REVISED PROMS/DRIVEABILITY FALSE SERVICE ENGINE SOON. Chevrolet Chevy Suburban

Model and Year 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 (NA1)

TO: ALL CHEVROLET DEALERS

This bulletin cancels and replaced Dealer Service Bulletin 88-33 (Section 6E) dated July 1987, to release new PROMS with additional driveability improvements. All copies of 88-33 should be destroyed.

Some 1987-88 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. 4-22 OF THE DRIVEABILITY AND EMISSIONS BOOK.

A. Automatic (Drive) 425 plus or minus 25 RPM B. Manual (Neutral) 500 plus or minimum 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/Hesitation during engine warm-up. 7. Long crank times, hot or cold.

To repair the above conditions install PROMs per the following chart.

Use applicable Labor time and Operation number.

L03 (5.0L) TBI ENGINE --------------------- EMISSIONS NEW PROM BODY STYLE SERIES TYPE TRANSMISSION AXLE KIT ---------- ------ ---- ----------- ------ ---

Pickup 4WD 15-2500 Fed/Alt 3-Spd Auto.(M40) All 16120109 (NA5/NA6) Pickup " " 5-Spd Man.(MG5) All 16120114 Pickup 4WD " " " " " " All 16120118 Pickup 1500 California 4-Spd Auto.(MD8) 2.73(GU2) 16120042 (NB2) Pickup 1500 " 4-Spd Auto.(MD8) 3.08(GU4) 16120125 3.42(GU6) 3.73(GT4)

Pickup 4WD 15-2500 " " " " 16120129 Suburban 10 " " " " All 16120129

Blazer 10 " " " " All 16120129 " " " Sportvan 10-20 " All 16120139 Sportvan " Fed/Alt 4-Spd Auto.(MD8) All 16120143 (NA5/NA6)

Sportvan " " 3-Spd Auto.(M40) All 16120147 Sportvan " " 4-Spd Man.(MY6) All 16120151

NEW BROADCAST NEW PROM CPDE I.D. BODY STYLE (PROM LABEL) (SCAN TOOL) ---------- ---------- --------- Pickup 4WD AMUC 9961

Pickup AMUD 9971 Pickup 4WD AMUF 9981 Pickup AMUH 9991

Pickup AMUJ 0001

Pickup 4WD AMUK 0011 Suburban " "

Blazer " "

Sportvan AMUL 0021 Sportvan AMUM 0031

Sportvan AMUN 0041 Sportvan AMUP 0051

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

EMISSIONS NEW PROM BODY STYLE SERIES TYPE TRANSMISSION AXLE KIT ---------- ------ ---- ------------- ---- ----

Pickup-2&4WD 15-2500 Fed/Alt 4-Spd Auto.(MD8) All 16120054 (NA5/NA6) Suburban-2&4WD 10 " " All 16120054

Blazer " " " All 16120054

Sportvan 10-20-30 " " All 16120054

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

Suburban-2&4WD 10 " " All 16120059

Blazer " " " All 16120059

Sportvan 10-20-30 " " All 16120059

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

Suburban-4WD 10 " " All 16120064

Pickup-2&4WD 15-2500 " 5-Spd Man.(MG5) All 16120068

NEW BROADCAST NEW PROM CODE I.D. BODY STYLE (PROM LABEL) (SCAN TOOL) ----------- ------------ -----------

Pickup-2&4WD AMUR 0061

Suburban-2&4WD " "

Blazer " "

Sportvan " "

Pickup-2&4 WD AMUS 0071 "

Suburban-2&4WD " "

Blazer " "

Sportvan " "

Pickup-2&4WD AMUT 0081 "

Suburban-4WD " "

Pickup-2&4WD AMUU 0091

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

EMISSIONS NEW PROM BODY STYLE SERIES TYPE TRANSMISSION AXLE KIT # ---------- ------ ---- ------------ ---- -------

Pickup 1500 Fed (NA5) 3-Spd Auto.(M40) 2.73(GU2) 16120046 3.08(GU4)

Pickup " " " 3.42(GU6) 16120073 3.73(GU4) " Pickup " 4-Spd Auto.(MD8) 2.73(GU2) 16120077

Pickup " " " 3.08(GU4) 16120082

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

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

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

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

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

Pickup 2500 " " All 16120105

Suburban 10 " " All 16120105

Blazer 10 " " All 16120105

NEW BROADCAST NEW PROM CODE I.D. BODY STYLE (PROM LABEL) (SCAN TOOL) ---------- ------------ -----------

Pickup AMTS 9871

Pickup AMTT 9881

Pickup AMTU 9891

Pickup AMTW 9901

Pickup AMTX 9911

Pickup AMTY 9921

Pickup AMTZ 9931

Pickup AMUA 0099

Pickup 4WD AMUB 9951

Pickup " "

Suburban " "

Blazer " "

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.