[urq] hesitation at higher RPM & boost

[Ben Swann]

See *** comments&questions ***

From: tlum at flash.net [mailto:tlum at flash.net] 
Sent: Wednesday, July 26, 2006 12:57 PM
To: benswann at comcast.net
Subject: Re: [urq] hesitation at higher RPM & boost

Boost up to around 2 Bar - I can do more, but silly until I get this resolved.
++++++++++++++++++++++++++++++++
I'm assuming 1 bar over normal 1 bar atmo or 14.5 PSI boost right?
***CORRECT***
++++++++++++++++++++++++++++++++

F/TCU has a TAP chip - don't know much about it, just happened upon the ECU
one day.
++++++++++++++++++++++++++++++++
I have the same chip in my MAC02.  I dyno'd it on the ATP Turbo 4wd dyno at
152WHP, 13.3 AF at 15 psi indicated on my VDO boost gauge with no seeming
stumble.  To be a bit more conservative, I adjusted the WG to limit boost to
12 psi.
*** I would doubt I have overboost problems.  The compression ratio is so low,
I normally run on 87 octane. I plan to install a Schrapnel Knob  and possibly
P.T, resistor to purposely advance timing - already cranked on the WG - that
got the 2 bar ***
++++++++++++++++++++++++++++++++

Injector cooling fan works, but I should probably put in a switch or after-run
system, as it only kick on when extremely hot.
++++++++++++++++++++++++++++++++
I changed my switch to run at 85C instead of 95C to run fan almost after every
run.
*** OK - good idea.  Where do you get this switch? ***
++++++++++++++++++++++++++++++++


I doubt I get any CS inj. For hot start - been tempted to put in a manual
trigger.  Sometimes I need to introduce fuel when having hot start issue.  I
did not have the problem with the CPR mod - enriches based on airflow - using
venturi effect from port at turbocharger - works a little too well, but
indicates there is enough fuel to be had if need be.
++++++++++++++++++++++++++++++++
Hot starts are sometimes a little tricky after say 20 minutes and I have to
listen carefully to hear the engine catch.
++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++
I'm going to switch to 034efi and a MC2 engine soon.  Nothing wrong with the
WX except for a marshmellowy takeoff even with a K24 turbo making boost at
1900 rpm.  Jeff Lewis's MC1 034efi starts in under 2 revs and has tremendous
power and yet excellent fuel economy. ++++++++++++++++++++++++++++++++
*** I plan to keep this one nearly stock as everything CIS has been reworked
or new - it runs to good to replace, but I'd like to get it perfect.  I have
at least three other engines to do EFI - 034 or MS on and two are going into
UrQ's.  ***

++++++++++++++++++++++++++++++++I'd double check the intake temp sensor leads.
That sensor is so low resistance, anything marginal might cause the timing to
back off. ++++++++++++++++++++++++++++++++
*** BTDT several times - even replaced the temp sensor ***

Have fun,  *** I plan to!  BEN ***

Tony

-----Original Message-----
From: tlum at flash.net [mailto:tlum at flash.net] 
Sent: Wednesday, July 26, 2006 10:23 AM
To: benswann at comcast.net
Subject: Re: [urq] hesitation at higher RPM & boost

Ben, how much boost are you running?  Is your F/TCU chipped?  Make sure your
injector cooling fan is working.  Hot starts can be a little problematic, but
not severe.  Supposedly there's a hot start relay involving a pulsing cold
start valve, but my car doesn't have it.

Tony
'83 urquattro #302

= = = Original message = = =

'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.

Ben