the kind of information I was looking for. Thanks for the details !! Hopefully your problems have been solved.

Well it seems that Blimey has had a noticeable drivability improvement with the DT BPV, congrats. Are you sure it is not somehow harder to control since the boost comes on harder/faster? I guess it is just something you have to experience to appreciate properly.

Thanks for the report on Blimey, and please do report on any fuel consumption degradation.

I'll do a couple hundred miles today and will report back. But no, there's never any kind of "lurch" into boost... it just seems to come on where it *should* come on... when you get on the throttle. At least that's what I've felt so far. I'll do some driving in various gears at various speeds today to be sure.

Paul,

Have you read up on any of Andy's postings about his VGS theory and testing? He went into a little bit of the detail on what actually causes the yo-yo and explains another method of circumventing the issue.

Hopefully more of an FYI if your further testing proves success.

Yep - read all the VGS stuff first, before I decided to go the route I went. Since my car had none of these symptoms for the first 46,000 miles, I just figured it was time for a fresh BPV in my case. But may try the VGS sometime to see what effect, if any, it has.

I spoke a little too soon - while my yo-yo is gone (completely) - there is still something odd happening... the car still has a big bump in boost at 4200RPM. I can go WOT in the 2000's and boost quickly builds to 11psi... and stays there until I hit 4200RPM, intake opens, and it immediately jumps to 13-14psi... wierd. I'm gonna go out now and do some testing with disconnecting the JCW intake vacuum line (plugging it) and try it with the intake flap close vs. blocked open - just to be sure it's unrelated to both the JCW intake vacuum mechanism and also to intake air flow.

What are the symptoms of a slipping belt? I looked this AM, and mine is no longer showing any hole in the tab... I bought a new NAPA belt and am going to install...

That may be a function of the flap. Since getting a 15% pulley, my boost acts a lot like yours but without that second jump. It will build very quickly to around 10 psi at 4k rpm then levels out into a more gradual gain for the rest of the revband. That flap might be impeding enough airflow to limit boost until it opens.

Good plan to check operation with and without the JCW airbox flappy thingie. I have permanently blocked mine open, and of course, plugged the vaccuum line. I thought I read that it opened at 4500 rpm, but I guess 4200 is close enough for government work.

Also, a slipping belt would only get worse at higher rpm, where the stress is the highest. So, that is not consistent with the symptoms. By all means though replace the belt, if you are not showng any hole, this can only help maximum boost pressure. Go for the Napa 060535, and it will be a tight fit to get that sucker on.

Well, it doesn't have anything to do with the intake... I unplugged the vac line from the intake and plugged it... same symptom exactly (surge in boost around 4200RPM - with the airbox flap closed all the time). For good measure, I blocked the flap open, and it did the same thing - so it's not an air supply issue.

I unplugged the vacuum line from the BPV diaphragm and plugged that one off also. So I'm running with the BPV always closed tight. Other than the fact that boost builds really early now, no change in symptoms - still a surge of boost at 4200RPM

Is it possible that I'm just experiencing the normal boost profile of the M45 supercharger? Maybe it's more apparent now with my current collection of mods than it has been previously?

Later changed the belt - no discernible difference. But the car seems to run really well right now... it may just be that I've never really paid enough attention to what happens in the 3500-4300RPM range... though it's hard for me to believe that.... lots of hours behind the wheel, and lots in that range...

Have you ever replaced both or either of the MAP sensors? I have seen several threads/posts in which these turned out to be causing poor performance or odd glitches in performance. If you can't find air leaks anywhere, that might be something else to check. Thing is, I don't know how one would test them. Maybe someone else could provide advice on that?

Paul, have you gotten the car re-tuned with RMW yet? I'm wondering now if maybe this is a programming problem at this point. You have a tasty collection of mods done now and they might not be playing very nicely with each other. I would almost go so far as to say you have a fuel problem, but you don't have performance head, so it's highly unlikely this is the case.