Fuel Delivery and Air Induction: Adjustments
Fig. 2 Propane enrichment specifications. 6-250 engine W/2SE carburetor:
6-250 ENGINE W/2SE CARBURETOR
The idle mixture screw is protected by a plug which prevents tampering during normal tune-up procedures. If it is evident that idle mixture requires adjustment, remove the plug as outlined under ``Concealment Plug Removal'' in the appropriate carburetor section. Idle mixture adjustment requires artificial propane enrichment. Propane enrichment tool J-26911 or equivalent, is required to adjust idle mixture. Air cleaner must remain in place during adjustments. A/C control, if equipped, must be in off position.
1. Set parking brake, then block drive wheels.
2. Disconnect and plug vacuum hoses as directed on vehicle emission label.
3. Check and, if necessary, adjust ignition timing.
4. Connect tachometer to engine following manufacturer's instructions, then start engine and allow to reach normal operating temperature.
5. Set curb idle speed to specifications.
6. Disconnect crankcase ventilation tube from air cleaner. Insert hose with rubber stopper from propane valve into opening in air cleaner. Propane cylinder must remain upright during adjustments, and cylinder must be adequately filled to ensure correct propane flow.
7. With engine idling in Drive (manual transmission in Neutral), slowly open propane valve while observing tachometer. Continue to open valve until RPM begins to drop, and note maximum enriched idle RPM.
8. If maximum enriched idle RPM is within specifications, Fig. 2, proceed to Step 14.
9. If enriched RPM is not within specifications, remove carburetor, then the concealment plug. Reinstall carburetor, then restart engine.
10. Turn mixture screw inward (clockwise) until lightly seated, then back out until engine will just run (approximately 3 turns).
11. Continue to back out mixture screw 1/8 turn at a time until maximum idle speed is obtained, then set idle speed to maximum enriched idle RPM. Maximum idle speed is idle RPM plus propane enrichment RPM.
12. Turn mixture screw inward (clockwise) until specified curb idle speed is obtained, then recheck maximum enriched RPM. If not within specifications, repeat steps above.
13. Check and, if necessary, adjust fast idle speed.
14. Turn ignition off, remove propane tool, then reconnect crankcase ventilation and vacuum hoses.
6-250 ENGINE W/E2SE CARBURETOR
The E2SE carburetor is used on 6-250 engines equipped with C3 (Computer Command Control) emission system. Because of this system control, special preliminary checks are required. Procedures must be followed exactly, in sequence, to ensure correct mixture adjustment.
PRE-SET PROCEDURE
1. Remove carburetor. Following the procedure outlined under ``Concealment Plug Removal'' in the appropriate carburetor section. Turn mixture screw clockwise until lightly seated, then back screw out 4 turns.
2. Check for presence of idle air bleed plug in air horn. If plug is missing, replace air horn. If plug is in place, do not remove.
3. Remove vent stack screen to gain access to lean-mixture screw in bottom of float bowl.
4. Turn lean mixture screw in (clockwise) until lightly seated, then back screw out 2-1/2 turns.
5. Install carburetor on engine with air cleaner off and related vacuum fittings plugged.
6. Disconnect bowl vent hose at carburetor. Disconnect and plug vacuum hoses at EGR valve and ``T'' fitting in bowl vent hose. Disconnect canister purge hose at carburetor and plug vacuum fitting.
7. Remove secondary vacuum break thermal vacuum switch from air cleaner, then disconnect hose to thermostatic air cleaner from switch and plug fitting on switch. Leave all other vacuum hoses connected to switch.
8. Connect dwell meter positive lead to test lead (green wire) in MC solenoid harness and set meter on 6 Cylinder scale. Connect tachometer to engine following manufacturer's instructions.
9. Start engine and run at fast idle until engine enters ``Closed Loop'' mode of operation, indicated by a fluctuating dwell reading.
Fig. 3 Lean & idle mixture screw locations. 6-250 engine W/E2Se carburetor:
MIXTURE ADJUSTMENT PROCEDURE
Perform adjustments with automatic transmission in Park and manual transmission in Neutral, unless otherwise noted.
1. Start engine and run on high step of fast idle cam until system goes closed loop.
2. Run engine at 3000 RPM and adjust lean mixture screw (1), Fig. 3, as needed to obtain a dwell reading of 35°. If reading is too low, turn screw counterclockwise; if reading is too high, turn screw clockwise. Turn screw in small increments, allowing time between adjustments for engine and dwell meter to stabilize. If unable to adjust to specifications, inspect main metering circuit for leaks or restrictions. The dwell reading from the Mixture Control (MC) solenoid is used as an adjustment calibration. While it is normal for dwell readings to fluctuate over a 5° range, temporary mixture variations may cause dwell readings to vary as much as 10°-15°. Dwell readings specified for adjustment are the average of the most consistent variation. Therefore, it is most important to allow engine to stabilize before taking dwell readings.
3. Allow engine to return to idle.
4. Adjust idle mixture screw (2), Fig. 3, as needed to obtain an average dwell reading of 25°. If reading is too low, turn screw counterclockwise; if too high, turn screw clockwise. If unable to adjust to specifications, inspect idle system for leaks or restrictions.
5. Disconnect wiring harness connector to MC solenoid and observe tachometer. Engine speed should change at least 50 RPM. If not, check idle air bleed circuit for leaks or restrictions.
6. Run engine at 3000 RPM and observe dwell meter. Dwell should fluctuate, with an average reading of 35°. If reading is not as specified, repeat steps 2 through 4.
7. Reinstall vent screen stack, reconnect vacuum hoses to proper fittings and install air cleaner. Check and adjust, if necessary, curb idle speed.