On 8/17/2009 2:01 PM mark drillock wrote:

> Yes, that is it, the ECU knows by the hall pulses how fast the engine is
> turning. When it sees the idle switch closed but rpms high it knows you
> are coasting in gear and cuts off the injectors.
>
> If you have one of the Ken Lewis O2 meters installed you can see this
> happen in real time.

You sure can. The meter slams over to the left (left = lean, right = rich)
the moment the ol' toe lifts off the pedal.

During the long descents I've described, the meter stays locked in the
lean/no-fuel condition the whole time.

--
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
Bend, OR
KG6RCR
>
> This is part of why a sticking or badly adjusted idle switch can make
> the van herky-jerky to drive.
>
> Mark
>
> pdooley wrote:
>> Hmmm, I may have an answer for my own question.
>> The hall sender could detect RPM below or approaching idle speed and add
>> fuel.
>>
>>
>> -----Original Message-----
>> From: pdooley [mailto:psdooley@verizon.net]
>> Sent: Monday, August 17, 2009 4:45 PM
>> To: 'Rocket J Squirrel'; 'vanagon@GERRY.VANAGON.COM'
>> Subject: RE: Not quite a backfire . . .
>>
>> How does this work?
>> How does the ECU know to shut fuel completely off when descending but yet
>> could add fuel in a split second to prevent stalling if say, you press
>> the
>> clutch pedal in?
>> The idle switch cannot discern the difference between idling and
>> coasting in
>> gear.
>> I really don't see how the AFM could perform this function either.
>> Somebody enlighten me.
>>
>>
>> <With no pressure on the gas pedal, the fuel is totally shut off, so the
>> engine is not firing on any cylinders.....
>>
>