REVISED PROMS/DRIVEABILITY FALSE SERVICE ENGINE SOON. GMC Truck GMC Suburban

MODELS: 1987 AND EARLY 1988 R/V,C/K,AND G MODELS WITH 5.0L (VIN CODE H) AND 5.7L (VIN CODE K) ENGINES AND LIGHT DUTY EMISSIONS

THIS BULLETIN CANCELS AND SUPERSEDES TRUCK SERVICE BULLETIN 88-T-25 ALL COPIES OF WHICH SHOULD BE DESTROYED. THIS REVISION IS TO UPDATE PROM P/N'S AND ADD LABOR OP. AND TIME.

Some 1987 and early built 1988 R/V, C/K and G models with TBI engines may experience one or more of the following driveability conditions and/or false codes. If these conditions are experienced, they can be repaired by replacing the PROMs.

Driveability Conditions - 5.0L (L03) TBI Engine ------------------------ 1. Rolling, surging or rough idles. 2. False Code 54 - Fuel pump circuit (low voltage). 3. False Code 43 - ESC fault. 4. Tip-In Sags/Hesitations during engine warm-up.

Driveability Conditions - 5.7L (L05) TBI Engine ------------------------ 1. Rolling, surging or rough idles.

Notice: In addition to the PROM change it will be necessary to reset minimum idle speed, per the procedures on pg. 4-44 of the 1988 Driveability and Emissions Book X8836.

A. Automatic (Drive) 425 plus or minus 25 RPM.

B. Manual (Neutral) 500 plus or minus 25 RPM.

2. Low speed road load surge.

3. Detonation and weak acceleration during warm-up.

4. Poor cold starting at minus 20 degrees Fahrenheit.

5. False Code 24 - Vss circuit fault when using 4 wheel drive low lock.

6. Tip-In sags/hesitations during engine warm-up.

7. Long crank times, hot or cold.

Condition Service Action --------- --------------

Driveability On 1988 models, to determine whether or not the revised calibration PROM was built into the vehicle, use a "Scan" tool to check to see if vehicle has a revised calibration PROM (see chart atached). Install revised calibration PROM if vehicle is not so equipped.

Use Labor Op. J6364 Labor Time: .6 hr C,Y,R,V .7 hr G

L03 (5.0L) TBI ENGINE --------------------- NEW BROADCAST NEW PROM EMISSIONS NEW PROM CODE I.D. BODY SERIES TYPE TRANSMISSION AXLE KIT # (PROM (SCAN STYLE LABEL) TOOL) ------------------------------------------------------------------------------ Pickup 1500 Fed(NA5) 3 -Spd Auto. 2.73(GU2) 16120046 AMTS 9871 (M40) 3.08(GU4)

Pickup " " " " " " 3.42(GU6) 16120073 AMTT 9881 3.73(GU4)

Pickup " " " 4-Spd Auto. 2.73(GU2) 16120077 AMTU 9891 (MD8)

Pickup " " " " 3.08(GU4) 16120082 AMTW 9901

Pickup " " " " 3.42(GU6) 16120086 AMTX 9911 3.73(GT4)

Pickup " Altitude 3-Spd Auto. All 16120090 AMTY 9921 (NA6) (M40)

Pickup " " 4-Spd Auto. All 16120095 AMTZ 9931 (MD8)

Pickup 2500 Fed/Alt 3-Spd Auto. All 16120099 AMUA 0099 (NA5/NA6) (M40)

Pickup 15-2500 " " 4-Spd Auto. All 16120105 AMUB 9951 4WD (MD8)

Pickup 2500 " " " " All 16120105 " "

Suburban 1500 " " " " All 16120105 " "

Blazer/ 1500 " " " " All 16120105 " " Jimmy

L03 (5.0L) TBI ENGINE ---------------------

NEW BROADCAST NEW PROM BODY EMISSION NEW PROM CODE I.D. STYLE SERIES TYPE TRANSM. AXLE KIT # (PROM LABEL)(SCAN TOOL) ------------------------------------------------------------------------------

Pickup 12-2500 Fed/ALT 3-Spd Auto. All 16120109 AMUC 9961 4WD (NA5/NA6) (M40)

Pickup " " " " 5-Spd Man. All 16120114 AMUD 9971 (MG5)

Pickup " " " " " All 16120118 AMUF 9981 4WD

Pickup 1500 California 4-Spd Auto. 2.73 16120042 AMUH 9991 (NB2) (MD8) (GU2)

Pickup 1500 " 4-Spd Auto. 3.08 16120125 AMUJ 0001 (MD8) (GU4) 3.42(GU6) 3.73(GT4) AMUK 0011 Pickup 15-2500 " " " " " 4WD

Suburban 1500 " " " All 16120129 " "

Blazer/ 1500 " " " All 16120129 " " Jimmy

Sportvan/ 15-2500 " " " All 16120139 AMUL 0021 Rally

Sportvan/ 15-2500 Fed/Alt 4-Spd Auto. All 16120143 AMUM 0031 Rally (MD8)

Sportvan/ " " " " 3-Spd Man. All 16120147 AMUN 0041 Rally (M40)

Sportvan/ " " " " 4-Spd Man. All 16120151 AMUP 0051 Rally (MY6)

L05 (5.7L) TBI ENGINE ---------------------

NEW BROADCAST NEW PROM BODY EMISSIONS NEW PROM CODE I.D. STYLE SERIES TYPE TRANSM. AXLE KIT # (PROM LABEL) (SCAN TOOL) ------------------------------------------------------------------------------

Pickup 15-2500 Fed/Alt 4-Spd Auto. All 16120054 AMUR 0061 2&4 WD (NA5/NA6)

Suburban 1500 " " " " " All 16120054 " " 2&4 WD

Blazer/ " " " " " " All 16120054 " " Jimmy

Sportvan/ 15-25- " " " " " All 16120054 " " Rally 3500

Pickup 15-2500 California " " " All 16120059 AMUS 0071 2&4 WD (NB2)

Suburban 1500 " " " " All 16120059 " " 2&4 WD

Blazer/ " " " " " All 16120059 " " Jimmy

Sportvan/ 15-25- " " " " All 16120059 " " 3500

Pickup- 15-2500 Fed/Alt 4-Spd Man. All 16120064 AMUT 0081 2&4 WD (NA5/NA6) (M20)

Suburban- 1500 " " " All 16120064 " " 4 WD

Pickup 15-2500 " " 5-Spd Man. All 16120068 AMUU 0091 2&4 WD

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.