Date:         Sun, 30 Dec 2001 19:52:52 -0600
Reply-To:     Larry Alofs <lalofs@ENTERACT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Larry Alofs <lalofs@ENTERACT.COM>
Subject:      Re: Understanding AFC fuel injection--question
Comments: To: Adam Puzerewski <VGONMAN@MSN.COM>
Content-Type: text/plain; charset=us-ascii

Adam Puzerewski wrote:
>
> Volks,
> I just spent the better part of the day diagnosing my fuel injection on my 81 and am back where i started.
>
> I have an official vw AFC book, as well.  What I do not get is the process when it is starting cold.....air flows thru the AFM, and if the motor is cold enough, the auxillary air regulator is open, and air is diverted to the intake manifold, thus bypassing the throttle body.  This book says that this enables the motor to act the same cold as it does hot, for the control unit adds additional fuel to the injectors when it senses the engine is cold.  Now, there is no sensor, or anything on the throttle body, so how does this auxillary air regulator do anything?  The air still ends up in the intake manifold and thus diverted to the cylinders anyway..................I could see it doing something if it were unregulated air, but it is regulated at the AFm.................
>

The air that goes thru the aux air regulator when the engine is cold has
been measured at the AFM, so the ECU knows that this air is going to the
manifold and adjusts the fuel pulse duration accordingly.  The mixture
is also enriched based on temperature sensor info.  It is better to say
that the AFM meters (measures) the air flow rather than regulates it.
  To keep a cold engine running you could perhaps hold the throttle open
slightly with the gas pedal.  The aux air regulator does it for you.
  The choke on an old fashioned carburetor enriched the mixture while
cold, but also held the throttle open slightly.

Larry A.