Engine Controls - New PROM (Driveability/False Lights)
88chevy23GMC NUMBER: 88-T-109
GROUP: 6E - Engine Emission
DATE: May, 1988
CORPORATE
NUMBER: 836501R
SUBJECT: REVISED PROMS: TO ADDRESS DRIVEABILITY AND ELIMINATE FALSE "SERVICE ENGINE SOON" LIGHTS
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 RN, 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 warmup.
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 warmup.
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 attached). Install revised calibration PROM if vehicle is not so equipped.
Use Labor Op. J6364
Labor Time: .6 hr C,K,R,V .7 hr G