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Old 09-22-2015, 11:48 AM
MontanaRob MontanaRob is offline
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Default B7 Supercharger system unsolved issues

Hi, I'm a newer owner and have developed a particular problem that has stumped 3 good mechanics. There are so few of the supercharged models out there that it seems no one is an experienced expert in this system. I have 2 main issues that may or may not be related.

1) 07 and 08 were supercharged years (USA). My 07 is making what I would call a loud chug-chug-chug sound/feel as you let off the gas after you are over 3k rpm or more. It is louder at higher rpm and follows the engine speed as it slows until you cant hear/feel it under about 3k. To me it sounds like backpressure from the sc but I swear I don't recall hearing it before. If parked with hood open, you can see the intake piping jump around significantly as it chugs down the rpms. Most sc and turbo systems have a blow off or bypass valve to allow excess pressure to escape when you let off the throttle, but my understanding is that Alpina's system is different and relies on the Valvetronic system and pre/post sc butterfly valves to modulate that pressure pre/post supercharger compressor without a "bypass valve".

Charge air pressure regulator (pre supercharger)
http://www.realoem.com/bmw/enUS/show...17#13547966233

Pre-intake manifold temp/pressure sensor (which is just upstream of the throttle and butterfly valve assembly)
http://www.realoem.com/bmw/enUS/show...18#13627966237

See this article here where it explains that.

http://myautoworld.com/BMW/cars/bmwc...07-alpina.html

(excerpt for convenience)
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"Accomplishing the basic goals – this high efficiency under part-load conditions but a high level of boost for maximum power – required far-reaching development of the engine's electronic controls and a new concept in power regulation, namely:
•A pressure regulator before the supercharger, which maintains pressure before the engine throttle at atmospheric.
•A throttle between supercharger and engine that holds pressure in the intake manifold at 50 mbar (1.5 in. Hg or 0.735 psi) less than atmospheric.

These two elements allow the engine to be controlled by Valvetronic up to the point where the intake valves have reached their maximum opening via Valvetronic; it also helps minimize any pumping losses in the supercharger, which under these conditions is essentially "coasting." At this point, the pressure regulator before the supercharger becomes the engine throttle, responding to the driver's accelerator-pedal input and regulating the supercharger's boost accordingly. Sensing and regulation functions to execute this strategy are included in the engine's electronic control system. This entire system was developed, and is patented, by ALPINA.

The supercharger itself is a new development. It's of the Radial or Nautilus type, not a brand-new concept as such but now appearing on an automotive engine for the first time. It had been patented by ZF in the 1980s, but only recently have metallurgical advances made this actual vehicle application possible. (In connection with the B7, ALPINA has several patents pending.) At full boost, the supercharger delivers a positive induction pressure of 0.8 bar."
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Note: I usually get a single puff of light smoke come out the right front when I come to a stop. Not out the tailpipe. (This has been confirmed as a valve cover gasket related seepage onto the exhaust). The valve stem seals are also starting to pass a little oil at 150k miles, which is a common issue but this is not a major concern yet.

2) The other main issue is that when you are BARELY on the throttle (like just touching it to maintain constant rpm), the car stutters and hesitates almost like a misfire feel). This is more frequent when you are on flat ground or downhill on cruise control (barely on the throttle to maintain speed) It will do this in any gear at any rpm and it more noticeable at higher rpm. Other than that runs great and hard!

This is an N62 engine platform but with some different Alpina-specific internals and sc components (detailed in the link above).

Things done/observed lately:

Changed plugs (correct NGK high heat kind) - no effect
Changed ccv diaphrams - no effect
Changed rubber seal plates for eccentric shaft sensors - no effect
Did the electronic reset of the adaptive transmission (step on gas for 25 sec while ignition on) - no effect
Intake piping is clean and clear (except nominal oil from vapors pulled in pre-supercharger from crankcase ventilation tubing)
Mechanic found bmw vacuum code and cleared it. No other codes or errors. Was not specific enough to locate if at all current. Manual search indicates no broken hoses, pipes, etc in crankcase ventilation or otherwise.
Vacuum test via oil cap with no leaks
SC operates fine, no noises or leaks
Transmission was serviced (no effect)
Does not burn significant oil
No codes.

I feel ok driving it but the hesitation issue is a pain and it is not normal. Wondering if the backpressure can be damaging or maybe that Valvetronic system is not working the exhaust valves properly.

I am not sure if the low-throttle "jumpyness" is related to the chug problem (which reminds me of the sound and feel a jake-brake on a semi tractor )

Any help or knowledge of boards with deep expertise would great, thanks.

Last edited by MontanaRob; 09-25-2015 at 11:39 AM.