ROUGH IDLE/COLD START STALL (RPL. PROM/RESET MINIMUM IDLE)

SUBJECT: ROUGH IDLE COLD/COLD START STALL (REPLACE PROM AND RESET MINIMUM IDLE SPEED)

VEHICLES AFFECTED: 1991-93 "C6" "C7", "B7", "P6" TRUCKS WITH 6L GAS ENGINE.

CONDITION:

---------- Some owners of 1991, 1992, and early built 1993 model year C6, C7, B7, P6 trucks with the 6.OL gas engines may comment of rough idle cold or of a cold start stall.

CAUSE:

------ The cold spark curve in the calibration and idle speed were not optimal for all temperatures.

CORRECTION:

----------- In mid-March 1993, a new calibration and TBI unit entered production to help improve the above two conditions. If normal diagnostics cannot correct these conditions, replace PROM (see chart) and reset the minimum idle speed.

1. Connect Tech 1 scanner to data link connector and read PROM I.D. If I.D. is different than those listed in chart below, replace PROM.

Broadcast Scanner PROM Service Model Governor Code I.D. Part No. ----- -------- --------- -------- ------------ C6,C7,B7 VNC (45 mph) BDHA 6285 16186418 C6,C7,B7 VND (50 mph) BDHB 6295 16186423 C6,C7,B7 VNE (55 mph) BDHC 6305 16186426 C6,C7 LVA (60 mph) BDHD 6315 16186429 C6,C7 KYR (65 mph) BDHF 6225 16186433 C6,C7,B7,P6 (75 mph) BDFZ 6275 16186390

2. Set minimum idle speed to 575 (+/- 25) rpm per instructions in your 1993 model year Medium Duty Fuel and Emission Manual (see pages 4-15, 4-16).

Labour Labour Operation No. Operation Name Labour Time ------------ --------------- ----------- PROM Replace 0.8 Hours J5545 Minimum Speed Adjust 0.5 Hour

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.