Just as computers have improved , so have Fuel
Injection computers, and now they all have more
features to make troubleshooting easier with
improved driveability .

Self diagnostics. Limp-home modes if major
sensors fail.
More accurate timing with Crankshaft Postion
Sensors, sequential fuel injector operation,
individual spark timing.
Adaptive managment control- optimizes fuel
economy for highway or city driving.

Digifant is obsolete compared with modern VW
systems so there's not much you can do with it.
I wonder why the Vanagon Digifant did'nt at least
get knock sensor control as other VW's did in the
'80's.

Robert

1982 Westfalia 2.0 Motronic

--- Geza Polony <gezapolony@SBCGLOBAL.NET> wrote:

> I've been trying to tune my '84 Westy, and
> reading about others' attempts to
> do the same, for a few months now, and I've
> come up with a question I can't
> answer. It regards the input of the various
> sensors to the ECU and the way
> the ECU determines fuel/air mixture.
>
> Let's say you have two identical, 22 year old
> Vanagons next to each other,
> and you're trying to tune both. The voltage
> from the sensors is going to be
> different for the same conditions, just because
> of age and manufacturing
> variability. So at 950 rpm at 185 degrees F (or
> whatever) the voltage from
> the AFM, the O2 sensor, the Temp II, the intake
> air temp sensor, and so
> forth, are going to be different from van one
> to van two.
>
> There's no way around this, if only because you
> can't get "correct"
> resistance specs for the potentiometer in the
> AFM.
>
> In practise, to set the FI mixture, mechanics
> put a sniffer up the exhaust
> pipe and turn the AFM screw, etc., until the
> readings are within specs.
>
> But this doesn't really tune the engine at all
> temps, RPMs, loads, etc. It
> just sets it for one condition.
>
> The sensors in the two vans are going to be
> putting out different voltages
> for 4150 RPM, 190 degrees F water temp, 85
> degrees F air temp, open
> throttle, etc.  So the ECU will be sending a
> different mixture to the FI's,
> FOR THE SAME CONDITIONS.
>
> This leads me to believe that the ECU is in
> reality a relatively crude
> device, with huge margins for error from the
> sensors. Otherwise, the vans
> just wouldn't run. Or they would run at one set
> of condition, but not at
> another.
>
> This in turn leads to relatively inefficient
> operation, in terms of engine
> output and gas mileage.
>
> The variability of the sensors's output, take
> together, also makes these
> cars exceedingly difficult to tune accurately.
> And this isn't even taking
> into account the ignition!
>
> Am I on track with my thinking here? Is there
> something I'm missing about
> the fuel management system?
>
> Thanks for reading
>
>
> Geza
>

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