Hey guys,

We are the second owners of an '04 Cooper S JCW. The original owner installed an Autometer boost gauge. It would read about ~11psi under boost. I've noticed for about the last week or so it is no longer reading that level. It seems to only be reading 5-7psi on WOT accel, and maybe 10psi once you hit ~6000rpm. It would pretty much always hit 10-12psi under wot Accel before. I don't know if the gauge isn't reading properly, or if the car is just producing less boost than before. What controls the boost pressure? This is the first super charged car I've ever owned. Does it rely on some sort of waste gate or something like the turbo cars? At some point I'm going to hook up a different gauge, but I was just wondering what could cause the lack of boost if it is actually producing less boost.
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thanks!

 

there is a bypass valve that dumps the boost when you let off the gas under vacuum.
https://www.waymotorworks.com/oem-mi...e-r52-r53.html

Otherwise the boost is just mechanical as the supercharger spins.

 

If you have leakage in the system your boost would suffer. I found that the clamps holding the bypass valve were leaking. I pulled them off and put worm drive type clamps on.

How good are you at turning wrenches?

 

This can be the reason, or just the vacuum line can be bad or off:

It is the boost bypass valve, that opens and stops the supercharger boosting during the idle time. It can get stuck open, or partly open. They are about $70.

 

I appreciate the help. I will look into this valve. I am completely competent with working on vehicles, I just don't know too much about this car. It is fairly new to us, and I'm still learning about it.

 

Replacement of bypass valve:

Make sure, if you are going to do this, that vacuum lines are in good shape and not leaking vacuum, as replacing the valve, my not help at all, with other leaks.

Point #2: Make sure the harmonic balancer on the crankshaft has not come apart, as slipping with reduce or even stop the supercharger from working. This is a common problem and I have had to change several for this very reason. Aftermarket fluid one is what I use you can see it on my post in the gen 1 jcw section. The failure of these is about 100% after 100K miles.

 

I'm going to dig in to look at all of this. What am I looking for with the harmonic balancer? Would it be obvious if it is going bad?

 

On the crank pulley/harmonic balancer, you remove the drive belt and see if you can push the pulley in so that it hits the motor. You can also jack the passenger side wheel up and see the pulley running. There is recent thread where the guy posted a video of the wobble.

https://www.northamericanmotoring.co...on-my-r53.html