GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual

Gasoline Fuel Filter

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The fuel filter should be serviced every 15,000 miles on most carbureted vehicles, while most fuel injected vehicles have a suggested interval of 30,000 miles. If the truck is operated under severe conditions, change it more often. Three types of fuel filters are used, an internal pleated-paper element type (located in the carburetor fuel fitting), an inline filter (located in the fuel feed line) and an in-tank type (the "sock'' on the fuel pickup tube).

If an inline fuel filter is used on an engine which has a filter installed in the carburetor body, be sure to change both at the same time.


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 before it is disconnected in order to catch any remaining fuel which may escape.

Throttle Body Injection (TBI)
TBI MODEL 300 or 700 (2.5L ENGINE)
  1. Place the transmission selector in PARK (automatic transmissions) or NEUTRAL (manual transmissions), then set the parking brake and block the drive wheels.
  2.  
  3. Loosen the fuel filler cap to relieve tank pressure.
  4.  
  5. Either remove the FUEL PUMP fuse from the fuse block in the passenger compartment (early model vehicles) or disengage the three terminal electrical connector at the fuel tank (late model vehicles). If you are unsure which method works for your truck, try removing the fuel pump fuse. If this does not disable the pump, the electrical connectors at the fuel tank must be disengaged.
  6.  
  7. Start the engine and allow to run until it stops due to lack of fuel.
  8.  
  9. Engage the starter (turn key to START ) for three seconds to dissipate all pressure in the fuel lines.
  10.  
  11. Turn the ignition OFF , then re-engage the connector at the fuel tank or install the fuel pump fuse.
  12.  
  13. Disconnect the negative battery cable to prevent accidental fuel spillage should the ignition key accidentally be turned ON with a fuel fitting disconnected.
  14.  
  15. When fuel service is finished, tighten the fuel filler cap and connect the negative battery cable.
  16.  

TBI MODEL 220 (2.8L AND 4.3L ENGINES)
  1. Disconnect the negative battery cable.
  2.  
  3. Loosen fuel filler cap to relieve fuel tank pressure.
  4.  
  5. The internal constant bleed feature of the Model 220 TBI unit relieves fuel pump system pressure when the engine is turned OFF . Therefore, no further action is required.
  6.  
  7. When fuel service is finished, tighten the fuel filler cap and connect the negative battery cable.
  8.  


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

Multi-Port Fuel Injection (MFI)/Central Multi-Port Fuel Injection (CMFI)

A schrader valve is provided on components of these fuel systems in order to conveniently test or release the fuel system pressure. A fuel pressure gauge and adapter will be necessary to connect to the fitting. The MFI system covered by this manual uses a pressure fitting located on the fuel rail assembly or at the fuel inlet pipe junction. The CMFI system covered here uses a valve located on the inlet pipe fitting, immediately before it enters the CMFI assembly (towards the rear of the engine).

  1. Disconnect the negative battery cable to assure the prevention of fuel spillage if the ignition switch is accidentally turned ON while a fitting is still disconnected.
  2.  
  3. Loosen the fuel filter cap to release the fuel tank pressure.
  4.  
  5. Make sure the release valve on the fuel gauge is closed, then connect the fuel gauge to the pressure fitting located on the fuel rail, pipe or fitting, as applicable.
  6.  
  7. Install the bleed hose portion of the fuel gauge assembly into an approved container, then open the gauge release valve and bleed the fuel pressure from the system.
  8.  
  9. When the gauge is removed, be sure to open the bleed valve and drain all fuel from the gauge assembly.
  10.  

REMOVAL & INSTALLATION




CAUTION
Filter replacement should not be attempted when the engine is HOT. Additionally, it is a good idea to place some absorbent rags under the fuel fittings to absorb any gasoline which will spill out when the lines are loosened.

Internal Filter

See Figures 1, 2 and 3

The carburetor inlet fuel filter should be replaced every 15,000 miles, or more often if necessary.

  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. Torque the filter nut-to-carburetor fitting to 25 ft. lbs. (34 Nm).
  4.  

When working on fuel line fittings, take care not to overtighten the fittings. A crow's foot will be necessary to use the torque wrench to tighten fuel fittings.

  1. Connect the fuel line to the filter inlet nut and tighten the fuel line to 18 ft. lbs. (24 Nm). Be sure to use a backup wrench to prevent the filter nut from tightening.
  2.  
  3. Start the engine and check for leaks.
  4.  



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Fig. Fig. 1: If necessary, disengage any wiring which is in the way of the fuel inlet filter nut



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Fig. Fig. 2: Once the fuel line is disconnected, the filter nut may be unthreaded from the carburetor



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Fig. Fig. 3: Remove the filter and spring from the nut

Inline Filter

See Figures 4, 5 and 6

To locate the inline filter, follow the fuel line back from the carburetor or throttle body. Inline 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.


CAUTION
Before disconnecting any component of the fuel system, refer to thefuel pressure release proceduresfound earlier in this section.

  1. Properly relieve the fuel system pressure.
  2.  

Some late model vehicles are equipped with "quick-connect'' fittings. A special tool must be used to release the locking tangs on these fittings.

  1. Using a backup wrench (on threaded fittings) 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.
  2.  
  3. Remove the fuel filter from the retainer or mounting bolt. For most filters which are retained by band clamps, loosen the fastener(s) and remove the filter. For some filters it may be necessary to completely remove the clamp and filter assembly.
  4.  

To install:
  1. Position the filter and retaining bracket with the directional arrow facing away from the fuel tank, towards to 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, the with arrow facing away from the fuel tank.

  1. Install and tighten the filter/bracket retainer(s), as applicable.
  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 and tighten the fuel filler cap, then start the engine and check for leaks.
  6.  



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Fig. Fig. 4: Inline fuel filter-2.5L engine



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Fig. Fig. 5: Inline fuel filter-2.8L engine



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Fig. Fig. 6: Inline fuel filter-4.3L engine

In-Tank Filter

See Figure 7

To service the in-tank fuel filter,please refer to the electric fuel pump procedures found in Chapter 5 of this manual.



Click image to see an enlarged view

Fig. Fig. 7: Common in-tank electric fuel pump and filter assembly-fuel injected engines

 
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