I just installed a few mods on my 06 MCS.

New:

Mini-madness 15% pulley
Giac ECU (no injector file)
JCW exhaust
Denso IK22 plugs
MINI Blue ignition wires

Old:

Myminiparts intake

Now all of a sudden I am getting the damn yo-yo effect at 3000rpms, ~ 5-8psi. With the boost gauge I can see the needle just bounce around at partial throttle.

At WOT, everything is fine and dandy though I am not making as much boost as my 04 MCS which has the same mods other than a UUC exhaust. 06 is showing about 12-13 psi max whereas the 04 is putting out just above 15psi. Faulty BPV?

I definitely felt the yo-yo the first day I did the pulley install and not sure if the GIAC tune has made it more evident...But I usually don't drive this car (the wife's) but I have driven it for the past three days and the problem is definitely there.

I took off the intercooler today, checked the throttle body bolts (there were a bit on the loose side) and made sure everything was night and secure (clamps, IC boots) and the problem remained.

Nor am I having this issue on the 04 MCS so go figure.

I'm going to try VGS to see if it fixes the problem.

I also tried to adjust the bpv but the damn adjustment screw was red loctite and would not budge.

I checked my belt tensioner pulley and it seems to be fine - not moving at all. Belt tension is good (installed a Gatorback 060537 belt a few days ago).

So my plan of attack is as follows:

1) Double check and just make sure I got the right GIAC file for my mods

2) VGS if 1) checks out

3) DT BPV.

Are other cars all of a sudden developing the yo-yo effect??

Any other suggestions?

 

Lord I had the yoyo real bad and the Detroit BPV helped but GIAC got rid of it completely. So I am not sure what combo caused yours but it seems different then mine.

 

I have both the GIAC and the DT BPV and still have the yo-yo. I can't figure it out either. Mine seems worse since I got the GIAC.

 

Install a 0.0295" restriction orifice in the BPV vacuum line. Worked for me in my '04. Cheap too.

 

Yeah very strange. This is exactly the conflicting kind of info I've found. Some say it's the ECU tune, some say that the ECU tune cures it! Ack!

How did you come up with .0295"??

 

I never seemed to have any problem with the yo-yo...but I just had my bypass valve replaced at the dealer and there is definently some yo-yoing going on now. Can only really feel it in 3rd gear, moderate acceleration, around 4k RPM. It's kind of annoying, especially since I never had it before...grrr

 

It is a standard drill diameter, maybe a #69 or #70. I bought a BPV, put some microswitches on it and measured the step response closing time with different restriction diameters. Response of the valve without the restriction was around 25 ms. When I got a closing time around 200 ms the yo-yo stopped - worked out to be that drill size. This was reported in the "yo-yo chronicles" thread of 2004.

 

I had Yo-Yo occasionally on my 06 after installing the 15% pulley, after doing the VGS mod it took care of it.

 

Ok I just did the vgs mod and yee haw, the yo-yo is gone!

Thanks for everyone's input.

 

vgs ?

 

That's what I'm getting with the DT bpv. Mine happens when at vaccum or at 0 or just before I hit the boost in 2nd or 3rd gear in moderate acceleration. I never had this before the BPV but now it's definetely there.

 

Vacuum Gain System - it's a method of changing the source of the vacuum used to close the bypass valve in order to eliminate the "yo-yo" effect and to better keep the bypass valve closed under boost.

The big thread about it is here.

 

My yo-yo disappeared with the DT bypass valve. It's niiiice /borat

 

I think this is an interaction between the drive by wire system and the BPV. This makes it Mini SW version dependant as well. I don't think anyone has done a matrix to see what Mini SW is worse than other, but in general, the earlier versions of SW had it worse than the newer.

That said, there are tons of ways to skin the cat. Anything that makes a difference to the BP response will effect it, as will anything that messes with the drive by wire code! I think this is why we get so many different bits of inforrmation about what makes it better or worse.

Also, many have found that some mods will make it better or worse, and while this is baffling, I think it all makes sense if you think about how it affects the drive by wire system.

Matt

 

Based on a discussion in the Boost thread and what Dr. O said about checking for leaks. I did this even though I was under the impression, from several reputable vendors, that it was an ECU issue. I have the DT BPV but no VGS. Weekend before last I pulled the intercooler and visually checked everything. The only issue I found was the hose connecting to the fuel rail(?) where the VGS taps into. It seemed a little loose so I reseated the hose.

That cured the problem. I noticed right away the next morning when starting the car. The idle did not dip and stutter for a few seconds like previous mornings. For the next week it was smooth sailing. No dead feel under normal throttle around 3k rpm. Then a few days ago it started slowly creeping back to normal. It's now back to the way it was.

Tonight I repeated what I did originally to see if this will cure it yet again. If so then a new hose may be due. It did not seem loose this time like last but I'll find out in the morning. I'll post the findings around lunch tomorrow. Maybe one reason the VGS mod makes a difference for some is because it replaces the factory hose on that connection with a different one. Maybe the factory hose does not supply enough grip to stay like most rubber hoses do in the VGS mod. I have no idea.

 

THEN it's an ECU issue! OR a sensor issue, or a TB issue, or who knows, but an issue for sure! But I've found that the factory hoses are pretty good, as they engineer the connectors to take both the boost and the vacuum. But for my VGS install, I used standard hose, but used wire-ties to really hold them down. The standard rubber vacuum hose isn't to good agains pressure, as the hoses expand a bit.

I haven't really seen too much posted about this. Get as tight a vacuum hose as you can get (mine arn't that tight, hence the wireties), and wiretie it anyway!

Matt

 

SB, if we don't have the VGS is that connection to the fuel rail worth checking? I'm not sure of the diff. between how it's connected stock or with the VGS. I pic or two would be nice. The stumble at 3K is bad on the streets for me. I might just need a little back pressure on my exhaust side. If a zip tie on a vac line would cure it that would make things a lot easier.

Thanks

 

There are lots of theories on the cause of the stumble, but backpressure has nothing to do with anything on this one! There is some evidence that poor header design can contribute to reversion, but other things create the "stumble" as well.

Search on "VGS" or "Vacuum Gain System" (Wonder where Andy came up with that name!) and one of the mother of all threads has lots of graphics on vac hose routing etc.

Our minis use somthing called a "rising rate fuel pressure regulator" that takes a vac line to the base of it to raise fuel rail pressure as boost climbs. (If you think about this, it's so you can squirt enough gas against the pressure of the boost). If the vacuum line comes off here (and I've heard of a few that have, don't really remember if any were the stock hose) you loose this feature so you start to run leaner (not all bad on a stock tune) but you loose boost/vacuum from the open line, and this creates all sorts of drivability issues.

If you really want to attack this issue, first you have to know that your car is sound to start with. This means that you have to make sure all the lines are tight, and you don't have any leaks anywhere in the intake track. A shop with good sniffing/intake tools can be a big help here. One guy with problematic vacuum readings got his intake track pressurized and found a couple leaks at gaskets and a couple welds on his Gintani that needed some work....

Anyway, issues like this take a reasoned troubleshooting approach.

Also, I'm writing an article on exhausts for the next MC2. The single most miss-understood term in exhaust function is BACKPRESSURE! It's all a BS myth! what you're really talking about in torque development with an exhaust system is exhaust velocity, and for a lot of reasons these two concepts get put in the blender and pureed together into a milkshake of pure BS. Doesn't taste good. (guess you can tell you hit one of my nerves!) To find out more about this, you'll have to wait for the article!

Matt

 

I used a shop vav on blow (cleaned up of course) to check for leaks on my turbo bike, it will run up to about 3lb boost! Use soapy water ,look for bubbles.You have to cobble up some kind of adapter with duct tape and whatever.

 

Dr O, that was a compliment. Instead of spending a lot on software I was able to cure the problem for free within 15 minutes because of your post.

This morning on the way to work and also lunch my MINI pulled from 2600rpm to 3200rpm as smooth as a babies butt. Not hiccups at all. Though this morning just after starting there was a very mild drop in rpms and stutter but nothing compared to what it was like.

I'll swing by the local Subaru performance shop and speak with them. They should be the most familiar in this area about boost. See what they have to offer in hoses before I purchase an OEM hose. I'll also see if they can leak test it after the hose is replace. Though I'm sure my culprit has been found.

 

I like to help, and glad it was of some service...

Not surprising about the stutter. If there was a vacuum leak, it shifts the TB position at idle. The ECU has to relearn the idle set-points.

Now, that will be $200!

Matt

 

This part is very interesting to me. I'm taking my car over to Niello next week to have them do some snooping to look for anything that might be disconnected/non-functioning/leaking, etc. I'm getting low boost, yoyo-ing and uneven acceleration and driveability. Also getting pinging if I really put my foot in it. I printed the above paragraph out and will have them check this hose out. They'll be poking around the area anyway. I'll follow up with what they find.