Idle Mixture Adjustment
Fig. 5 Idle air bleed valve cover removal:
Fig. 6 Idle air bleed valve identification:
1. Connect dwell meter to test lead in MC solenoid harness (usually a green wire) and set meter on 6 cylinder scale. Connect tachometer to engine following manufacturer's instructions.
2. Disconnect and plug vacuum hoses as directed by underhood vehicle emissions label.
3. Start engine and run until it reaches normal operating temperature and dwell reading begins to fluctuate. Adjustments must be made with C3 system operating in ``Closed Loop'' mode, indicated by a fluctuating dwell reading. It is essential that coolant temperature and oxygen sensors be at operating temperature during adjustments. Some engines may enter ``Open Loop'' mode at idle (indicated by fixed dwell reading), due to cooling of oxygen sensor. In this case, place transmission in neutral and run engine at fast idle until dwell reading begins to fluctuate.
4. Place transmission in Drive (manual transmission in Neutral) and check curb idle speed. If curb idle speed is not within specifications on models equipped with Idle Speed Control (ISC) refer to ``Idle Speed Control (ISC) Adjustment'' for adjustment procedure.
5. With engine at specified curb idle speed, dwell meter should indicate a fluctuating reading with a 10°-50° range.
6. If dwell reading is within specifications, mixture adjustment is correct.
7. If dwell reading is not within specifications, remove cover from idle air bleed valve, Fig. 5:
a. Stop engine and cover carburetor air intake, vents, etc. to prevent metal chips from entering engine.
b. Carefully center a No. 35 drill (.110 inch) on one of the rivets securing bleed valve cover. Drill only enough to remove rivet head, then repeat with remaining rivet.
c. Drive rivet stems out of air bleed valve tower with a small punch. Remove and discard cover.
d. Remove pieces of rivet from bleed valve tower, then blow out any dirt or metal chips that may have entered bleed valve cavity.
8. On 1983-84 models, Examine top of air bleed valve for an identification letter, Fig. 6, and proceed as follows:
a. If no letter is stamped on valve, proceed to ``Mixture Adjustment A.''
b. If a letter is stamped on valve, proceed to ``Mixture Adjustment B.''
9. On 1985-87 Caballero and El Camino models, proceed to ``Mixture Adjustment C.''
Fig. 7 Idle air bleed valve adjustment:
Fig. 8 Idle mixture screw base adjustment. 1983-84 E4ME carburetors less letter stamping:
MIXTURE ADJUSTMENT A
1. Install gauging tool J-33815-2 or equivalent in ``D'' shaped hole on throttle side of air horn, Fig. 7, with end of tool positioned above open cavity next to idle air bleed valve.
2. Hold gauge down lightly to bottom MC solenoid plunger, then adjust idle air bleed valve so tool will pivot over and just contact top of valve. Remove gauging tool.
3. Start engine and run until it reaches normal operating temperature and dwell reading begins to fluctuate.
4. Place automatic transmission in Drive (manual transmission in Neutral) and adjust idle air bleed valve to obtain a fluctuating dwell reading between 25° and 35° (as close to 30° as possible), at specified curb idle speed. Bleed valve is very sensitive to adjustment. Adjust valve in small increments, allowing time between adjustments for engine to stabilize.
5. If unable to adjust dwell reading to specifications, or if reading does not fluctuate, remove plugs covering idle mixture screws as outlined under ``Concealment Plug Removal'' in the appropriate carburetor section.
6. Turn each mixture screw in (clockwise) until lightly seated, then back screws out specified number of turns, Fig. 8.
7. Reinstall carburetor using a new gasket, with air cleaner removed, and vacuum hoses disconnected and plugged as outlined on underhood vehicle emissions label.
8. Repeat steps 3 and 4. If unable to obtain specified dwell reading, proceed as follows:
a. If reading is below 25°, turn mixture screws counterclockwise 1 turn, then repeat steps 3 and 4.
b. If reading is above 35°, turn mixture screws clockwise 1 turn, then repeat steps 3 and 4.
c. If unable to adjust dwell to specifications, or if reading does not fluctuate, refer to C3 System Section.
9. Stop engine. Seal mixture screw cavities with RTV sealer and install bleed valve cover.
10. Reinstall air cleaner and reconnect vacuum hoses, then check curb idle speed.
Fig. 7 Idle air bleed valve adjustment:
MIXTURE ADJUSTMENT B
1. Install gauging tool J-33815-2 or equivalent in ``D'' shaped hole on throttle side of air horn, Fig. 7, with end of tool positioned above open cavity next to idle air bleed valve.
2. Hold gauge down lightly to bottom MC solenoid plunger and adjust idle air bleed valve so that tool will pivot over and just contact top of valve. Remove gauging tool.
3. Remove plugs covering idle mixture adjusting screws as outlined under ``Concealment Plug Removal'' in the appropriate carburetor section. Turn mixture screws in (clockwise) until lightly seated, then back screws out 3 turns.
4. Reinstall carburetor using a new gasket, with air cleaner removed and vacuum hoses disconnected and plugged as outlined on underhood vehicle emissions label.
5. Start engine and run until it reaches normal operating temperature and dwell begins to fluctuate.
6. Place automatic transmission in Drive (manual transmission in Neutral) and adjust mixture screws equally to obtain a fluctuating dwell reading between 25° and 35° (as close to 30° as possible). Turn mixture screws equally, 1/8 turn per adjustment, allowing time between adjustments for engine to stabilize. If dwell reading is below 25°, turn screws counterclockwise; if reading is above 35° turn screws clockwise.
7. If unable to obtain specified dwell reading, refer to C3 System Section.
8. Stop engine. Seal mixture screw cavities with RTV sealer and install idle air bleed valve cover.
9. Install air cleaner and reconnect vacuum hoses, then ensure curb idle speed is within specifications.
MIXTURE ADJUSTMENT C
1. Install gauging tool J-33815-2, BT-8253-B or equivalent in ``D'' shaped hole on throttle side of air horn, with end of tool positioned above open cavity next to idle air bleed valve.
2. Hold gauge down lightly to bottom MC solenoid plunger and adjust idle air bleed valve so that tool will pivot over and just contact top of valve. Remove gauging tool.
3. Disconnect and plug hose at canister purge valve, start engine and run until it reaches normal operating temperature.
4. With engine at specified curb idle speed in drive (neutral for manual transmission models), slowly adjust idle air bleed valve to obtain a fluctuating dwell meter reading within the 25-35° range, as close to 30° as possible. Turn valve 1/8 of a turn at a time, clockwise or counterclockwise as needed, allowing time between each adjustment for dwell reading to stabilize.
5. If specified dwell reading cannot be obtained, stop engine and remove plugs covering idle mixture adjusting screws as outlined under ``Concealment Plug Removal'' in the appropriate carburetor section.
6. Turn each mixture screw in (clockwise) until lightly seated, then back screws out 3 turns.
7. Reinstall carburetor, leaving air cleaner removed and vacuum hoses disconnected as outlined on underhood emissions label.
8. Start engine and run until it reaches normal operating temperature, then perform idle air bleed valve adjustment as outlined in step 4.
9. If specified dwell reading cannot be obtained, proceed as follows:
a. If dwell reading is less than 25°, turn each mixture screw counterclockwise one turn, then repeat step 4.
b. If dwell reading is greater than 35°, turn each mixture screw clockwise one turn, then repeat step 4. If specified dwell reading still cannot be obtained, check for C3 system malfunction as outlined in ``System Performance Check.''
10. Seal idle mixture adjusting screw cavities with RTV sealer and ensure that idle speed is within specification.
MIXTURE ADJUSTMENT
1. Remove plugs covering idle mixture adjusting screws as outlined under ``Concealment Plug Removal'' in the appropriate carburetor section.
2. Turn each mixture adjusting screw in (clockwise) until lightly seated, then back screws out 3 turns.
3. Reinstall carburetor, leaving air cleaner off and applicable vacuum fittings plugged.
4. Connect dwell meter to MC solenoid test lead and set meter on 6 cylinder scale.
5. Disconnect and plug hose to canister purge valve, start engine and run until it reaches normal operating temperature.
6. Place transmission in drive (neutral for manual transmission) and ensure that curb idle speed is within specifications.
7. Adjust idle mixture screws equally, turning each screw 1/8 of a turn at a time, until dwell reading fluctuates in the 25-35° range, as close to 30° as possible. Allow time between each adjustment for dwell readings to stabilize. If readings are less than 25°, rotate screws counterclockwise; if readings are above 35°, rotate screws clockwise.
8. When specified dwell reading has been obtained, ensure that curb idle speed is within specifications, then seal mixture adjusting screw cavities with RTV sealer. If specified dwell readings cannot be obtained after completing calibration procedure, disassemble and repair carburetor as needed.