Diesel Data: Automotive Repair
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Mixture Control Solenoid: Adjustments

Fig. 3 Carburetor mixture control solenoid adjustment. V6-229 & 231 w/E2MC-ME carburetor:




Fig. 4 Lean & rich mixture screw plugs. V6-229 & 231 w/E2MC-ME carburetor:




Fig. 5 Lean & rich mixture screw plug installation. V6-229 & 231 w/E2MC-ME carburetor:





MC solenoid travel must be within specifications before idle mixture can be adjusted. Perform check with engine off and air cleaner removed. Before proceeding, use float gauge J-34935-1 or equivalent, to fit in ``D'' shaped vertical vent on carburetor air horn.
1. Insert gauge in ``D'' shaped hole. Press down on gauge and release, making sure 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. 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 MC solenoid travel is 2/32-6/32 inch, proceed to ``Idle Air Bleed Valve Adjustment.'' If travel is not within specifications, MC solenoid must be adjusted.

MC SOLENOID ADJUSTMENT

1. Remove carburetor air horn and gasket, MC solenoid plunger and plastic filler block.
2. Remove throttle side metering rod.
3. Install MC solenoid gauging tool J-33815-1 or equivalent over metering rod jet guide rod, Fig. 3, then re-install MC solenoid plunger.
4. Hold MC solenoid plunger in down position and turn lean mixture screw counterclockwise until plunger just breaks contact with gauging tool. Use tool J-28696 or equivalent to adjust lean mixture screw.
5. Slowly turn lean mixture screw clockwise until plunger just contacts gauging tool. Adjustment is correct when plunger contacts both solenoid stop and gauging tool, in down position. If adjusted position is less than 3/4 turn different than original position, original adjustment was correct.
6. Remove solenoid plunger and gauging tool, then reinstall metering rod and plastic filler block.
7. Remove rich mixture screw from underside of air horn.
8. Remove lean and rich mixture screw sealing plugs from air horn, Fig. 3, using a suitable punch.
9. Reinstall rich mixture screw turning until lightly seated, then back screw out 1/4 turn and reinstall air horn using a new gasket.
10. Adjust MC solenoid travel to 4/32 inch with rich mixture screw, checking as outlined in ``MC Solenoid Check.''
11. Install new plugs over lean and rich mixture screws as shown, Fig. 4, then proceed to ``Idle Air Bleed Valve Adjustment.'' New plugs must be installed, as directed, over lean and rich mixture screws in order to retain settings and to prevent fuel vapors from entering the atmosphere.


Fig. 6 Idle air bleed valve cover removal. V6-229 & 231 w/E2MC-ME carburetor:




Fig. 7 Idle air valve identification. V6-229 & 231 w/E2MC-ME carburetor:





IDLE AIR BLEED VALVE ADJUSTMENT

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 emission label.
3. Start engine and run until it reaches normal operating temperature and dwell reading begins to fluctuate. Adjustments must be made with C3 or C4 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 within 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. 6.
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. Examine top of air bleed valve for an identification letter, Fig. 7.
9. If no letter is stamped on valve, proceed to Mixture Adjustment A. If a letter is stamped on valve, proceed to Mixture Adjustment B.


Fig. 8 Idle air valve adjustment. V6-229 & 231 w/E2MC-ME carburetor:




Fig. 9 Idle mixture screw base adjustment position. V6-229 & 231 w/E2MC-ME carburetor:





MIXTURE ADJUSTMENT A

1. Install gauging tool J-33815-2 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, Fig. 8.
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. 9.
7. Reinstall carburetor using a new gasket, with air cleaner removed, and vacuum hoses disconnected and plugged as outlined on underhood vehicle emission 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. 8 Idle air valve adjustment. V6-229 & 231 w/E2MC-ME carburetor:





MIXTURE ADJUSTMENT B

1. Install gauging tool J-33815-2 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, Fig. 8.
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 emission 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 ``System Performance Check'' as outlined in the 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.



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