GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Gasoline Fuel Filter

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There are three types of fuel filters; internal (in the carburetor fitting), in-line (in the fuel line), and in-tank (the sock on the fuel pickup tube).


CAUTION
Before removing any fuel system component, always relieve pressure from the system.

FUEL PRESSURE RELEASE



Carbureted

To release the fuel pressure on the carbureted system, remove the fuel filler cap from the fuel tank in order to allow the expanded vapor to escape, then reinstall the cap. A rag should be placed around a fuel fitting to catch any remaining fuel which may escape.

Throttle Body Injection (TBI)

When servicing TBI vehicles, the fuel filler cap should be removed in order to relieve tank pressure, then reinstalled. The TBI unit used on these engines contains a constant bleed feature in the pressure regulator that relieves pressure any time the engine is off. Therefore, no special relief procedure is required. However, a small amount of fuel may be released when the fuel line is disconnected.


CAUTION
To reduce the chance of personal injury, cover the fuel line with cloth to collect escaping fuel and then place the cloth in an approved container.

REMOVAL & INSTALLATION



Internal Filter

The carburetor inlet fuel filter should be replaced every year or 15,000 miles or more often if necessary. This paper element filter is located behind the large fuel line inlet nut on the carburetor. Some vehicles may also have an in-line fuel filter located between the fuel pump and carburetor. This filter should be changed at the same time as the inlet-type filter; in both cases filters should only be changed when the engine is cold for safety related reasons.

  1. Disconnect the fuel line connection at the fuel inlet filter nut on the carburetor. A backup wrench should be used to prevent the fuel filter nut from loosening while trying to remove the line.
  2.  
  3. Carefully loosen and remove the fuel inlet filter nut from the carburetor.
  4.  
  5. Remove the filter and spring.
  6.  

To install:

If a check valve is not present with the filter, one must be installed when the filter is replaced. The check valve is necessary in order to meet Motor Vehicle Safety Standards (MVSS) for roll-over.

  1. Install the spring, filter and check valve making sure the valve end of the filter is facing the fuel line. Ribs on the fuel filter will prevent it from being installed incorrectly, unless it is forced into position.
  2.  
  3. Connect the fuel line to the filter inlet nut.
  4.  
  5. Start the engine and check for leaks.
  6.  

In-line Filter

See Figure 1

To locate the in-line filter, follow the fuel line back from the carburetor or throttle body. In-line filters are often mounted to the frame rail underneath the vehicle. It may be necessary to raise and safely support the vehicle using jackstands in order to access the filter.

  1. Disconnect the negative battery cable to prevent fuel spillage if the ignition is accidentally turned ON.
  2.  
  3. Using a backup wrench to prevent overtorquing the lines or fittings, loosen, and disconnect the fuel lines from the filter. Be sure to position a rag in order to catch any remaining fuel which may escape when the fittings are loosened.
  4.  
  5. Loosen the retaining bolt, then remove the retaining bracket and/or fuel filter from the vehicle.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: In-line fuel filter mounting.

To install:
  1. Position the filter and retaining bracket with the directional arrow facing away from the fuel tank, towards the carburetor or throttle body.
  2.  

The filter has an arrow (fuel flow direction) on the side of the case, be sure to install it correctly in the system, with the arrow facing away from the fuel tank.

  1. Install and tighten the filter/bracket retainer.
  2.  
  3. Connect the fuel lines to the filter and tighten using a backup wrench to prevent damage.
  4.  
  5. Connect the negative battery cable, then start the engine and check for leaks.
  6.  

In-Tank Filter

To service the in-tank fuel filter, please refer to the electric fuel pump removal and installation procedure in Fuel System of this information guide.

 
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