Fuel Delivery and Air Induction: Adjustments
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.
1985-86 California 10-30 & 1500-3500 Series (C3 System)
The C3 emission system used on these engines provides precise control of air/fuel mixtures during all ranges of engine operation. Because of this system control, special adjustment procedures must be used and followed in exact sequence to ensure proper mixture adjustment. Mixture adjustment should only be performed after carburetor overhaul or if indicated by C3 ``System Performance Check''. Dwell readings from the Mixture Control (MC) solenoid are used to determine carburetor calibration.
MC SOLENOID EXTERNAL GAUGE CHECK
MC solenoid travel must be within specifications before idle mixture can be adjusted. Perform check with engine off and air cleaner removed. Before proceeding, modify float gauge J-34935-1, BT-8420-A or equivalent to fit in ``D'' shaped vertical vent in carburetor air horn.
1. Insert gauge in ``D'' shaped vent hole, press down on gauge and release, ensuring that gauge moves freely without binding.
2. With gauge released (solenoid up position), read gauge at eye level and record reading that lines up with top of air horn casting.
3. Press down lightly on gauge until bottomed and record reading where gauge lines up with top of air horn casting.
4. Subtract reading in step 2 from reading in step 3 to obtain total MC solenoid travel.
5. If total travel is 2/32 to 6/32 inch and dwell reading at 3000 RPM obtained during ``System Performance Check'' was within specifications (10° to 50°), proceed to ``Idle Air Bleed Valve Adjustment.''
6. If total MC solenoid travel is not within specifications of if incorrect dwell reading is obtained at 3000 RPM during ``System Performance Check,'' perform ``MC Solenoid Adjustment.''
Fig. 9 Install mixture control solenoid gauge tool:
Fig. 10 Adjusting mixture control solenoid:
MC SOLENOID ADJUSTMENT
1. Remove carburetor air horn and gasket, solenoid adjusting screw, rich limit stop, MC solenoid plunger, metering rods and springs, plastic filler block and MC solenoid.
2. Install gauging tool J-33815-1, BT-8253-A or equivalent over throttle side metering jet rod guide, Fig. 9, then temporarily reinstall solenoid adjusting screw spring, solenoid, solenoid plunger, rich limit stop and solenoid adjusting screw.
3. Hold solenoid plunger in down position and rotate adjusting screw clockwise until plunger contacts gauging tool. Use tool J-28696-10, BT-7928 or equivalent to turn solenoid adjusting screw.
4. Continue holding plunger down and slowly turn adjusting screw counterclockwise until plunger breaks contact with gauging tool. Adjustment is correct when solenoid plunger just contacts both the solenoid stop and the gauging tool, Fig. 10.
5. Note position of adjusting tool handle, then turn adjusting screw clockwise until bottomed, recording number of turns necessary.
6. Remove adjusting screw, rich limit stop, MC solenoid and plunger, adjusting screw spring and gauging tool.
7. Install adjusting screw spring, MC solenoid, filler block, metering rods and springs, solenoid plunger, rich limit stop and adjusting screw.
8. Rotate adjusting screw clockwise until MC solenoid bottoms in float bowl, then turn adjusting screw counterclockwise the exact number of turns recorded in step 5.
9. Reinstall carburetor air horn using new gasket, then perform ``System Performance Check'' as outlined in C3 System Section..
10. If dwell readings are within specifications, no further adjustment is necessary. If dwell readings are not as specified, perform ``Idle Air Bleed Valve Adjustment.''
Fig. 11 Idle air bleed valve adjustment:
IDLE AIR BLEED VALVE ADJUSTMENT
Idle air bleed valve should only be adjusted when removal is required for cleaning or replacement or if C3 ``System Performance Check'' indicates the carburetor as cause for driveability complaint.
1. Remove idle air bleed valve cover as follows:
a. Remove air cleaner and gasket, then cover bowl vents and air inlets to prevent metal chips from entering carburetor.
b. Carefully drill out rivet heads securing cover, then drive out rivet shanks using suitable drift.
c. Remove cover and tape used to cover bowl vents and air passages.
2. Install gauging tool J-33815-2, BT-8253-B or equivalent in throttle side ``D'' shaped vent hole, Fig. 11, with upper end of tool positioned over open cavity next to bleed valve.
3. Hold gauging tool down lightly so that solenoid plunger is held against stop, then adjust bleed valve so that gauge tool will pivot over and just contact top of valve.
4. Remove gauging tool and perform C3 ``System Performance Check.''
5. If dwell readings are within specifications, no further adjustment is necessary. If readings are not as specified, perform ``Mixture Adjustment.''
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.