Help I'm at a loss...
 

I have an 03 R53 and the other day I noticed my boost gauge was reading low and then noted there's was a lack of pep to the car. The boost gauge is reading about 14 in/Hg when before it sat right under 0 psi. I tried to see if maybe there's a vacuum leak around a gasket on the sc, which is tricky with the electronic throttle... and last night I read about the potential for the bypass valve to at fault but it seemed OK when I checked the arm with the car off. So I am at a loss any ideas as to what I should check for would be greatly appreciated, and I apologize if this is already posted elsewhere!

bump
 

Anyone?!?

anyone?!?!
 

C'mon someone has to have some clue as to what to look for...

Slipping supercharger belt... old belt, or bad tensioner?

Is there a way to check for that or would it be one of those throw money at it situations?

Bump

We need a lot more information about the car/situation:

Year, mileage, any mods (reduction pulleys), how is the boost gauge hooked up -- electronic or mechanical.

Did you do anything to the car before this happened?
Last time the belt was changed?

As for checking tension of the belt -- very easy -- go out and push on the belt -- it should be pretty taught (no looseness).

When idling does the tensioner jump around at all -- that kind of stuff..

Give as much information as possible.

03 MCS R53
Mileage on the car is 155k engine is around 60k
CAI is the only mod it has that I know of i haven't done any mods since I bought it last year. The boost gauge is mechanical (air hose) and connected to a t under the hot side horn, also the gauge is a mini cooper gauge so I'm assuming its a factory option. I have done nothing mechanically that could've caused this or I woul have undone and retested it. I did goose it a little on interstate due to slow drivers but nothing major, shifting before 4k rpms. the belt and the tensioner were fine when I changed the AC compressor in November. so I highly doubt the belt is the issue. But a buddy was giving it a second look over the other day and noticed that there is back pressure coming from the valve cover so I checked the PCV and it was doing its job, and the PCV hose had suction to it. I am waiting on payday at this point to take it to a shop since the mechanic I talked to said he thinks it may be a dirty sensor. But other than that the only other issues with the car is the passenger door lock is not working and the drivers side muffler mount is broke, neither of which should cause my problem. I dunno about the potential for a dirty sensor to cause this issue, but I know there's something not right with the car. Any help will be greatly appreciated.

I would be most suspicious of the boost gauge being off...but lets assume it is correct for this excercise. If you were previously boosting at 14 in/Hg = roughly 7 PSI and now you are seeing 0 then definitely you are going to feel that the car is not Peppy -- actually it would downright slow.

As for what could cause a loss in boost -- I would go with the belt and tensioner again -- can you hear the supercharger whining -- is it louder or quieter than before? CAI intake mod is an area to look -- can you double check that the hose is properly connected and there is no obstructions going to the filter and/or the throttle body?

Read this on TMAP https://www.northamericanmotoring.co...-r53-help.html

As for the belt -- if you don't know the mileage on it -- you need to replace it. They stretch and to the point where the tensioner cannot take up the slack and that will instantaneously kill your boost. Not all the way down to 0 but it would pull you back..

Last thought -- and likely the most expensive -- are you on the stock crank pulley? If it is cracked then it would be a similar situation to a loose belt, the crank pulley is going slower than the engine RPMs and you get no boost - this would be very severe and frankly would be a pre-cursor to you sitting on the side of the road...easy to look at it though and "see" if its that severe.

you read the boost readings backwards. before at idle I was sitting just below 0 Id say around -6 in/Hg now its reading the -14 in/Hg so for the supercharger to kick in I'm having to get higher RPMs. That is why I think I have a potential vacuum leak. So this is why I am at a loss, Ill double check the belt and tensioner but the belt is maybe 2 years old if that cause the engine swap by the PO (which I have all the paper work from the work that he had done).

Since you are seeing this at idle -- I again go back to the supercharger not spinning. So I re-affirm my stance on check the belt, crank pulley tensioner.

The belt age is kind of on the brink in my opinion but more importantly how many MILES are on the car I change mine every 20k miles...or 2 years whichever comes first.

155k on car something like 60-65k on engine, id have to do math and i don't feel like crunching numbers atm... Ill go double check the belt again but could it happen so instantaneous?

I'm not answering any more questions Until you go check these things - it's frustrating....

just went outside and checked the belt, tensioner and the pulleys were moving and everything checked out fine.

How did you "check" all of these things? Let's go back to bypass valve. Did you try the zip tie test? Just pushing the arm back and forth won't tell you anything and without pulling it out, you can't even tell if it is closing all the way. Same thing with the belt, simply looking at it won't really tell you anything.

When I checked the BPV I did the push test and I zipped tied it, and had the wife run the throttle so I could see if it was opening and closing which it was. I gave the belt a look over, but I did crank the car to watch the and see if the tensioner was bouncing and I even tested the tension on the it with the belt tool. My response will most likely be delayed I have to go get ready for work, but I will try to reply as I get the chance (beauties of working healthcare...)

Okay fine...did you pull off the inner fender liner and take a real solid look at the crank pulley and try to wiggle it back and forth?

Other than that - I feel like a failed sensor would throw some sort of error code.

Our supercharger system is pretty straightforward belt driven faster spinning = more boost so I'm not sure where to go with it.

Didn't have time or the means to jack the car up and pull the fender liner at my house. But I may try that this weekend.

So for grins and giggles sake let's say the crank pulley is fine and dandy as is the belt, what would be the next thing to look for?

Your really pushing my thoughts in this one - I would have to say tensioner but if that's fine I would think some sort of clamp or hose. The couplers from the supercharger horns can get old and leak - which would leak some boost into atmosphere but it seems like you are losing TONS.

What is the MAX boost you see when you are on it?

When I get on it (4k+ rpms) my boost reads a normal at around 15 psi. But as soon as I let off the throttle it nose dives. If I didn't know better I'd think I have a turbo'd mini, my thoughts are that I have a bad hose or leak on the cold side that I can't see without pulling the intercooler. Another thing with a cold air intake should I be able to hear it suck the air in? Because when I had the wife giving it gas while in was trying to find a potential leak I could hear it with every rev. And I'm still not sure how these potential issues could cause back pressure under the valve cover... but I am new to minis and super chargers... and I apologize if there's typos I'm on my mobile. And I appreciate the help!

15 Psi is very hight for a stock mini so - the car must have a pulley on it. As for why it nose divss when you come off throttle - it's supposed to do that - I am pretty sure that's the exact function of a bypass valve to bypass the SC. If you are seeing 15 PSI then you definitely shouldn't be complaining about not feeling boost. Can you take a picture of the end of your supercharger where the belt is attached. I have a theory that someone put a stock belt on your car and you are using a smaller pulley which would lead to some serious slipping at high rpm. Also can you look at the tensioner and tell me how many holes you can see. http://www.pelicanparts.com/techarti...mall/Pic10.JPG That is what I would like you to look at ... You should only see 1 when the belt is on there.

as for hearing air being sucked in - yes for sure. With an intake you can hear it being sucked in quite well-listen below.

I'll see if I can see that when I get off work here in the next hour or so. So with the belt on I should see that first hole, and just because I don't remember what it looked like when I did take the belt off when I changed the ac compressor what if I see no hole? Just a curiosity question.

Belt has stretched or wrong belt used.

So assuming from the amount of boost I do get when it kicks in that I have a reducer pulley on the super charger how do I know what size belt to get? Or is it the same belt for a 15 and 17% reducer?