Ok ... admittedly I'm guessing here but ... maybe the ECU is sending the
signal (because the other half of the brain has cut the fuel off) for
enrichment because it sees a lean condition coming from the O2 sensor
(lean because the fuel is cut off, of course).  In other words, not the
smartest system but, in that the fuel is already cut off the enrichment
signal doesn't really do anything.

Like I said ... just guessing!

Mike

Michael Elliott wrote:
> According to Bentley's and the VW Digijet Protraining manual for the
> 1.9l engine, if the Throttle Idle Position Switch is closed (foot off
> gas) AND if the engine is at more than 1500 rpm, fuel to the engine will
> be cut off.
>
> I know the switch is working and that it is connected to the ECU because
> I have an LED which I can see while driving temporarily wired it. The
> LED goes dark when my size 10 is off the pedal, indicating that the
> switch is shorting ECU pin 4 to ground, and since that voltage comes
> from the ECU, the ECU "sees" the switch.
>
> I know the ECU is seeing engine rpms because it would just shut off fuel
> if it didn't think the engine was running.
>
> So it appears that the ECU is getting all the input it needs: throttle
> idle position switch and rpm.
>
> But when going downhill in gear, foot off gas as indicated by dark LED,
> and with the transmission revving the engine above 1500 rpm, the O2
> sensor goes full off-scale rich.
>
> The O2 sensor is new, and I'm monitoring it on my Ken Lewis-0-Matic O2
> meter. During normal driving and idling, it bounces around in quite a
> lively fashion.
>
> Based on this, it appears that the engine is NOT cutting off fuel as the
> manual says, and I am puzzled. I've tried a second ECU with the same
> result. What, oh what, could I be overlooking?
>
> --
> Mike "Rocket J Squirrel" Elliott
> 71 Type 2: the Wonderbus
> 84 Westfalia: Mellow Yellow ("The Electrical Banana")
> 74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
> KG6RCR
>