Hey guys,

I was driving on the highway today and noticed that at high rpm the car seemed to have a flat spot and also noticed the boost drop on the scan gauge. Most boost I see is 13.4 PSI...then it dropped to like 4.something.

No check engine light...and car runs fine otherwise.

Is this early indication of supercharger failure? (I have one sitting on the shelf) Is this indication of bypass valve failure (also have one on the shelf), early indication of super charger silicone coupler failure (again have them sitting on the shelf).

Thanks for the input.

 

I would doubt bypass valve since you are getting boost, not supercharger failure since your making boost


I would check the couplings for the intercooler and your belt tensioner

 

Belt slipping would be a good place to start. Check that you have proper tension on the belt, and that your belt is in good condition. I wouldn't completely rule out BPV just yet, but check the belt first.

 

Would be easy to zip tie the bypass valve and go for a drive ..
Remember, it does use vacume AND a spring...
I'd look at it...I would expect a leaking ic coupler to just be a pleatu in psi, not a complete loss...
Is it a mechanical guage or just a odb2 reader getting the info from the car for the boost?

 

Hey Zippy, Just the Obd2 reader scan gauge ii with the custom "programming" I only looked at it because I felt a flat spot...and noticed the wine of the supercharger really change tone. I'll take a look at the spring and tensioner tonight. Should mention the following: 2003 stock tensioner at 102k, 15% pulley installed at 67k, replaced belt about 10k ago with gates reduced length belt and stock crank pulley (I know I've been gambling). I have a pulley from a 2006 again sitting on the shelf...haha I have a lot of stuff sitting on the shelf - no tensioner but I do have the power flex bushings for the dampener...oh why is it -10 out

 

One thought...
If the t-map is getting flakey, it would send bad info to the computer and the guage...
So after you do the simple stuff...might want to try to clean, test or if it drives you nuts, try swapping it ...guess you could borrow a mechanical boost guage and go for a drive with a tempory hookup...and see if the boost drop is real or not...first, I would look at the stuff helix is suggesting...checking the tensioner, etc...
Since you said you think you hear a "whine" change, I'm pretty sure helix is right, or the bypass is piping open...might want to look at the vac line attached to it...

 

Hey guys,

So update -- the behavior is a bit intermittent. I jumped on it coming out of a toll booth this evening coming home and it held boost all the way up to 14psi. First time I've seen the gauge read that high actually.

I lifted the bonnet and checked the tensioner when then engine was running -- no jumping around -- tiny bit of movement that I could see. Turned off the motor and touched the belt - seems to have good tension - not sure how tight its supposed to be BUT there wasn't any slop.

I reached down and touched the BPV -- it had good push on it and snapped shut when let off of it.

So follow up questions: is there such a thing as a stuck BPV? Its pretty cold here -- our high for today was 24 degrees. When it was behaving well - the temp was close to the high end.

I'll be doing quite a bit of work in the spring (next month if it warms up enough):
1) Crank Pulley
2) Intercooler Couplers
3) OEM BPV (While I am in there)
4) Tensioner Bushings at the least -- maybe the whole tensioner
5) Valve Cover gasket
6) Oil filter housing gasket
7) Oil cooler gaskets

ZippyNH as for the Boost gauge -- might be time to finally pony up and get one -- looking for the most stock looking setup there is. I don't think they still make the stock dual gauge setups but i haven't done much research yet.

I initially got the scanguage when I was having issues with "overheating" boiling coolant which I later traced back to a bad low speed fan -- I ran the AC constantly for a year until we moved to the burbs and I had some time, space and confidence to change out the fan. Might run water temp and boost.. although given our lack of any real oil pressure warning was thinking Oil pressure might be the better bet.

Thanks everyone for the input.