Re: UrQ Bad Bad Idle

[Robert Houk - WorkGroup Server Firmware <Robert.Houk@East.Sun.COM>]

   I decided to try and solve my strange 1983 UrQ idle problem this weekend, 
   while poking around with my new JC Whitney fuel pressure gauge for CIS. Here's 
   what I found, and please let me know if there is anything abnormal. 

   My Cold Control pressure is perfect, so is the hot control pressure.
   My system pressure is 90 psi. Doesn't this seem high?

Seems 'bout right...

						       When I turn the gauge to 
   read system pressure (i.e. closed, no pressure regulator return) the car runs 
   really poorly and almost stalls.
   As soon as the car goes open loop the rough idle starts and will stall the car 
   unless revved. Hot idle is perfect,
   The rough idle will also happen upon hot start-up. When hot the duty cycle 
   goes straight to a constant 50%. Then after 1 min it goes to constant 90%, 
   then back to constant 50%, then to constant 90%, then it goes into open loop 

"Open Loop" is "static" mappings, as in when you first turn the car on
and it's not up to temp yet (either of "cold block" [below roughly
94F] or O2 sensor not yet operational); "closed loop" is the con-
stantly-fluctuating duty cycle as the ECU is constantly adjusting the
mixture (via the frequency valve) based on the O2 sensor voltage
(trying to maintain 0.5V). I presume you mean "closed loop" here...

   about 65% with fluctuation.  The bad idle occurs at the constant 50%. It idles 
   very well at the 90% stages. Anyone have a thoughts?

Ideally, the ECU should be maintaining 50% duty cycle -- or, more
properly, the rest of the system should be such that the ECU zeroes in
on 50% as the appropriate duty cycle; lower duty cycle means the
system is running rich and the ECU is leaning out the mixture, while
higher duty cycles indicate the system is running lean and the ECU is
enrichening the mixture.

Running around 65% means your static/idle mixture is pretty lean.

What *I* do with *my* UrQ is to adjust the static idle mixture (adjust
in the fuel distributor) for a duty cycle in the 42-50% range (i.e.,
the static mixture is slightly rich. This way, when "cold" (i.e.,
running open loop) the mixture is slightly rich, and the engine is
happier. (I also find that I need to adjust twice a year, for both
"winter" and "summer" environments.) Make sure the car is completely
warmed up (oil et al) and stable before making these adjustments.
(Parenthetically, I will also add I both richened the open loop
mixture and extended the open loop temp threshold [to about 130-140F]
for my Schrick cam, which definitely likes a richer mixture than the
stock cam.)

I also target 950-1000rpm as the no-load idle speed (I also adjusted
the ECU idle map correspondingly to raise the idle thresholds, as 
described in my WEB site).

This gives me a slightly fast but smooth, dependable and happy idle,
dropping to no lower than the high-700's under worst case load (by
"load" I mean electrical, rad fan on hurricane force, high beams,
fan on full, rear defroster, rolling windows up and down).

My many-$'s worth.

					-RDH

P.S.	I am at a complete loss to explain the open-loop 90% readings.
	That is very strange, I've never seen that one with *my*
	beastie.