H2_RECOVERY
03-28-2006, 02:18 PM
BBD Carburetor - Rich/Lean Condition Diagnosis
JULY 1984
000 239
AMC/JEEP MODELS
18E
SIX-CYLINDER ENGINE
Attention: Workshop, Parts Department
BBD CARBURETOR DIAGNOSIS
Information
This I.S. Note contains additional information on diagnosing an overly rich or lean condition in the BBD carburetor used on six-cylinder AMC and Jeep models.
A choke or stepper motor malfunction can result in overly rich or lean fuel mixtures. Too rich a mixture can result in excessive fuel consumption and a rough idle after warmup. Too lean a mixture can result in hard cold starts and poor acceleration before and after warmup. These conditions would be particularly evident in cold weather operation.
If initial diagnosis indicates that the choke system is functioning properly, check for a stepper motor malfunction as follows.
Procedure
1. Remove carburetor air cleaner cover.
2. On 1981-82 models, look through carburetor air horn and observe movement of stepper motor upper metering pin as helper turns ignition switch to On position (do not start engine). Pin should move fully forward, reverse direction and move part way toward rear, then stop and remain stationary.
a. If pin functions properly, proceed to next step.
b. If pin movement is not as described, or pin is obviously binding, proceed to step 5.
NOTE: Although the two metering pins operate in tandem, only the upper pin is visible through the air horn.
4. On 1983-84 models, remove air cleaner cover and install clear plastic safety viewing shield on air cleaner. Then look through air horn and observe movement of stepper motor upper metering pin as helper starts engine. Pin should move fully forward, reverse direction and move part way toward rear, stop momentarily, then move forward additional steps.
WARNING: Do not perform this test without a 1/4-inch thick, 15-inch diameter clear plastic safety viewing shield on the air cleaner. Also keep clear of hot and/or rotating engine components while observing metering pins.
a. If pin functions properly but some kind of performance problem was experienced, further diagnosis is necessary. Refer to appropriate service manual.
b. If pin movement is not as described, or pin sticks in forward or rearward position, proceed to step 5.
5. Remove carburetor and remove stepper motor from carburetor. Reconnect stepper motor and observe pin movement as helper turns ignition to On position.
a. If pins now move full forward then half-way back, replace stepper motor with new motor 813 2632.
b. If pins move only slightly, or shuttle back and forth, or stick in full forward or rearward position, replace stepper motor with new motor described in step a.
c. If pins do not move at all, perform initialization test outlined in CEC system Diagnostic step 1 in appropriate service manual before replacing stepper motor. Problem may be in stepper motor feed circuit.
NOTE: When installing stepper motor, tilt carburetor so that stepper motor opening is facing downward before inserting motor. Also be sure stepper motor pins and centering spring are fully engaged before installing stepper motor retaining bolts.
Parts
Description Quantity Part Number
MOTOR, Stepper (Actuator) 1 813 2632
S.R.T. INFORMATION
Operation
Operation Description T.I.C. Number S.R.T.
CO. CARBURETOR - R&R 1-357 1098 0.8
Inc. adjust idle, check stepper motor operation and replace gaskets
CO. ACTUATOR, ENRICHMENT - 1-357 1686 0.4
REPLACE Stepper motor or duty cycle solenoid
Filing Instructions
File this I.S. Note in your M.R. 171 binder.
JULY 1984
000 239
AMC/JEEP MODELS
18E
SIX-CYLINDER ENGINE
Attention: Workshop, Parts Department
BBD CARBURETOR DIAGNOSIS
Information
This I.S. Note contains additional information on diagnosing an overly rich or lean condition in the BBD carburetor used on six-cylinder AMC and Jeep models.
A choke or stepper motor malfunction can result in overly rich or lean fuel mixtures. Too rich a mixture can result in excessive fuel consumption and a rough idle after warmup. Too lean a mixture can result in hard cold starts and poor acceleration before and after warmup. These conditions would be particularly evident in cold weather operation.
If initial diagnosis indicates that the choke system is functioning properly, check for a stepper motor malfunction as follows.
Procedure
1. Remove carburetor air cleaner cover.
2. On 1981-82 models, look through carburetor air horn and observe movement of stepper motor upper metering pin as helper turns ignition switch to On position (do not start engine). Pin should move fully forward, reverse direction and move part way toward rear, then stop and remain stationary.
a. If pin functions properly, proceed to next step.
b. If pin movement is not as described, or pin is obviously binding, proceed to step 5.
NOTE: Although the two metering pins operate in tandem, only the upper pin is visible through the air horn.
4. On 1983-84 models, remove air cleaner cover and install clear plastic safety viewing shield on air cleaner. Then look through air horn and observe movement of stepper motor upper metering pin as helper starts engine. Pin should move fully forward, reverse direction and move part way toward rear, stop momentarily, then move forward additional steps.
WARNING: Do not perform this test without a 1/4-inch thick, 15-inch diameter clear plastic safety viewing shield on the air cleaner. Also keep clear of hot and/or rotating engine components while observing metering pins.
a. If pin functions properly but some kind of performance problem was experienced, further diagnosis is necessary. Refer to appropriate service manual.
b. If pin movement is not as described, or pin sticks in forward or rearward position, proceed to step 5.
5. Remove carburetor and remove stepper motor from carburetor. Reconnect stepper motor and observe pin movement as helper turns ignition to On position.
a. If pins now move full forward then half-way back, replace stepper motor with new motor 813 2632.
b. If pins move only slightly, or shuttle back and forth, or stick in full forward or rearward position, replace stepper motor with new motor described in step a.
c. If pins do not move at all, perform initialization test outlined in CEC system Diagnostic step 1 in appropriate service manual before replacing stepper motor. Problem may be in stepper motor feed circuit.
NOTE: When installing stepper motor, tilt carburetor so that stepper motor opening is facing downward before inserting motor. Also be sure stepper motor pins and centering spring are fully engaged before installing stepper motor retaining bolts.
Parts
Description Quantity Part Number
MOTOR, Stepper (Actuator) 1 813 2632
S.R.T. INFORMATION
Operation
Operation Description T.I.C. Number S.R.T.
CO. CARBURETOR - R&R 1-357 1098 0.8
Inc. adjust idle, check stepper motor operation and replace gaskets
CO. ACTUATOR, ENRICHMENT - 1-357 1686 0.4
REPLACE Stepper motor or duty cycle solenoid
Filing Instructions
File this I.S. Note in your M.R. 171 binder.