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Re: Stuttering


On 21 Nov 2005 at 16:25, Constantino Tobio wrote:

> The voltage coming out of the sensor has shifted downward, also, sending
> a signal to the brain that the sensor is operating at a voltage for a
> different expected temp. We know the head sensor is the main input on
> whether cold  enrichment is necessary. I believe the resistance of the
> head temp sensor is highest the colder it is. If it's getting less
> voltage as input, it will proportionately supply less voltage signal to
> the brain, tricking the brain into thinking it's colder. If the brain
> THINKS its colder than it is, then that would explain how lower than
> expected voltage would make a car run richer than necessary. 

You're right that the head sensor R goes up as the temp goes down. 
Unfortunately, this would mean that the voltage it would deliver to 
the brain (remember, one side of it is grounded, so the brain can 
only see its "high" side) will be the highest when it is cold and 
lowest when hot. That's just the opposite of your theory.

I don't think it's fair to just single out one part of the system and 
say that it's at fault, but I could be wrong about that. It's 
possible that Bosch designed in a "feature" to make things richer 
when starting and the system voltage was pulled down. It's quite 
possible that this was designed in, but it has this unintended 
consequence.

Maybe someday I'll work all the way thru the circuit. We know it's 
really not all that complicated, since we've seen other D-Jet brains 
which have been traced out for other cars. I suspect that they are 
all pretty much alike, with only resistors changed to meet the needs 
of various engines and sensors.

-- 
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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