Engine - Surge Chuggle On Decel/Rough Idle

BULLETIN NUMBER:
91-6E-193

SECTION:
6E

NUMBER:
1

CORPORATE
REFERENCE NUMBER:
036516R

DATE:
October 1992



SUBJECT:
SURGE OR CHUGGLE ON DECEL AND/OR ROUGH IDLE (REPLACE ECM AND PROM)

MODELS:
1990-91 S/T TRUCKS WITH 4.3L ENGINE (RPO LB4) AND 5LM60 M/T TRANSMISSION



CONDITION:

Owners of some 1990-1991 S/T trucks equipped with 5-speed manual transmissions may comment about one or more of the following conditions:

- An engine deceleration surge or chuggle at light throttle cruise or coast

- Rough idle, cold or hot

CAUSE:

These conditions are related to EGR (Exhaust Gas Recirculation), fuel and spark control calibrations, and idle speed.

CORRECTION:





A new service calibration has been developed which contains updates to EGR, Fuel and Spark Control and increases idle speed to 700 rpm from 600 rpm. To correct any of the above conditions install a new prom (Programmable Read Only Memory) using the application chart.



NOTE:
1990 model year trucks require ECM (Engine Control Module) P/N 16144288 in order to use the new prom. 1991 model year trucks should already have this engine controller. Also note that the new calibration is nationwide, replacing both Federal and California emission original production calibrations.

SERVICE PARTS INFORMATION:
Parts are expected to be available on 10/12/92. In case of limited inventory, parts will be placed on 400 control to waive VIP surcharges. Only verifiable emergency VIP orders will be accepted. GMSPO will make every effort to obtain parts. However, the part will be shipped premium transportation at dealer's expense and all other order types will be placed on backorder until the 400 control is removed.

WARRANTY INFORMATION:

Labor Operation:
T0500

Labor Time:
0.8 Hr.