cold start problems (frequency valve?)

[Mike_Buckham at ptk.pioneer.co.uk]

Older UK spec cars do not have O2 sensors to perform fine calibration of
the fuel mixture. Mine is a 1989 200qta with a MAC-12D ECU. There is no O2
sensor and the O2 sensor inputs to the ECU are disconnected (where they
would usually be connected on a MAC11 ECU). So I was wondering... why do
these cars still have a frequency valve to adjust the fuel pressure? What
is the ECU using to change the duty cycle on this valve, as there doesn't
seem to be any input which it could use to make any adjustments?

I think my engine is running too lean at the moment, which is causing it to
knock and the ECU keeps retarding the ignition. I am experimenting with the
mixture by slightly increasing it now and again and the ECU certainly seems
to be retarding the ignition less and less. Soon I will be able to achieve
nearly full throttle (without the full throttle switch closing) without any
loss of power.

Cheers, Mike.

===============================================================================

Message: 2
From: Ti Kan <ti at amb.org>
Subject: Re: cold start problems
To: bwpearre at alumni.princeton.edu
Date: Wed, 4 Jun 2003 22:53:53 -0700 (PDT)
Cc: digitizit at msn.com (Digitalorg), quattro at audifans.com

...

For the home mechanic, one can get reasonably good results by measuring
the output voltage of the O2 sensor while making the adjustment (again,
the O2 sensor has to be disconnected).  A good voltmeter meter with
high input impedance should be used for this, so that the meter itself
does not load down the O2 sensor output and affect the reading.
A target of about 0.8V to 1V is usually good.  Then, when the O2 sensor
is reconnected, the closed loop feedback system will dynamically optimize
the actual mixture.

...

-Ti
2003 A4 1.8T multitronic
2001 S4 biturbo 6-sp
1984 5000S turbo
1980 4000 2.0 5-sp


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