Concord L6-258 4.2L VIN C 2-bbl (1982)
Air/Fuel Mixture: By Symptom
Carburetor - Idle Mixture Adjustment
Models
All 1990 & Prior Domestic Vehicles With 4.2L I6 Engines With Fuel Feedback System
Subject
Idle Mixture Adjustment Procedure
Index
FUEL SYSTEM
Date
October 16, 1989
No.
14-53-89
P-3738 (C14-11-9)
BODY CODE LEGEND
ALL 1990 & PRIOR DOMESTIC VEHICLES WITH 4.2L I6 ENGINES WITH FUEL FEEDBACK SYSTEM
IDLE MIXTURE ADJUSTMENT FOR 4.2L I6 ENGINES
This Technical Service Bulletin is to advise dealer technicians of the procedure for carburetor idle mixture adjustment on all vehicles produced with the
4.2L I6 engine equipped with the fuel feedback system.
ADJUSTMENT PROCEDURE
NOTE:
THE IDLE MIXTURE ADJUSTMENT SHOULD ONLY BE PERFORMED IF THE ADJUSTMENT SCREWS WERE
REMOVED DURING CARBURETOR OVERHAUL FOR CLEANING PURPOSES.
WARNING:
USE EXTREME CAUTION WHEN THE ENGINE IS OPERATING. DO NOT STAND IN A DIRECT LINE WITH THE FAN.
DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS, OR FAN. DO NOT WEAR LOOSE CLOTHING.
1.
Set the parking brake firmly. Position the gear selector in NEUTRAL for manual transmissions and PARK for automatic transmissions.
2.
Connect a tachometer with an expanded scale of 400- 800 or 0-1000 RPM. Inspect periodically to ensure that the accuracy is within two percent.
Start the engine and warm it to the normal operating temperature.
3.
Stop engine. Restart engine and disconnect stepper motor connector within 15 seconds of engine restart. Stepper motor will be in the
initialized/midpoint position. PLEASE NOTE THAT THIS STEP SHOULD BE INSERTED INTO THE "IDLE MIXTURE ADJUSTMENT"
PROCEDURE AS WRITTEN IN THE SERVICE MANUAL.
4.
Position the gear selector in NEUTRAL for manual transmissions and DRIVE for automatic transmissions.
5.
Adjust the idle speed as described in the "Idle Speed Adjustment" procedure of the Service Manual. Adjust to the Curb Idle Speed "SetTo" RPM
listed in Specifications.
6.
Adjust the mixture screw(s) leaner (clockwise) until a perceptible loss in RPM is noted.
7.
Turn the mixture screw(s) richer (counterclockwise) until the highest RPM indication is obtained. Do not turn the screw(s) any further than the
point at which the highest RPM is first obtained. This point is referred to as LEAN BEST IDLE. The engine speed will increase above the curb
idle speed by an amount that corresponds to approximately the IDLE DROP specification to be obtained in the next step.
8.
As a final adjustment, turn the mixture screws clockwise (leaner) to obtain the specified drop in engine idle RPM. Turn both of the idle mixture
screws in small, equal amounts until the specified IDLE DROP is achieved. Refer to the Mixture Adjustment in the appropriate Service Manual.
9.
Reconnect the stepper motor connector.
