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Re: Fuel filter intervals on Audi 4000

Phil Payne writes:
> In message <Pine.SUN.3.91.950102103941.271A-100000@crl8.crl.com> Edward Armstrong writes:
> > 
> > .......The filter is composed of pleated paper tightly wound up
> > like toilite paper.
> Now you're confusing me.  European VW/Audi 5 cylinder carburettor engines have 
> small petrol filters (1 1/2" long, 3/4" in diameter) in the petrol line in the 
> engine bay, quite near the camshaft-driven mechanical petrol pump.  The hoses 
> are just push-fits on the ends of the filter housing.
> Is this the same beast?

No.  Cars with Bosch CIS (K-Jetronic) or CIS-E (KE-Jetronic) fuel
injection have a much larger fuel filter.  It has a metal body,
about 6 inches long and 3 inches in diameter.  It offers much better
filtration performance than the carburetor fuel filters, because
the fuel distributor and injectors have very fine passages that
do not tolerate much dirt.  These filters are connected to metal
fuel lines on both ends via banjo bolts and copper washers due to
the higher pressure.

The Bosch Motronic and VW Digifant systems found in recent
VW/Audis (pulsed, rather than continuous injection) also have
similarly large filters.

Fuel injected VW/Audis also do not have mechanically-driven fuel pumps.
They have an electric pump that produces a much higher fuel pressure
that is required by the fuel system.  Some cars even have two fuel

U.S. VWs and Audis have all been fuel injected since the late 70s.

Some Audis actually have two fuel filters (particularly the 4000/Coupe
series).  One of these is near the outlet of the fuel tank just
upstream of the fuel pump.  This is a plastic unit not unlike those
found on the carburetor cars and is really a pre-filter to prevent
really big particles from entering the fuel pump.  The other filter
is the aforementioned metal one, sometimes located under the car near
the fuel pump as well, or under the hood on the firewall or shock tower.
This unit is upstream of the fuel distributor.

The small platic filter costs only a few dollars, but the big
metal one usually costs more than $20.

Neither of these filters are intended to be lifetime items, although
the replacement interval largely depends on the quality of fuel
used.  They can run for years without need for replacement, but
a really bad tank of fuel can clog them in no time at all.

    ///  Ti Kan                vorsprung durch technik
   ///   AMB Research Laboratories, Sunnyvale, CA. USA
  ///    Internet: ti@amb.org
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