[urq] hesitation at higher RPM & boost

Ben Swann benswann at comcast.net
Wed Jul 26 10:11:32 EDT 2006

'83 Ur Quattro  - new injectors, vac lines, ignition, fuel pump, filters and
fairly well sorted over and over.  The car passed emissions with flying colors
- CO reading 1/10 of allowable standard and 0% HC which is amazing.  The car
still has a little bit of a hard start problem particularly when warm after
sitting, and usually starts right up when cool.


After installing the JCW  air/fuel ratio guage, I note good mixture and
operation during normal acceleration and cruising.  Still there is this
strange hesitation at full accel - over 4000 RPM usually and boost at/over 1.8
bar.  The air fuel ratio guage indicates more of a rich condition than the
lean condition I expected at full throttle - this tells me there should be
more power on tap, or am I running out of air?  If there is any air leak under
boost, I don't know where it could be.  The guage hits one light below max
rich usually.


I have the fuel pump jumpered on with ignition, so no fuel cutout.  I have a
means to enrich or enlean CPR if need be, but does not seem to make any
difference, except that I had boost controlling the CPR to enrich which is now
undone.  Still AF on rich side at full throttle.


I notice that if backing off of full throttle a little, there is somewhat of a
momentary power surge.  I set the full throttle switch cut-on a little higher
and seemed to help, but not much, except what I perceive was XS rich was less
pronounced.  Should I be in the 12:1 fuel air range at full throttle?


I installed a Jacobs ignition which definitely helped, but still seems to be a
bit of hesitation - like there is more power on tap, but maybe ignition is
being retarded. I fell the power coming on then dropping out - inconsistent.
Sometimes she feels like it has a 1.8 bar MC engine and other times the power
just isn't there.  The power increase I noticed after adding the Jacobs
ignition boost was dramatic when  relatively cold, but after warmup, seems to
drop off, although still better than before I added the ignition booster.


After having been over this engine over and over, I'm wondering what else it
can be.  The problem is minor, but enough that it will effect acceleration in
autocrossing situation or passing. 


Oh I also installed a Bypass valve which helps smooth out shifts, but made no
difference with this "problem".


Is this a timing retard due to the intake air sensor indicating to hot intake
air temp?  and if so, how do I override or compensate?  - short of adding a
larger intercooler, etc.




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