LOW SPEED DRIVEABILTY (PROM) NEW KNOCK SENSOR AVAILABLE

SUBJECT: LOW SPEED DRIVEABILITY AND/OR CRECK ENGINE LIGHT CODE 43 (INSTALL KNOCK SENSOR AND MEMCAL OR PROM)

VEHICLES AFFECTED: 1990-91 'F' W/5.0L

THIS BULLETIN CANCELS AND SUPERSEDES PRODUCT SERVICE BULLETIN #90-650- 106 ALL COPIES SHOULD BE DISCARDED.

CONDITION:

----------- Some owners of 1990 and 1991 F-cars with the 5.OL Port Fuel Injection (VIN F, LB9) V8 engine may comment about low speed driveability or a Check Engine Light - Code 43 - Electronic Spark Control (ESC). Comments about LB9 driveability may include idle surge, unstable idle, or stall at stops.

Some owners of 1991 F-cars with the 5.OL Throttle Body Injection (VIN E, L03) V8 engine may also comment about a Check Engine Light - Code 43 (ESC).

CAUSE:

------ New calibrations have been released that refine idle speed control (LB9 only) and ESC diagnostics. A new knock sensor (LB9 Only) is also available which has improved durability characteristics.

CORRECTION:

------------ Install knock sensor (LB9 ONLY) P/N 10456126*, and install the applicable Memcal or PROM from the table below:

Service Scanner Broadcast Model Engine Application P/N I/D Code Year ---------- -------- --------- ------ ---------- ------------- **16163062 3061 AXXB 1991 LB9 Automatic with Chevrolet P235/55R16 Pontiac P215/60R16 or P215/65R15

**16163066 3071 AXXC 1991 LB9 Manual (M39) with Chevrolet P235/55R16 Pontiac P215/60R16 or P215/65R15

**16163075 3091 AXXF 1991 LB9 Automatic with P245/50ZR16

**16163070 3081 AXXD 1991 LB9 Manual with P245/50ZR16

**16163138 3271 AXYC 1990-91 LB9 Manual (MK6)

**16163137 3261 AXYB 1990 LB9 Manual (M39)

**16163139 3281 AXYD 1990 LB9 Automatic

* 16161112 1101 AXKT 1991 L03 Automatic with Federal Emissions

* 16161123 1121 AXKW 1991 L03 Manual (M39) with Federal Emissions

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.