GM Firebird 1982-1992 Repair Guide

Throttle Body

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REMOVAL & INSTALLATION



See Figures 1 and 2

  1. Relieve the fuel system pressure.
  2.  
  3. Disconnect the THERMAC hose from the engine fitting and remove the air cleaner.
  4.  
  5. Detach the electrical connectors at the idle air control, throttle position sensor, and the injector.
  6.  
  7. Disconnect the throttle linkage, return spring, and cruise control (if equipped).
  8.  
  9. Disconnect the throttle body vacuum hoses, fuel supply and fuel return lines.
  10.  
  11. Disconnect the 3 bolts securing the throttle body and remove the throttle body.
  12.  
  13. To install, reverse the removal procedures. Replace the manifold gasket and O-rings.
  14.  
  15. Perform the minimum idle speed adjustment, if necessary.
  16.  



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Fig. Fig. 1: Single injector TBI unit



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Fig. Fig. 2: Dual injector TBI unit

INJECTOR REPLACEMENT



See Figures 3, 4 and 5

Use care in removing injectors to prevent damage to the electrical connector pins on top of the injector, the fuel injector fuel filter and nozzle. The fuel injector is serviced as a complete assembly only and should never be immersed in any type of cleaner.

Single Injector Units
  1. Relieve the fuel system pressure.
  2.  
  3. Remove the air cleaner.
  4.  
  5. Detach the injector connector by squeezing the two tabs together and pulling straight up.
  6.  
  7. Remove the screws securing the fuel meter cover. Note the location of any short screws for correct placement during reassembly.
  8.  


CAUTION
DO NOT remove the four screws securing the pressure regulator to the fuel meter cover. The fuel pressure regulator includes a large spring under heavy tension which could cause personal injury if released.

  1. With the old fuel meter gasket in place to prevent damage to the casting, use a prytool and fulcrum to pry the injector carefully until it is free from the fuel meter body.
  2.  
  3. Remove the injector.
  4.  
  5. Remove the large O-ring and steel back-up washer at the top of the injector cavity in the fuel meter body.
  6.  
  7. Remove the small O-ring located at the bottom of the injector cavity.
  8.  

To Install:
  1. Lubricate the new, small O-ring with automatic transmission fluid; then, push the new O-ring on the nozzle end of the injector up against the injector fuel filter.
  2.  
  3. Install the steel backup washer in the recess of the fuel meter body. Lubricate the new large O-ring with automatic transmission fluid, then install the O-ring directly above the backup washer, pressing the O-ring down into the cavity recess. The O-ring is properly installed when it is flush with the casting surface.
  4.  


WARNING
Do not attempt to reverse this procedure and install the backup washer and O-ring after the injector is located in the cavity. To do so will prevent proper seating of the O-ring in the cavity recess which could result in a fuel leak and possible fire.

  1. Install the injector by using a pushing/twisting motion to center the nozzle O-ring in the bottom of the injector cavity and aligning the raised lug on the injector base with the notch cast into the fuel meter body. Push down on the injector making sure it is fully seated in the cavity. Injector installation is correct when the lug is seated in the notch and the electrical terminals are parallel to the throttle shaft.
  2.  
  3. Using new gaskets on the fuel meter cover and a new dust seal, install the cover to the fuel meter body. The two short screws are located adjacent to the injector.
  4.  
  5. Connect the injector electrical connector by pushing straight down until seated firmly in place.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. With the engine OFF and the ignition ON, check for fuel leaks.
  10.  
  11. Install the air cleaner.
  12.  



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Fig. Fig. 3: Removing the fuel injectors



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Fig. Fig. 4: Fuel injector components



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Fig. Fig. 5: Installing the fuel injectors

Dual Injector Units
  1. Relieve the fuel system pressure.
  2.  
  3. Remove the air cleaner.
  4.  
  5. Disconnect the injector connector by squeezing the two tabs together and pulling straight up.
  6.  
  7. Remove the screws securing the fuel meter cover.
  8.  


CAUTION
DO NOT remove the four screws securing the pressure regulator to the fuel meter cover. The fuel pressure regulator includes a large spring under heavy tension which could cause personal injury if released.

  1. With the old fuel meter gasket in place to prevent damage to the casting, use a suitable prytool and fulcrum to pry the injector carefully until it is free from the fuel meter body.
  2.  
  3. Remove the injector.
  4.  
  5. Remove the small O-ring from the nozzle end of the injector and discard it.
  6.  
  7. Remove the old fuel meter cover gasket and discard it.
  8.  
  9. Remove the upper O-ring and steel backup washer from the top of the injector cavity. Discard the O-ring.
  10.  

To install:
  1. Install the steel backup washer in the counterbore of the fuel meter body.
  2.  
  3. Lubricate the new large O-ring with clean engine oil and install it directly over the backup washer. Be sure the O-ring is seated properly and is flush with the top of the fuel meter body surface.
  4.  
  5. Lubricate the new small O-ring with clean engine oil and install it on the nozzle end of the injector. Push the O-ring on far enough to contact the filter.
  6.  


WARNING
Do not attempt to reverse this procedure and install the backup washer and O-ring after the injector is located in the cavity. To do so will prevent proper seating of the O-ring in the cavity recess which could result in a fuel leak and possible fire.

  1. Install the injector by aligning the raised lug on the injector base with the notch cast into the fuel meter body. Push down on the injector making sure it is fully seated in the cavity. Injector installation is correct when the lug is seated in the notch and the electrical terminals are parallel to the throttle shaft.
  2.  
  3. Using new gaskets on the fuel meter cover and a new dust seal, install the cover to the fuel meter body. Use an appropriate thread locking compound on the cover attaching screws.
  4.  
  5. Connect the injector electrical connector by pushing straight down until seated firmly in place.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. With the engine OFF and the ignition ON, check for fuel leaks.
  10.  
  11. Install the air cleaner.
  12.  

ADJUSTMENTS



See Figures 6 and 7

Minimum Idle Speed

Minimum idle speed should only be adjusted when installing a replacement throttle body. The idle stop screw is used to regulate the minimum idle speed of the engine. The throttle body is adjusted at the factory, then covered with a cap or plug to discourage unnecessary readjustment.

2.5L ENGINES
  1. Remove the air cleaner and plug the THERMAC vacuum port.
  2.  
  3. Disconnect the TV cable from the throttle control bracket to allow access to the idle adjustment screw.
  4.  
  5. Remove the throttle stop screw plug or cap.
  6.  
  7. Connect a tachometer to the engine.
  8.  
  9. Disconnect the Idle Air Control (IAC) valve connector.
  10.  
  11. Start the engine with the transmission in PARK (auto transmission) or NEUTRAL (manual transmission) and allow the engine speed to stabilize. All accessories (A/C, rear defogger, etc.) should be OFF.
  12.  
  13. Install tool J-33047 in the idle air passage of the throttle body. Be certain that the tool seats fully in the passage and no air leaks exist.
  14.  
  15. Using a number 20 Torx® bit, turn the throttle stop screw until the engine speed is 475-525 rpm in PARK (auto transmission) or 450-500 rpm in NEUTRAL (manual transmission).
  16.  
  17. Stop the engine and remove tool J-33047 from the throttle body.
  18.  
  19. Reconnect the TV cable to the throttle control bracket.
  20.  
  21. Reconnect the IAC valve connector.
  22.  
  23. Use silicone sealant to cover the throttle stop screw.
  24.  
  25. Reinstall the air cleaner.
  26.  



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Fig. Fig. 6: Installing tool J-33047

5.0L ENGINES
  1. Remove the idle stop screw plug or cap.
  2.  
  3. Ground the diagnostic connector (ALDL).
  4.  
  5. Turn the ignition ON and wait 45 seconds, DO NOT start the engine.
  6.  
  7. Disconnect the idle air control connector with the ignition ON .
  8.  
  9. Remove the ground from the diagnostic connector and disconnect the distributor set-timing connector.
  10.  
  11. Connect a tachometer to the engine.
  12.  
  13. Place the transmission in PARK (auto transmission) or NEUTRAL (manual transmission). Start and run the engine until it reaches normal operating temperature.
  14.  

It is important that the distributor set-timing connector be disconnected to fix the spark advance at base timing. This eliminates the possibility of changes in engine speed due to variations in timing.

  1. The idle speed should be 450-500 rpm, adjust as necessary.
  2.  


WARNING
Correct minimum idle speed adjustment is critical to vehicle performance and component durability. Incorrect minimum idle speed adjustment (too high) will cause the IAC valve pintle to constantly bottom in it's seat and result in early valve failure. If minimum idle speed is adjusted too low, the vehicle may not start in cold weather or may stall during warm-up.

  1. Turn the ignition OFF and reconnect the IAC motor connector.
  2.  
  3. Reconnect the distributor set-timing connector.
  4.  
  5. Use silicone sealant to cover the throttle stop screw.
  6.  

Throttle Position Sensor (TPS)

1982-1983 2.5L TBI engines are equipped with an adjustable throttle position sensor. This procedure should only be performed after replacing the TPS or diagnosis leads to incorrect TPS adjustment.

  1. Remove the throttle position sensor connector and install three jumper wires between the connector and the sensor. Connect a digital voltmeter to terminals B and C .
  2.  
  3. Turn the ignition ON . It should display between 0.45-0.60 volts.
  4.  
  5. Adjust the TPS, if necessary, by loosening the attaching screws and rotating the TPS.
  6.  
  7. Tighten the screws, remove the jumper wires with the ignition OFF and reconnect the harness connector.
  8.  
  9. Start the engine and check for proper idle operation.
  10.  



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Fig. Fig. 7: TPS adjustment

 
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