Monday, Oct 11, 2004 at 22:05
--------------------------------------------------------------------------------------------- Here`s a post i have lifted from another site some interesting facts
Maurie
The 4.2 TDI (current model) has the same pump as the old one, the
only difference is an electronic timing control.
One of the most polluting gases emmitted by diesels is Oxides of
Nitrogen (not visible) and particulate matter (grey/black smoke).
To pass pollution control the 4.2TD (previous version) had the timing
retarded slightly to reduce Oxides of Nitrogen.
The new one has a sensor on injector number one (you will notice the
injector is different) from where it receives a knock reading and the
control unit retards/advances the timing accordingly, however the
pump still has the mechanical centrifugal advance, it is just the
initial timing which is controlled.
Everything else is the same, it also has an idle posistion sensor to
tell the system when you have taken the foot off the throttle so it
can retard the injection right off and to turn on/off the EGR (which
is also to reduce Oxides of Nitrogen).
The turbo housing is small on purpose, it allows the turbine to spool
at low RPM for better driveability and no turbo lag, however the side
effect is less high RPM power.
By changing the housing/turbine they change the flow and it gains
power at higher RPM but looses some of the low end torque.
Depending what you are after the modification may be a solution for
you, if you are after highway power go for it, if you are on the
other hand after off road torque and flexibility, leave it as it is.
All other changes as advertised by certain people are a compromise
not worth the effort, most of them bypass the turbo wastegate
(causing it to overboost), fiddle with the aneroid settings, (in the
older ones they also advanced injection timing) with disregard for
Oxides of nitrogen which are harmfull for the environment and also
for the engine.
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