I have a 2003 S I bought from the original owner in 2010. (60k miles currently)

Lately the car is much quieter during acceleration and doesn'thave the power it once did. It drives fine, no codes and no overheating, just can't hear the SC spooling and doesn't have the punch it used to. I removed the hoses and looked at the bypass valve today and didn't see anything strange (though I have no idea what I was looking for!) I've read there is a diaphram that may cause something similar?

Anyway, any input on what might be causing this is greatly appreciated. I am mechanically inclined though I usually work on my Jeep - haven't had any trouble with the commuter before this!

 

As the SC is belt driven, it is always spooling up if the engine is turning. The bypass valve would be the most likely culprit. Haven't played with mine, so I can't give you any insight on failure modes.

 

I agree; I don't think I have the language to describe what I'm experiencing very well...

All the more curious though that I'm not hearing the SC (not just me either - a friend commented on it recently) and I don't appear to be getting any benefit from it. In addition to the bypass I'm wondering if a loose belt could cause this to happen?

 

As Eric said, the SC is belt driven and is spooled the minuet that you crank the engine. Most likely the bypass valve has gone bad as this is a known issue. The belt may also be going, but the SC would still be spinning.

 

Check the bypass valve...ir can be ziptied closed for a few days to test it...this will decrease mpg, and will not cause any real power increse unless it is broken.
what you might be feeling is a combination of heat soak (due to intercooler placement) and the associated timing pull by the co
puter to prevent detonation from the hot intake temps....many folks are kinda supprised to find the power differance is kinda like night and day summer to winter.
Does your car have a pulley? If so, the plugs should be changed, like a jcw frequency wise, so about every 30,000 miles, unloke the s where it is much longer.....but the higher preseures/temps with a smaller pulley is tough on the plugs.

 

Two things happen in the bypass valve...
The spring breaks internally..leaving it open....or the vacume line to it leaks/falls off....
The purpose of the bypass valve is to dump sc preasure at low (idle) rpms to reduce engene load, improving rpms....a stiff spring and/or more vacume equals closing st lower rpms....many folks can kinda feel the closeing of it...the accleration changes from **** poor to nice around 2000 rpm....what some folks associate with a heasitation or a bit of yoyo....very pronounched on some cars, barely noticeable on others based up different software, etc.
The sc is a bit if a wear item....so beyonf checking your airfilter to ensure you are getting clean air....i know when i was in colorado i used to go through airfilters....a bit bit of dirt/sand could realky hurt the rotors, resulting in a quieter/lower boosting sc.

 

Hey Heavy,
I had the exact same problem last month. Speeds around the neighborhood were ok until I hit the highway, heard a "pop" and experienced a huge power loss across the entire power band. My guy found that the diaphram on the bypass valve failed and was not allowing the valve to open fully hence the power loss. My engine light did not come on either.
It ran me about $400 after diagnosis, new bypass valve and installation.
Tally Ho!
Alfred
2003 R53 w/ JCW

 

Any updates heavy18?

The belt would be unlikely. If it were loose enough to not spin the supercharger, it would be loose enough to not spin the alternator, or the a/c compressor, etc. Also, you'd notice it burning rubber if it were slipping that badly.

If you have an aftermarket pulley on, perhaps the screws could be loose such that the pulley is spinning but not gripping/turning the shaft of the s.c. Again, pretty unlikely as nothing would prevent the pulley from walking itself off the shaft thus tossing a belt. If anything a visual inspection would probably notice a lot of lateral movement from the pulley.

Detroit tuned sells an upgraded bypass valve with a stronger spring for your model year:
http://www.detroittuned.com/shop/?productID=179

Poke around with the search and you'll be able to come up with a thread on removal of the bpv too.

 

Yep, the bypass valve spring failure seems very common...I had the same problem with my 03' MCS.

I installed a Detroit Tunned BPV.....problem fixed!! It seems to come into the boost faster also, which was an added bonus!!!

 

Thanks for the replys. Work heated up this week so I haven't had a chance to get back under the hood again, hopefully I will tonight.

I have the stock pully on it so that should not be an issue. I did do a visual inspection of the belt and top pullys and didn't find any smoking guns there so perhaps that is a dead end...

I'll grab an air filter today and swap that out as well as the plugs just to check those off the list. I could also open up the bypass again and check the hoses, but everything looked good when I was in there last time... is there any way to determine if it is functioning other than replacing it?

Also, I don't know what kind of mileage I should be seeing, gut I always get between 27 and 29 MPG. (Calculated at the pump every fillup)

One more small bit of info, it actually has a little over 63k miles and I haven't done any scheduled maintenance since 30k mi... I'll look into what is typically done at 60k.

 

Can you tell me how to zip tie it closed? From what i remember when I took the hoses off to look at it, I'm not sure jow to accomplish this.

 

When the motor is off , look at the bypass valve and the little arm that comes out of the side of it. You should be able to rotate the arm, and then when you let go it should snap shut with some decent force. If it doesn't snap all the way shut when you let go of it, or it's very weak.....it means the spring inside the valve that is supposed to close it is not working. Mine had a broken spring ....and it was very easy to see that it was broken.

You can try zip-tieing the valve shut...but it's a royal pain trying to get a zip tie down in there. All zip-tieing the valve close does is to keep the valve all the way closed under WOT....just like the spring is supposed to do if it's working correctly. It's just another way to check the valve......but if it's obvious that it's not closing all the way, then you found your problem.

 

One more tip...
if you do plugs, PLEASE use a tourque wrench!!
The mini s is known for spitting them out.
I have swapped plugs in many aluminum heads no issues, did the plugs in my mini...about 15k later my mini guy double checked the tq, and one had loosened to finger tight....so was getting ready to get blown out. So tq it down, then check it a few thousand miles later. Ngk imo seem to be a good plug on a mini...
Your mpg is about as good as can be expected on a 100% stock gen1 s...most do worse due to driving habits.i do about the same when driven nicely....but have modded and tuned, but it just proves mpg is more about the hp you use than the hp you can make if the car is running the right maps (tune).
mini went from a pretty weal bypass spring in 2004, to a stiffer one for 2005 production....there is a modified factory one from detroit tuned a stock valve with a stiffer spring atound too...some like ut...some see too much mpg loss and loss of smoothness.....if it is the orgional valve, it is likly tge spring has failed or even the interior might be not seating right, thus not sealing. If you do dig deep enougg to look at it, it might be worth just swapping it out...but like i said, it can be wired/ziptied shut if the issue is not internal to verify it is the issue (spring) to save a $.....just costs time to openen it up a couple times.

 

Another tip for changing the plugs.....make sure the motor is 100% cool (room temp) before you attempt to unscrew the plugs. The problems I've heard with people stripping out the threads have always been when guys have tried to take the plugs out while the motor is still hot, or even just slightly warm.

 

Will do, I have one, what should I torque to? (online I've seen postings for 16 ft/lbs and 21 ft/lbs... )

Noted.
I plan on doing this one thing at a time when I get home so that hopefully I can identify the culprit. I've unplugged the battery while I'm at work so the ECU will reset (read that elsewhere...) I'll see how it drives going home. Then I'll change the air filter on my way home. If it doesn't cool down enough tonight I'll change the plugs in the morning.

The spring on the bypass seemed pretty good when I was looking at it - it would snap right back into closed position when I opened and released it. Can I disassemble it to inspect the diaphragm? Probably just worth the $120 to get the Detroit tuned one...

Another thing, I've never replaced the SC belt or serpentine, so I should do that I suppose. Are these belts doable for a DIYer? Like I said, I'm moderately mechanical, but haven't worked on smaller engines much. (I mostly wrench and weld on the jeep) I'm considering going to a 15% pulley as well, but haven't read into that at all.

The parts store says the fuel filter is incorporated into the fuel pump? that seems like a crappy design...

 

Fuel filter fits over the fuel pump...and can be changed...must lift up the rear seat to get into the fuel tank.

 

Well, on the drive home I didn't notice any change in performance (after resetting the ECU) but later that night I seemed to start hearing the SC a little more.

Today I changed the plugs and that seemed to add some pep - just a little. Next I changed the serpintine belt, that seemed to do the most in terms of bringing back some of the whine I'm looking for from the SC.

Then I changed out the air filter, and I'm embarrased with what I found life has been pretty hectic the last 2 years, and I was possitive I had changed the filter... but now I don't see how that is possible:





So as you might suspect, the Mini was pretty happy to have fresh air! Sounding better and driving stronger for sure. As a final item I threw some Seafoam in the tank, but that will take 2 weeks to work its way through.

I'm still not convinced that I'm at full potential yet, but I'm content to drive it for a few weeks and see if I change my mind about that. I still want to install a Detroit tuned bypass valve - maybe next month.

Anyway, thanks for all the input!

 

Make sure the crank pulley is in good shape.

Also with 60k and that age I would definetly upgrade the plugs wires and coil just for maint.
http://www.waymotorworks.com/wmw-ignition-package.html

 

Geez thats one dirty filter.. btw, if you want to check if your bypass valve is working properly simply accelerate your engine right before redline while in gear and let it decelerate on its own.. If your bypass valve is bad the car should go into "limp home mode" at around 4-5k revs.
Take a wild guess how I know this...

 

I had a broken spring on my BPV, and it never went into any kind of "limp home mode". It just didn't build much boost.....