Hope this is the right forum for this...

I have an 06 MCS with a 15% pulley and yesterday I installed a Detroit tuned bypass valve, new belt, cleaned throttle body and my IC, and did the VGS Mod found herehttps://www.northamericanmotoring.co...ystem-vgs.html. The VGS mod was done after (problem remains with or without the mod) I had drove the car and noticed very prominent Yo-yo feel at moderate throttle (seems to happen more between 2500-3500 rpm) but if I go WOT the car drives like a bat out of hell. Is there something I could have done wrong? My car didn't behave this way before the new bypass valve. anything I should be checking? My only thought that I think that could have happened is the intake tube going to the supercharger (plastic tube the throttle body bolts too) is slightly off allowing air to bypass the throttle body. but in that scenario wouldn't the car idle rough? (which its not) any input on this would be great kinda out of ideas where to look.

Thanks in advance

 

I did the VGS mod on my '06 MCS, and it introduced a slight yo-yo issue at low RPM. The mod was really intended for the '03-'04 MCS's and is really not needed. Whenever I get around to buying the DT BPV, I'm taking the mod out.

You DON'T need the mod with the DT BPV. It's supposed to correct the problem by closing all the way and having a better spring.

 

Un-do the VGS mod....the combo of the two...bypass valve with stronger spring and the VGS mod is interacting.....
Some folks love the DT bypass valve....so say it makes the car hard to drive smoothly....that is why used ones turn up..it is a love it or Hate it thing. Also check the vac lines....some can be Very hard to connect correctly with the VGS mds or bypass valve install.

 

I was just about to post exactly the same issue:
I installed the Detroit-tuned BPV with exactly the same effect:
Sort of yo-yo or hesitation between 2800 and 3500 rpm at partial throttle.
At WOT it goes like stink.
I did not do the VGS mod.

I'm guessing the spring on the BPV is too stiff, pressure builds too fast and the car responds to prevent detonation...what would it do? Adjust timing? Or dump more fuel into the cylinders? I'm thinking/hoping it's the latter as I've been experiencing really bad fuel consumption since this problem first appeared.

 

The OP's car does this with or without the VGS mod.
Mine doesn't have the VGS mod and does the same thing...plus I went from 24mpg to 20mpg over my normal daily route.

 

I'd still venture to guess both of you have a vaccuum leak. Check the plastic intake tube connection to the s/c and all vaccuum lines around the intake. make sure the BPV and TB etc are all tightened to spec as well.

 

Thanks. Will do, is there an easy way to check the connection on that intake tube? It sort of goes off into an abyss - if you know what I mean. When I put it back in place after the install I wiggled it around until it was sort of stuck in place/stable...and everything else lines up perfectly with it, so I guessed/hope it was ok.

 

It is a tight fit, I actually ran mine with the bolt tab broken off it for a while without any leaks either. You might have a broken tab if you popped yours off and shoved it on without removing it. To really get at it you need to put the front end in service mode, but you can use flashlights/mirrors to take a look down there and just make sure it's fit snug into the s/c intake.

 

if you eliminat the possibility of a vaccum leak, the oscillation may still be there. I seem to write about this every month or two. Latest descriptions of what happens are here and here. Happy reading!

Matt

 

Thanks! Is there any way that the BPV or a vacuum leak could cause a pretty significant deterioration in mpg? I went from a consistent 24mpg to 20mpg for the past 6 weeks after fitting the BPV.

My initial thoughts were the my O2 sensor was going bad - but that feels like a bit too much of a coincidence.

 

A vaccuum leak really shouldn't drop mpg's almost 20% like that. You can reset your ECU and make it re-lean your fuel map as a long shot. It could be your o2 sensors, or a bunch of other air/fuel realted stuff. Check your throttle body and the electrical connection cause that's the closest thing I can think of that you touched that can affect mpg like that.

 

The DT bypass valve will cause a reduction in MPG...they even say it on their website....you build more boost, so it takes more gas!! Most folks usually say they loose about 2 mpg. So maybe once you adjust you driving style, it will go up again!!

 

Thanks for the info - 2mpg...close to what I'm seeing...well, sort of close...I also installed an OS Giken LSD at the same time, so my driving style has been a bit more aggressive lately ;-)

 

Matt brings up a very interesting point....
The fact the yo-yo mostly went away when the factory bypass valve was made slightly stiffer and through a bunch of software updates make me wonder if the carcmay have a very old version of software....or if one item is updated, and not the other (bypass valve/software) if the ossilation my be induced by the interaction of the two...
So many gen1 garage queens are comng out of hiding, I wonder if some, if not most of them have EVER been updated software wise.

 

My car is an 04 JCW. I installed the 05 injectors and airbox about a year ago - and had the software updated at that time too -> I guess that would have addressed the yo0yo issue...?

 

Depends...the software that fixed it fo most came out in mid 05, even into 06...similar timeframe for the reworked bypass valve with a slightly stiff spring from the oem...I think that stated with model year 05 cars, but I'm not sure.
Most folks usually had the yoyo go away with computer resets/adaptation resets for a short time...But it was never really fixed till both items were common.
I'd try to reset the computer...no harm in trying, then check for vac leaks too.

 

Th fact an 06 is reporting a yoyo is odd...as said before, look for vac leaks...

 

that MINI actually ever totally eliminated the problem, it's just that the frequency of those that report it is a couple of orders of magnatude lower. But it's not zero.

Matt

 

My 05 had the same flat spot with the DTBPV...with or without the VGS. All the vacuum connections were zip tied. I talked to Chad @ Detroit Tuned and he said it's just in the ECU programming.

But....just got back from a tune with Jan from RMW...that fixed the flat spot (and also made it smoother and more powerful all over).

 

I reset the ECU and it seems much better this morning...Still has the usual flat spot at around 2800 rpm (I know I can tune that out)...

I'll see if it stays this way, the improvement might just be due the the cool morning we had in AZ today (only 90 degrees when I drove to work)...the problem always seemed worse when driving home in the afternoon (115 degrees).