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200T Head Gasflow?
In message <199801141255.HAA24015@camel14.mindspring.com> firstname.lastname@example.org (Jeffrey J. Goggin) writes:
> >John Robinson has gasflowed his MB engine and finds that performance has
> >_suffered_ as a result. If you put more air in, ya gotta put more fuel in to
> >keep the mixture right. That's basically controlled by the air mass sensor
> >to a point) and then by the ECU. How do you tell the ECU that more air is
> >going in for a given boost level? The ECU is not connected to the air mass
> On CIS-equipped cars, the fuel-to-air ratio is self-adjusting, up to a point
> ... in my experience, most Audis respond well to mild porting work (really
> nothing more than cleaning up casting flash, match-porting gaskets, etc.)
> without making ANY changes to the fuel system. If the head is apart anyway,
> it's kinda silly NOT to do this as the only downside is paying someone to do
> it if you're not capable of doing it yourself...
I think it's the 'up to a point' that's the issue at present. Scott
Mockry and I have been playing around with air mass sensor potentiometer
readings that tend to show air plate deflection ceases to be a useful
input at the normal design max bhp point of these engines. From there
on, you're flying blind on ECU maps driving the fuel frequency valve.
One interesting 'blip' - it seems impossible to use max/min meters,
because to do the test you have to drive the system into the fuel
pump cut-off logic. At the point where the fuel pump cuts, system
and control pressures cease to exist - the sudden lack of control
pressure counteracting the air mass sensor's displacement seems to
fling the paddle to the farthest point of its travel.
Another major surprise - though it may be coincidence - is that the
two MB engines so far measured have air mass sensor potentiometer
outputs that are _identical_ within the accuracy of the DVM I've been
using. Did Audi calibrate this device - and if so, what the &$@# for?
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