[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index] 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 pumps. 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 -- /// Ti Kan vorsprung durch technik /// AMB Research Laboratories, Sunnyvale, CA. USA /// Internet: ti@amb.org ////// UUCP: ...!uunet!bazooka!ti ///
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