Rear Wheels - Unable to Stop Turning on Icy Surfaces
87chevy05CHEVROLET NUMBER: 86-T-218
SECTION: 5 - Brakes
DATE: February, 1987
SUBJECT: REAR WHEELS TURN ON ICE
MODELS: 1985-86 SAFARI/ASTRO VANS WITH 4.3L ENGINE AND AUTOMATIC TRANSMISSION
Some customers may experience a condition immediately after cold vehicle startup where, by applying the brake pedal, they are unable to completely stop the rear wheels from turning on icy surfaces. Variables such as rear axle ratios and higher engine rpm while the vehicle is in the cold idle mode can result in increased torque to the rear wheels. These variables, in conjunction with a lightly loaded rear axle, can increase the pedal effort required to stop the rear wheels from spinning on ice when the vehicle is placed in gear. This condition can be effectively addressed by using the following procedure to reduce the cold idle speed of the engine.
NOTE: Separate procedures to reduce engine cold idle speed apply to each model year.
FIGURE NO. 1 - TACHOMETER TERMINAL AT DISTRIBUTOR CAP:
1985 MODEL 4.3L CARBURETED ENGINE
Reduce cold idle speed to 1600 rpm.
1. Remove dash extension.
2. Remove engine cover.
3. Install tachometer. The tachometer (tach) terminal is next to the engine control switch (bat) connector on the distributor cap (Reference Figure No. 1).
NOTE: The tachometer terminal must never be allowed to touch ground, because damage to the module inside the distributor and/or ignition coil can result
4. Reduce cold idle speed to 1600 rpm by adjusting the fast idle screw. Refer to time up label for procedure.
5. Remove tachometer and reinstall engine cover and dash extension.
6. On a dean dry surface, next to the existing tune up label located on the fan shroud, place label P/N 10066488.
FIGURE NO. 2 - ECM - ASSEMBLY:
1986 MODEL 4.3L TBI ENGINES
The cold engine idle speed of the 1986 models is to be reduced by the replacement of the PROM, reference Figure No. 2. 1986 model vehicles built before VINS listed below require PROM replacement
GMC GB524481 Federal Emissions
GB524599 California Emissions
Chevrolet GB203188 Federal Emissions
GB203623 California Emissions
Vehicles built after these VIN breakpoints have the recalibrated PROM factory installed.
NOTE: Any time the PROM is installed backwards and the ignition switch turned on, the PROM is destroyed and must be replaced.
1. Disconnect negative battery cable.
2. Remove kick panel from right side of the vehicle (1 screw) interior.
3. Remove ECM (2 screws).
4. Disconnect electrical harnesses from ECM module.
5. Remove ECM cover (2 screws).
6. Remove PROM from ECM and replace with new PROM, P/N 16068877 (Federal), P/N 16068926 (California).
7. Replace ECM cover.
8. Reconnect electrical harness.
9. Secure ECM module to its mounting location.
10. Replace kick panel.
PARTS LIST
Label (1985 Model Only) P/N 10066488
PROM Federal/High Altitude P/N 16068877
Emissions
PROM California Emissions P/N 16068926