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Re: high boost stumble

In a message dated 12/27/99 1:00:17 PM Eastern Standard Time, 
JBeer@BooseCasey.com writes:

> Ok, list traffic is light, so maybe someone can help. Patient is a 1991 200q
>  20v, 160k.  IA3(about 2-3 years old), 2Bennett k24/26 hybrid.  When set to
>  16 psi per VDO via some spring shims(car gauge reads 1.8), car pulls
>  cleanly. If I shim the spring to pull 20psi (car gauge 1.9-2.0), car has a
>  flat spot anywhere between 17 and 20 psi.  Hard to describe- feels like a
>  very soft rev limiter. For you "old timers". feels like a stuck needle in a
>  needle and float motorcycle carb setup. If I get go pedal off the floor a
>  little, it clears right up and car surges forward. The boost gauge seems to
>  hold whatever boost level the car is at when this occurs.  Seems a little
>  worse when car gets hot from repeated runs at boost, but it won't occur
>  every time. Most runs are in the higher gears.  Both knock sensors recently
>  replaced, plugs (F5dpor) relatively new.  WOT switch?  Fuel pump not 
>  enough? (not terribly noisy).  Other than this problem, the car flies. No
>  fault codes read out. Any WAGS?  TIA
>  Regards,
>  Jerry

Jerry:  I think you should discuss this with Ned at Intended Acceleration, 
since he's the one that provided your chip.  As I understand the ECU, a 
stiffer wastegate is not needed for higher boost; a little stiffer than stock 
might help wastegate "cracking"; but beyond that and the ECU might fight to 
reduce boost to expected levels.  Try running with a wastegate frequency 
valve test light installed, and see what the ECU is trying to do to the 

As I recall, the ECU doesn't control knock/boost at partial throttle (less 
than say 1/3).  With your stiffer spring, it's allowing full boost and not 
reducing the timing etc., I would think.  The "flat spot" you're feeling 
could be the ECU trying to dial back the boost, then giving up... which would 
be shown by the wgfv test light.

How about installing a pressure gauge on the fuel rail, to see what the fuel 
pressure stays at during higher boost?

Scott Mockry reported a while back about a 200q20v that had bad solder joints 
in the throttle position switch; it can be opened, the joints tested and 
resoldered, and reinstalled (or just replaced).  The switch measures throttle 
position, as well as the speed at which the throttle is depressed.

HTH, chris miller, windham nh, c1j1miller@aol.com
'91 200q20v ==> http://members.aol.com/c1j1miller/index.html