GM Firebird 1982-1992 Repair Guide

Throttle Body

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REMOVAL & INSTALLATION



Front Unit
  1. Relieve the fuel system pressure.
  2.  
  3. Remove the air cleaner assembly, noting the connection points of the vacuum lines.
  4.  
  5. Detach the electrical connectors at the injector and the idle air control motor.
  6.  
  7. Disconnect the vacuum lines from the TBI unit, noting the connection points. During installation, refer to the underhood emission control information decal for vacuum line routing information.
  8.  
  9. Disconnect the transmission detent cable from the TBI unit.
  10.  
  11. Disconnect the fuel inlet (feed) and fuel balance line connections at the front TBI unit.
  12.  
  13. Remove and discard the throttle control rod retaining clip from the front TBI throttle lever stud. A new clip must be used during reassembly.
  14.  
  15. Unbolt and remove the TBI unit.
  16.  

To install:
  1. Replacement of the manifold cover or either throttle body requires throttle valve synchronizing and checking of the throttle rod alignment (see "Preliminary Adjustments''). Before installing the replacement throttle body unit(s) on the engine, perform the following steps:
    1. If the tamper resistant plugs covering the throttle stop screws are in place, remove the plugs.
    2.  
    3. If the front TBI unit throttle synchronizing screw has a welded retaining collar, grind off the weld.
    4.  
    5. Block possible movement of the throttle lever, relieving the force of the heavy spring against the throttle synchronizing screw. This prevents the levers from coming into contact.
    6.  

  2.  

If the lever is not blocked before the throttle synchronizing screw is removed, the screw may be damaged, and reinstallation will be accomplished only with great difficulty.

    1. Remove the synchronizing screw and collar. Discard the collar and reinstall the screw. The blocking from the throttle lever (installed in the previous step) can now be removed.
    2.  



CAUTION
The collar must be removed to prevent possible interference with the air cleaner. Failure to do so could result in personal injury.

  1. Use new gaskets and tighten the TBI bolts to 120-168 inch lbs. (13-19 Nm) during installation.
  2.  
  3. Perform the preliminary adjustments. These procedures must be followed before further assembly.
  4.  
  5. Reconnect the fuel lines to the TBI units. Use a backup wrench to prevent the nuts from turning in the TBI unit.
  6.  
  7. Reconnect the throttle cable and detent cable.
  8.  
  9. Reconnect all related vacuum lines.
  10.  
  11. Reconnect the electrical connectors.
  12.  
  13. With the engine OFF, depress the accelerator pedal to the floor and release. Check for free return of the pedal.
  14.  
  15. Check the throttle position sensor voltage and adjust if necessary.
  16.  
  17. Perform the Minimum Idle and Throttle Valve Synchronization adjustment procedures.
  18.  

Rear Unit

  1. Relieve the fuel system pressure.
  2.  
  3. Remove the air cleaner assembly, noting the connection points of the vacuum lines.
  4.  
  5. Disconnect the electrical connectors at the injector, idle air control motor, and throttle position sensor.
  6.  
  7. Disconnect the vacuum lines from the TBI unit, noting the connection points. During installation, refer to the underhood emission control information decal for vacuum line routing information.
  8.  
  9. Disconnect the throttle and cruise control (if so equipped) cables at the TBI unit.
  10.  
  11. Disconnect the fuel return and balance line connections from the rear TBI unit.
  12.  
  13. Remove and discard the throttle control rod retaining clip from the front TBI unit throttle lever stud. A new clip must be used during reassembly.
  14.  

One throttle rod end bearing is permanently attached to the throttle lever stud of the rear TBI unit, and must not be removed from it. If the throttle rod and bearing assembly needs replacement, The entire rear throttle body must be replaced.

  1. Unbolt and remove the TBI unit.
  2.  

To install:
  1. Replacement of the manifold cover or either throttle body requires throttle valve synchronizing and checking of the throttle rod alignment (see "Preliminary Adjustments''). Before installing the replacement throttle body unit(s) on the engine, perform the following steps:
    1. If the tamper resistant plugs covering the throttle stop screws are in place, remove the plugs.
    2.  
    3. If the front TBI unit throttle synchronizing screw has a welded retaining collar, grind off the weld.
    4.  
    5. Block possible movement of the throttle lever, relieving the force of the heavy spring against the throttle synchronizing screw. This prevents the levers from coming into contact.
    6.  

  2.  

If the lever is not blocked before the throttle synchronizing screw is removed, the screw may be damaged, and reinstallation will be accomplished only with great difficulty.

    1. Remove the synchronizing screw and collar. Discard the collar and reinstall the screw. The blocking from the throttle lever (installed in the previous step) can now be removed.
    2.  



CAUTION
The collar must be removed to prevent possible interference with the air cleaner. Failure to do so could result in personal injury.

  1. Use new gaskets and tighten the TBI bolts to 120-168 inch lbs. (13-19 Nm) during installation.
  2.  
  3. Perform the preliminary adjustments. These procedures must be followed before further assembly.
  4.  
  5. Reconnect the fuel lines to the TBI units. Use a backup wrench to prevent the nuts from turning in the TBI unit.
  6.  
  7. Reconnect the throttle cable and the cruise control cable.
  8.  
  9. Reconnect all related vacuum lines.
  10.  
  11. Reconnect the electrical connectors.
  12.  
  13. With the engine OFF, depress the accelerator pedal to the floor and release. Check for free return of the pedal.
  14.  
  15. Check the throttle position sensor voltage and adjust if necessary.
  16.  
  17. Perform the Minimum Idle and Throttle Valve Synchronization adjustment procedures.
  18.  

INJECTOR REPLACEMENT



See Figures 1, 2, 3 and 4

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.

  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. 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. Carefully rotate the injector fuel filter back and forth, then remove the filter from the base of the injector.
  6.  
  7. Remove the large O-ring and steel back-up washer at the top of the injector cavity in the fuel meter body.
  8.  
  9. Remove the small O-ring located at the bottom of the injector cavity.
  10.  

To install:
  1. Install the injector fuel filter on the nozzle end of the fuel injector, using a slight twisting motion to position the filter against the injector base.
  2.  

The filter is cone shaped. The large end of the filter faces up (towards the electrical terminals), so that the filter covers the raised rib at the base of the injector.

  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. Install the fuel meter cover using new gaskets and a new dust seal. The two short screws are located adjacent to the injector.
  4.  
  5. Attach 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. 1: Fuel meter cover removal



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Fig. Fig. 2: Injector removal



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Fig. Fig. 3: Injector components



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Fig. Fig. 4: Injector installation

ADJUSTMENTS



See Figures 5 through 9

Preliminary Adjustments

The preliminary adjustments are performed if tampering with the idle speed or synchronization is evident and when either of the throttle bodies or the manifold cover have been replaced. They must be performed BEFORE the Minimum Idle and Throttle Valve Synchronizing procedure.

THROTTLE VALVE SYNCHRONIZING
  1. Turn BOTH front and rear unit throttle stop screws counterclockwise enough to break contact with the related throttle lever tangs.
  2.  
  3. Adjust the throttle synchronizing screw to allow BOTH throttle valves to close. The throttle rod end bearing will move freely on the front unit throttle lever stud when both valves are closed.
  4.  
  5. Turn the front unit throttle stop screw clockwise slowly until it makes contact with the throttle lever tang. Turn the screw clockwise an additional 1 / 4 turn.
  6.  
  7. Turn the rear unit throttle stop screw clockwise slowly until it makes contact with the throttle lever tang. Turn the screw an additional 1 / 2 turn.
  8.  



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Fig. Fig. 5: Blocking the throttle levers



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Fig. Fig. 6: Throttle stop and synchronizing screws

THROTTLE ROD ALIGNMENT CHECK

The throttle rod alignment check procedure is followed only if a replacement manifold cover or TBI unit has been installed. If not, proceed to "Minimum Idle and Throttle Valve Synchronizing''.

  1. Actuate the rear unit throttle lever to bring both units to the wide open throttle position, loading the throttle valves. Move the throttle rod toward the front unit casting boss.
  2.  
  3. Check the clearance between the shoulder of the stud and the side of the ball surface. Maximum clearance must not exceed 0.200 in. (5mm). If the clearance is greater, the assembly (manifold cover, TBI unit or throttle body) must be replaced and the preliminary adjustments repeated.
  4.  
  5. Use needle-nose pliers to install a NEW throttle rod and bearing assembly retaining clip.
  6.  
  7. Move both front and rear throttle levers through the total throttle travel, loading both valves.
  8.  
  9. Check the clearance between the throttle rod and the front unit throttle body casting boss. If minimum clearance is less than 0.040 in. (1.02mm), the assembly must be replaced. If minimum clearance is at least 0.040 in. (1.02mm), proceed with assembly.
  10.  



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Fig. Fig. 7: Maximum shoulder-to-ball clearance check



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Fig. Fig. 8: Minimum throttle rod-to-casting clearance check

Minimum Idle and Throttle Valve Synchronizing

The throttle position of each throttle body must be balanced so that the throttle plates are synchronized and open simultaneously. These adjustment procedures must be followed AFTER performing the "Preliminary Adjustments''.

  1. Remove the air cleaner and plug the vacuum port on the rear TBI unit for the thermostatic air cleaner.
  2.  
  3. Remove the tamper resistant plugs covering both unit throttle stop screws, if necessary.
  4.  
  5. Block the drive wheels and apply the parking brake.
  6.  
  7. Connect a tachometer to measure rpm.
  8.  
  9. Start the engine and allow the engine rpm to stabilize at normal operating temperature.
  10.  
  11. Have a helper apply the brakes and place the transmission in DRIVE.
  12.  
  13. Plug the idle air passages of each throttle body with plugs (J-33047 or equivalent). Make sure the plugs are seated fully in the passage so that no air leaks exist. The engine rpm should decrease below curb idle speed. If the engine rpm does not decrease, check for a vacuum leak.
  14.  
  15. Remove the cap from the ported tube on the rear TBI unit and connect a vacuum gauge or water manometer.
  16.  
  17. Adjust the rear unit throttle stop screw to obtain approximately 1 / 2 in. Hg as read on the vacuum gauge, or 6 in. H 2 O as read on the manometer. If not able to adjust to this level, check that the front unit throttle stop is not limiting throttle travel.
  18.  
  19. Remove the vacuum gauge or manometer from the rear unit and install the cap on the ported vacuum tube.
  20.  
  21. Remove the cap from the ported vacuum tube on the front TBI unit and install the gauge or manometer as before. If the reading is not the same as the rear unit, proceed as follows:
    1. Locate the throttle synchronizing screw and collar on the front TBI unit. The screw may be welded to discourage tampering with this adjustment. Break the weld, if necessary, and install a new screw with a thread sealing compound applied.
    2.  
    3. Adjust the screw to obtain approximately 1 / 2 in. Hg as read on the vacuum gauge, or 6 in. H 2 O on the manometer.
    4.  

  22.  
  23. Remove the gauge or manometer from the ported tube and reinstall the cap.
  24.  
  25. Adjust the rear throttle stop screw to obtain 475 rpm, with the transmission in D and the parking brake applied. On manual transmission models, leave the gear selector in N .
  26.  
  27. Turn the ignition OFF and place automatic transmission in N .
  28.  
  29. Remove idle air passage plugs.
  30.  
  31. Start the engine. It may run at a high rpm but the engine speed should decrease when the idle air control valves close the air passages. Stop the engine when the rpm decreases.
  32.  
  33. The throttle position sensor (TPS) voltage should be checked and adjusted, if necessary.
  34.  
  35. Connect the vacuum line to the TBI unit and install the air cleaner.
  36.  
  37. Reset the idle speed control motors by driving the vehicle to 45 mph.
  38.  

Throttle Position Sensor (TPS)

An accurate digital voltmeter is needed to perform this adjustment.

  1. Remove the air cleaner.
  2.  
  3. Disconnect the TPS electrical connector.
  4.  
  5. Install three jumper wires between the TPS and the TPS wiring terminal connections.
  6.  
  7. Turn the ignition ON, engine stopped, measure the voltage between terminals B and C.
  8.  
  9. The display should read between 0.45-0.60 volts.
  10.  
  11. Loosen the screws and rotate the TPS to obtain the correct voltage, if necessary.
  12.  
  13. Tighten the TPS screws and turn the ignition OFF. Remove the jumpers.
  14.  
  15. Reconnect the wiring to the TPS.
  16.  
  17. Install the air cleaner.
  18.  



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Fig. Fig. 9: TPS adjustment

 
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