Engine - Miss/Hesitation/Stalls/MIL ON

91ford22

Article No.
91-14-4

07/11/91


^ IDLE - ROUGH OR ROLLING - 3.8L (BASE) AND 5.0L
HO - VEHICLES BUILT FROM JOB # 1 TO 1/28/91
AND 3.8L SC - VEHICLES BUILT FROM JOB # 1 TO 3/4/91

^ MISS, HESITATION, STUMBLE, LACK OF POWER - 3.8L
(BASE) AND 5.0L HO - VEHICLES BUILT FROM JOB # 1
TO 1/28/91 AND 3.8L SC - VEHICLES BUILT FROM
JOB # 1 TO 3/4/91

^ STALLS - DURING IDLE, ACCELERATION, CRUISE OR
DECELERATION - 3.8L (BASE) AND 5.0L HO -
VEHICLES BUILT FROM JOB # 1 TO 1/28/91 AND
3.8L SC - VEHICLES BUILT FROM JOB # 1 TO 3/4/91

^ LAMP - "CHECK ENGINE" MALFUNCTION INDICATOR
LIGHT (MIL) ILLUMINATED - SERVICE CODES 173 AND
177 STORED IN MEMORY - 3.8L (BASE) AND 5.0L
HO - VEHICLES BUILT FROM JOB # 1 TO 1/28/91
AND 3.8L SC - VEHICLES BUILT FROM JOB # 1 TO 3/4/91


FORD: 1991 THUNDERBIRD

LINCOLN-MERCURY: 1991 COUGAR


ISSUE: The "Check Engine" Malfunction Indicator Light may be illuminated and service codes 173 and 177 stored in memory. In addition, various driveability symptoms such as those listed below may be present.

^ Stalls - During idle, acceleration, cruise or deceleration

^ Idle - Rough or rolling

^ Misses - Buck and jerks, hesitation, stumble and lack of power

The MIL activation and the miscellaneous driveability symptoms may be caused by a faulty Heated Exhaust Gas Oxygen (HEGO) sensor.

ACTION: Replace the HEGO sensors if, after performing the diagnostics in the 1991 Engine/Emissions-Diagnosis Shop Manual, it is determined that they are faulty. Refer to the following procedures for service details.





3.8L (BASE) AND 5.0L HO ENGINE

1. Check to see if the vehicle has a (F17F-9F472-AA) HEGO sensor (Part number is on sensor). If so, replace both sensors.

2. If the vehicle has a (F0SF-9F472-AA) HEGO sensor (Same as new service part F1SZ-9F472-A), replace only the faulty sensor.

3.8L (SUPERCHARGED) ENGINE

1. Check to see if the vehicle has a (F17F-9F472-AA) HEGO sensor (Part number is on sensor). If so, replace both sensors and install a new service processor.

2. If the vehicle has a (F0SF-9F472-AA) HEGO sensor (Same as new service part F1SZ-9F472-A), replace only the faulty sensor. Do not replace the processor.





Obtain an Authorized Modifications Decal and list the date, dealer number, and summary of alterations performed. Select a prominent place adjacent to the Vehicle Emission Control Information Decal suitable for installing the Authorized Modifications Decal. Clean the area, install the decal, and cover it with a clear plastic decal shield.


OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under Basic Warranty Coverage, Emissions Warranty Coverage
OPERATION DESCRIPTION TIME
911404A Perform Diagnosis And 0.6 Hr.
Replace One HEGO Sensor
- 3.8L EFI
911404B Perform Diagnosis And 0.9 Hr.
Replace Both HEGO Sensors
- 3.8L EFI
911404C Perform Diagnosis And 0.6 Hr.
Replace One HEGO Sensor
- 3.8L SC
911404D Perform Diagnosis And 1.2 Hr.
Replace Both HEGO
Sensors - 3.8L SC
911404E Perform Diagnosis And 0.4 Hr.
Replace One HEGO Sensor
- 5.0L HO
911404F Perform Diagnosis And 1.2 Hr.
Replace Both HEGO
Sensors - 5.0L HO
DEALER CODING
BASIC PART NO. CONDITION CODE
9F472 42
OASIS CODES: 206000, 607000, 607400, 607500, 607600, 607700, 608000, 608400, 609000, 609400, 609500, 609600, 610000, 610500, 611000, 611500, 614000, 614500, 614600