COLD ENGINE KNOCK - INSTALL CHECK VALVE OIL FILTER/CHANGE
SUBJECT: COLD ENGINE KNOCK (INSTALL CHECK VALVE OIL FILTER/REPLACE PROM)
MODELS: 1991-93 C/K, R/V, WL, S/T, G TRUCKS (VINS K, N, Z)
CONDITION:
--------- Some late model LB4 (VIN Z, 4.3L, V6), L05 (VIN K, 5.7L, VB), and L19 (VIN N, 7.4L, V8) truck engines have been reported to exhibit "cold knock" on start up. "Cold knock" usually occurs after the vehicle has been completely warmed, then parked for 8 or more hours in ambient temperatures of 35 degrees Fahrenheit or less. "Cold knock" can be separated into three distinct categories.
A. Short Duration - Harsh deep metallic knock that usually lasts from 1 to 10 seconds. Generally classified as a bearing or rod knock.
B. Valve Train - Light clatter, tick or click that may last up to 1 minute.
C. Piston Slap - Metallic knock that occurs only under load. Piston slap may last as long as 5 minutes.
CORRECTION - CATEGORY A: Short Duration Knock
For 1992 LB4, 4.3L, VIN Z ONLY:
Install PF52 oil filter. Install a revised PROM that reduces the engine spark advance after the engine is started. The reduction in spark lowers the cylinder pressure and eliminates the knock. The revised PROM will NOT eliminate a piston slap (Category C) or valve train noise (Category B) concern. The base cold knock PROMs contain the previously released calibration update for torque converter clutch (TCC) lock-up (see Corporate Bulletin 137107) if the vehicle has an automatic transmission, or neutral gear rattle if the vehicle has a manual transmission (see Corporate Bulletin 267201 R). If a vehicle has had a detonation fix PROM installed previously, select the combined detonation and cold knock fix PROM for the application. See Corporate Bulletin 376508 for more information on detonation.
NOTE: Use of a detonation fix PROM in a non-detonating vehicle may result in degraded driveability. SPO will be temporarily stocking four (4) PROMs for each light duty 1992 model year LB4 application.
Base Detonation Fix Cold Knock Fix Combination Cold Knock and Detonation Fix
The detonation fix (detonation fix only) PROMs will not be restocked by SPO when the current supply is exhausted. If a detonation fix PROM is required after the existing stock is exhausted, the combination cold knock and detonation PROM is to be used. Special Parts Assistance Center will have information available on each PROM. Select the PROM from the table below. Old broadcast code (OLD B/C Code) information has been supplied to help determine if a detonation fix PROM has been installed previously. If the Old B/C Code can be found in the first table, a detonation fix has not been installed. If the broadcast code cannot be found in the tables below, call the appropriate marketing division technical assistance group. PROMs are expected to be available from GMSPO August 30, 1993.
1992 LB4, VIN Z
For Vehicles With "Cold Knock" Only
Old Trans Axle Service PROM B/C Scan B/C Platform RPO RPO Emission Class Kit Code I.D. Code ----------------------------------------------------------------------------- C1,2/K1,2 MD8 ALL NA5/NA6 16198453 BJMN 8455 AULF C1,2/K1,2 MD8 ALL NB2 16198460 BJMR 8475 AULK C1,2 MG5 ALL NA5/NA6 16198529 BJNR 8675 BDCW or AULH C1,2 MG5 ALL NB2 16198542 BJNW 8715 BDCX or AULL C1,2/K1,2 MT8 ALL NA5/NA6+NA1 16198536 BJNT 8695 BCZP or AULJ K1,2 MG5 ALL NA5/NA6+NA1 16198536 BJNT 8695 BCZP or AZUS C1,2/K1,2 MT8 ALL NB2+NA1 16198549 BJNY 8735 BCZR or AULM K1,2 MG5 ALL NB2+NA1 16198549 BJNY 8735 BCZR or AZUT S/T MD8 ALL NA5/NA6 16198467 BJMT 8495 BARL or AWHH S/T MD8 ALL NB2 16198473 BJMW 8515 BARM or AWHF S/T MY2 GU2 NA5/NA6/NB2 16198507 BJNJ 8615 BHSF or AULR S/T MY2 GU4 NA5/NA6/NB2 16198513 BJNL 8635 BHSH or AULS S/T MY2 GU6 NA5/NA6/NB2 16198522 BJNN 8655 BHSJ or AULT G1,2,3/M1 MD8 ALL NA5/NA6 16198480 BJMY 8535 AULN G1,2,3/M1 MD8 ALL NB2 16198493 BJNC 8575 AULP L MD8 ALL NA5/NA6 16198487 BJNA 8555 AYAW or BCNU L MD8 ALL NB2 16198500 BJNF 8595 AYAX or BCNW
For Vehicle: with "Cold Knock" Having Previously Installed Detonation Field Fix PROM
-OR-
For Vehicles with "Cold Knock" and Detonation
Trans Axle Service PROM B/C Scan Old B/C Platform RPO RPO Emission Class Kit Code I.D. Code ----------------------------------------------------------------------------- C1,2/K1,2 MD8 ALL NA5/NA6 16198457 BJMP 8465 BFNC C1,2/K1,2 MD8 ALL NB2 16198463 BJMS 8485 BFND C1,2 MG5 ALL NA5/NA6 16198532 BJNS 8685 BHSM C1,2 MG5 ALL NB2 16198546 BJNX 8725 BHUT C1,2/K1,2 MT8 ALL NA5/NA6+NA1 16198539 BJNU 8705 BHSN K1,2 MG5 ALL NA5/NA6+NA1 16198536 BJNU 8705 BHSN C1,2/K1,2 MT8 ALL NB2+NA1 16198552 BJNZ 8745 BFND K1,2 MG5 ALL NB2+NA1 16198552 BJNZ 8745 BFND S/T MD8 ALL NA5/NA6 16198470 BJMU 8505 BFNF S/T MD8 ALL NB2 16198477 BJMX 8525 BFNH S/T MY2 GU2 NA5/NA6/NB2 16198510 BJNK 8625 BHWN S/T MY2 GU4 NA5/NA6/NB2 16198518 BJNM 8645 BHWP S/T MY2 GU6 NA5/NA6/NB2 16198526 BJNP 8665 BHWR G1,2,3/M1 MD8 ALL NA5/NA6 16198483 BJMZ 8545 BHSA G1,2,3/M1 MD8 ALL NB2 16198497 BJND 8585 BHSC L MDB ALL NA5/NA6 16198490 BJNB 8565 BHSB L MD8 ALL L NB2 16198503 BJNH 8605 BHSD
For 1991-93 model year L05 and L19, 1991 and 1993 LB4 engines, two actions have been found to show a high probability of success in curing short duration cold knock (Category A). General Motors suggests performing the following steps.
NOTE: These steps are only applicable to short duration cold knock, and will not eliminate a knock occurring under load. Neither will these actions eliminate a knock lasting more than 10 seconds nor a knock occurring in a hot or warm engine.
Step 1: Install a check valve oil filter
Original Filter Install
PF35 AC PF1218
PF51 AC PF52
Step 2: Change the oil; use a synthetic oil meeting the API Service SG or SG/CE standard.
NOTE: This action is only required once; conventional (non- synthetic) API Service SG or SG/CE oil may be reinstalled at the next oil change.
If an LB4 (VIN Z, 4.3L, V6) or an L05 (VIN K, 5.7L, V8) continues to exhibit short duration cold knock after performing steps one and two and accumulating- at least 200 miles, call the appropriate marketing division technical assistance group.
CORRECTION - CATEGORY B: Valve Train Chatter, Tick, or Click. ------------------------------------------------------------- For 1992 or 1993 vehicles equipped with a Romulus built (adjustable lash) LB4 (VIN Z, 4.3L, V6) engine, adjust valve lash. Bulletin 376107 provides information on this procedure and on how to identify Romulus-produced engines.
Investigation of "cold knock" is continuing. Updates will continue to be provided when available. Parts are expected to be available from GMSPO August 30, 1993.
WARRANTY INFORMATION
For vehicles repaired under warranty, use:
Labor Op Description Labor Time ----- ----------- ---------- J0950 Filter and Oil See Applicable Replace Labor Time Guide For 1992 LB4 vehicles, use:
Labor Op Description Labor Time -------- ----------- ---------- T0500 PROM Replace 1 0.5 hours
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.
