Re: 88 MB Urq questions

["Lino M. Valadas" <valadasl@osha.igs.net>]

>> > As for the US MC engine, it forgets about the O2 sensor pretty much
>> > as soon as you go on boost and uses one of two RPM based duty cycle
tables
>> > for the frequency valve... (one table for low boost, one for
>> > not so low boost levels).  There is no carry forword of anything learnt
>> > by the O2 sensor to on-boost behavior.
>
>> As you showed, the MAC12D is a cut-down MAC11.  I would not expect any
>> carry-forward here.
>
>I just remembered something else that may be of interest.  The MAC11 uses
>a base duty cycle of 50% for controlling the mixture via the O2 sensor.
>The MAC14 (some 89 MC engines and later) has an RPM/MAP based table
>of base duty cycles!  So, the fuel metering needs compensation to
>try to maintain a given A/F ratio.
>
Snip........

I have been following this thread with interest, and I would like to put
some questions up for grabs regarding my Ur-Q.
The previous owner appears to have replaced the engine with a MC, and
definitely installed a MAC11b on my 83 Ur-Q.
My car has a problem similar to the one reported by Phil on John's car.  In
my case it accelerates rapidly until it gets to about 4500-5000 RPM and then
sits there surging taking forever to get to 6000 RPM.
The MAC11 seems to be controlling some functions like timing, but how can it
control the fuel management if there is no duty cycle frequency valve.
I'm thinking of installing one and observe the results any thoughts.
There is a solenoid valve controlling vacuum at the warm-up valve,  I can't
get any info on this system on Bentley's nor Haynes.  It turns vacuum on at
the warm-up valve when the ignition is on, but that all I know.  Does
anybody have more info on its function?  Any information would be
appreciated.

TIA

Lino
86 5ktqw
83 Ur_Q