WHITE/BLUE SMOKE ON COLD START DIAGNOSTIC PROCEDURE (PROM)

SUBJECT: WHITE OR BLUE SMOKE ON COLD START-UP (ADVANCE INJECTION PUMP TIMING AND NEW PROM)

VEHICLES AFFECTED: 1991 C/K/R/V AND G TRUCKS W/6.2 DIESEL

Condition:

----------- Following cold start-up, the engine misfires, runs rough and may produce objectionable blue or white smoke.

Cause:

--------- Some engines were timed too retarded and the housing pressure cold advance schedule controlled by the ECM was modified to a reduced time duration.

Correction:

------------- Engines timed with injection pump models DB-2829-4894 and 4895 below the injection pump serial number change point 6633950 and 6617332 respectively may be corrected by advancing (toward the driver side of the vehicle) the injection pump timing 1mm or 2 degrees crankshaft rotation. A new timing line should be stamped on the front cover to match the timing line on the injection pump flange. A letter 101 should then be stamped across the joint flange of both the engine timing cover and injection pump showing the correct timing by alignment of both halves of the letter 101. Correction of the housing pressure cold advance schedule will apply to all engines and requires replacement of the PROM's listed below:

6.2 DIESEL (RPO LH6) ------------------------

SCANNER BROADCAST PART MODEL EMISSION TRANS. I.D. CODE NUMBER ------- -------- ------------ -------- ---------- ---------- C/K FED (NA5) 4 SPEED 1415 AXMP 16161408 AUTO (MD8)

C/K ALT (NA6) 4 SPEED 1425 AXMR 16161410 MANUAL (M20) 5 SPEED MANUAL (MT8) R/V/G FED (NA5) ALL 1425 AXMR 16161410

R/V/G ALT (NA6) ALL 1435 AXMS 16161412

C/K FED (NA5) 4 SPEED 1445 AXMT 16161414 MANUAL (M20) 5 SPEED MANUAL (MT8)

Parts are currently available from CANSPO.

NOTE: Some early built 1991 models did not have the correct starting label. The correct starting procedure to minimize white smoke is as follows:

Procedure:

1. Turn ignition key to the "run" position, then depress the accelerator fully and release.

2. If glow plug/wait light is on, DO NOT crank the engine.

3. If glow plug/wait light does not come on, or when it goes off, turn ignition key to the "start" position and release the key when engine starts. If engine fails to start after 15 seconds cranking, return key to the "off" position. wait one minute for the starter to cool, then repeat procedure.

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.